2021 Vol. 12, No. 3
2021, 12(3): 101079.
doi: 10.1016/j.gsf.2020.08.015
Abstract:
More than 2.5 billion people on the globe rely on groundwater for drinking and providing high-quality drinking water has become one of the major challenges of human society. Although groundwater is considered as safe, high concentrations of heavy metals like arsenic (As) can pose potential human health concerns and hazards. In this paper, we present an overview of the current scenario of arsenic contamination of groundwater in various countries across the globe with an emphasis on the Indian Peninsula. With several newly affected regions reported during the last decade, a significant increase has been observed in the global scenario of arsenic contamination. It is estimated that nearly 108 countries are affected by arsenic contamination in groundwater (with concentration beyond maximum permissible limit of 10 ppb recommended by the World Health Organization. The highest among these are from Asia (32) and Europe (31), followed by regions like Africa (20), North America (11), South America (9) and Australia (4). More than 230 million people worldwide, which include 180 million from Asia, are at risk of arsenic poisoning. Southeast Asian countries, Bangladesh, India, Pakistan, China, Nepal, Vietnam, Burma, Thailand and Cambodia, are the most affected. In India, 20 states and 4 Union Territories have so far been affected by arsenic contamination in groundwater. An attempt to evaluate the correlation between arsenic poisoning and aquifer type shows that the groundwater extracted from unconsolidated sedimentary aquifers, particularly those which are located within the younger orogenic belts of the world, are the worst affected. More than 90% of arsenic pollution is inferred to be geogenic. We infer that alluvial sediments are the major source for arsenic contamination in groundwater and we postulate a strong relation with plate tectonic processes, mountain building, erosion and sedimentation. Prolonged consumption of arsenic-contaminated groundwater results in severe health issues like skin, lung, kidney and bladder cancer; coronary heart disease; bronchiectasis; hyperkeratosis and arsenicosis. Since the major source of arsenic in groundwater is of geogenic origin, the extend of pollution is complexly linked with aquifer geometry and aquifer properties of a region. Therefore, remedial measures are to be designed based on the source mineral, climatological and hydrogeological scenario of the affected region. The corrective measures available include removing arsenic from groundwater using filters, exploring deeper or alternative aquifers, treatment of the aquifer itself, dilution method by artificial recharge to groundwater, conjunctive use, and installation of nano-filter, among other procedures. The vast majority of people affected by arsenic contamination in the Asian countries are the poor who live in rural areas and are not aware of the arsenic poisoning and treatment protocols. Therefore, creating awareness and providing proper medical care to these people remain as a great challenge. Very few policy actions have been taken at international level over the past decade to reduce arsenic contamination in drinking water, with the goal of preventing toxic impacts on human health. We recommend that that United Nations Environment Programme (UNEP) and WHO should take stock of the global arsenic poisoning situation and launch a global drive to create awareness among people/medical professionals/health workers/administrators on this global concern.
More than 2.5 billion people on the globe rely on groundwater for drinking and providing high-quality drinking water has become one of the major challenges of human society. Although groundwater is considered as safe, high concentrations of heavy metals like arsenic (As) can pose potential human health concerns and hazards. In this paper, we present an overview of the current scenario of arsenic contamination of groundwater in various countries across the globe with an emphasis on the Indian Peninsula. With several newly affected regions reported during the last decade, a significant increase has been observed in the global scenario of arsenic contamination. It is estimated that nearly 108 countries are affected by arsenic contamination in groundwater (with concentration beyond maximum permissible limit of 10 ppb recommended by the World Health Organization. The highest among these are from Asia (32) and Europe (31), followed by regions like Africa (20), North America (11), South America (9) and Australia (4). More than 230 million people worldwide, which include 180 million from Asia, are at risk of arsenic poisoning. Southeast Asian countries, Bangladesh, India, Pakistan, China, Nepal, Vietnam, Burma, Thailand and Cambodia, are the most affected. In India, 20 states and 4 Union Territories have so far been affected by arsenic contamination in groundwater. An attempt to evaluate the correlation between arsenic poisoning and aquifer type shows that the groundwater extracted from unconsolidated sedimentary aquifers, particularly those which are located within the younger orogenic belts of the world, are the worst affected. More than 90% of arsenic pollution is inferred to be geogenic. We infer that alluvial sediments are the major source for arsenic contamination in groundwater and we postulate a strong relation with plate tectonic processes, mountain building, erosion and sedimentation. Prolonged consumption of arsenic-contaminated groundwater results in severe health issues like skin, lung, kidney and bladder cancer; coronary heart disease; bronchiectasis; hyperkeratosis and arsenicosis. Since the major source of arsenic in groundwater is of geogenic origin, the extend of pollution is complexly linked with aquifer geometry and aquifer properties of a region. Therefore, remedial measures are to be designed based on the source mineral, climatological and hydrogeological scenario of the affected region. The corrective measures available include removing arsenic from groundwater using filters, exploring deeper or alternative aquifers, treatment of the aquifer itself, dilution method by artificial recharge to groundwater, conjunctive use, and installation of nano-filter, among other procedures. The vast majority of people affected by arsenic contamination in the Asian countries are the poor who live in rural areas and are not aware of the arsenic poisoning and treatment protocols. Therefore, creating awareness and providing proper medical care to these people remain as a great challenge. Very few policy actions have been taken at international level over the past decade to reduce arsenic contamination in drinking water, with the goal of preventing toxic impacts on human health. We recommend that that United Nations Environment Programme (UNEP) and WHO should take stock of the global arsenic poisoning situation and launch a global drive to create awareness among people/medical professionals/health workers/administrators on this global concern.
2021, 12(3): 101096.
doi: 10.1016/j.gsf.2020.10.003
Abstract:
The Naga Hills Ophiolite (NHO) belt in the Indo-Myanmar range (IMR) represents a segment of Tethyan oceanic crust and upper mantle that was involved in an eastward convergence and collision of the Indian Plate with the Burmese Plate during the Late Cretaceous-Eocene. Here, we present a detailed petrological and geochemical account for the mantle and crustal sections of NHO, northeastern India to address (i) the mantle processes and tectonic regimes involved in their genesis and (ii) their coherence in terms of the thermo-tectonic evolution of Tethyan oceanic crust and upper mantle. The NHO suite comprises well preserved crustal and mantle sections discretely exposed at Moki, Ziphu, Molen, Washelo and Lacham areas. The ultramafic-mafic lithologies of NHO are mineralogically composed of variable proportions of olivine, orthopyroxene, clinopyroxene and plagioclase. The primary igneous textures for the mantle peridotites have been overprinted by extensive serpentinisation whereas the crustal section rocks reflect crystal cumulation in a magma chamber. Chondrite normalised REE profiles for the cumulate peridotite-olivine gabbro-gabbro assemblage constituting the crustal section of NHO show flat to depleted LREE patterns consistent with their generation from depleted MORB-type precursor melt in an extensional tectonic setting, while the mantle peridotites depict U-shaped REE patterns marked by relative enrichment of LREE and HREE over MREE. These features collectively imply a dual role of depleted MORB-type and enriched arc-type mantle components for their genesis with imprints of melt-rock and fluid-rock interactions. Tectonically, studied lithologies from NHO correspond to a boninitic to slab-proximal Island Arc Tholeiite affinity thereby conforming to an intraoceanic supra subduction zone (SSZ) fore-arc regime coherent with the subduction initiation process. The geochemical attributes for the crustal and mantle sections of NHO as mirrored by Zr/Hf, Zr/Sm, Nb/Ta, Zr/Nb, Nb/U, Ba/Nb, Ba/Th, Ba/La and Nd/Hf ratios propound a two-stage petrogenetic process:(i) a depleted fore arc basalt (FAB) type tholeiitic melt parental to the crustal lithologies was extracted from the upwelling asthenospheric mantle at SSZ fore-arc extensional regime thereby rendering a refractory residual upper mantle; (ii) the crust and upper mantle of the SSZ fore arc were progressively refertilised by boninitic melts generated in response to subduction initiation and slab-dehydration. The vestiges of Tethyan oceanic lithosphere preserved in NHO represent an accreted intra-oceanic fore arc crust and upper mantle section which records a transitional geodynamic evolution in a SSZ regime marked by subduction initiation, fore arc extension and arc-continent accretion.
The Naga Hills Ophiolite (NHO) belt in the Indo-Myanmar range (IMR) represents a segment of Tethyan oceanic crust and upper mantle that was involved in an eastward convergence and collision of the Indian Plate with the Burmese Plate during the Late Cretaceous-Eocene. Here, we present a detailed petrological and geochemical account for the mantle and crustal sections of NHO, northeastern India to address (i) the mantle processes and tectonic regimes involved in their genesis and (ii) their coherence in terms of the thermo-tectonic evolution of Tethyan oceanic crust and upper mantle. The NHO suite comprises well preserved crustal and mantle sections discretely exposed at Moki, Ziphu, Molen, Washelo and Lacham areas. The ultramafic-mafic lithologies of NHO are mineralogically composed of variable proportions of olivine, orthopyroxene, clinopyroxene and plagioclase. The primary igneous textures for the mantle peridotites have been overprinted by extensive serpentinisation whereas the crustal section rocks reflect crystal cumulation in a magma chamber. Chondrite normalised REE profiles for the cumulate peridotite-olivine gabbro-gabbro assemblage constituting the crustal section of NHO show flat to depleted LREE patterns consistent with their generation from depleted MORB-type precursor melt in an extensional tectonic setting, while the mantle peridotites depict U-shaped REE patterns marked by relative enrichment of LREE and HREE over MREE. These features collectively imply a dual role of depleted MORB-type and enriched arc-type mantle components for their genesis with imprints of melt-rock and fluid-rock interactions. Tectonically, studied lithologies from NHO correspond to a boninitic to slab-proximal Island Arc Tholeiite affinity thereby conforming to an intraoceanic supra subduction zone (SSZ) fore-arc regime coherent with the subduction initiation process. The geochemical attributes for the crustal and mantle sections of NHO as mirrored by Zr/Hf, Zr/Sm, Nb/Ta, Zr/Nb, Nb/U, Ba/Nb, Ba/Th, Ba/La and Nd/Hf ratios propound a two-stage petrogenetic process:(i) a depleted fore arc basalt (FAB) type tholeiitic melt parental to the crustal lithologies was extracted from the upwelling asthenospheric mantle at SSZ fore-arc extensional regime thereby rendering a refractory residual upper mantle; (ii) the crust and upper mantle of the SSZ fore arc were progressively refertilised by boninitic melts generated in response to subduction initiation and slab-dehydration. The vestiges of Tethyan oceanic lithosphere preserved in NHO represent an accreted intra-oceanic fore arc crust and upper mantle section which records a transitional geodynamic evolution in a SSZ regime marked by subduction initiation, fore arc extension and arc-continent accretion.
2021, 12(3): 101098.
doi: 10.1016/j.gsf.2020.10.005
Abstract:
Whilst traditional approaches to geochemistry provide valuable insights into magmatic processes such as melting and element fractionation, by considering entire regional data sets on an objective basis using machine learning algorithms (MLAs), we can highlight new facets within the broader data structure and significantly enhance previous geochemical interpretations. The platinum-group element (PGE) budget of lavas in the North Atlantic Igneous Province (NAIP) has been shown to vary systematically according to age, geographic location and geodynamic environment. Given the large multi-element geochemical data set available for the region, MLAs were employed to explore the magmatic controls on these shifting concentrations. The key advantage of using machine learning in analysis is its ability to cluster samples across multi-dimensional (i.e., multi-element) space. The NAIP data set is manipulated using Principal Component Analysis (PCA) and t-Distributed Stochastic Neighbour Embedding (t-SNE) techniques to increase separability in the data alongside clustering using the k-means MLA. The new multi-element classification is compared to the original geographic classification to assess the performance of both approaches. The workflow provides a means for creating an objective high-dimensional investigation on a geochemical data set and particularly enhances the identification of metallogenic anomalies across the region. The techniques used highlight three distinct multi-element end-members which successfully capture the variability of the majority of elements included as input variables. These end-members are seen to fluctuate in prominence throughout the NAIP, which we propose reflects the changing geodynamic environment and melting source. Crucially, the variability of Pt and Pd are not reflected in MLA-based clustering trends, suggesting that they vary independently through controls not readily demonstrated by the NAIP major or trace element data structure (i.e., other proxies for magmatic differentiation). This data science approach thus highlights that PGE (here signalled by Pt/Pd ratio) may be used to identify otherwise localised or cryptic geochemical inputs from the subcontinental lithospheric mantle (SCLM) during the ascent of plume-derived magma, and thereby impact upon the resulting metallogenic basket.
Whilst traditional approaches to geochemistry provide valuable insights into magmatic processes such as melting and element fractionation, by considering entire regional data sets on an objective basis using machine learning algorithms (MLAs), we can highlight new facets within the broader data structure and significantly enhance previous geochemical interpretations. The platinum-group element (PGE) budget of lavas in the North Atlantic Igneous Province (NAIP) has been shown to vary systematically according to age, geographic location and geodynamic environment. Given the large multi-element geochemical data set available for the region, MLAs were employed to explore the magmatic controls on these shifting concentrations. The key advantage of using machine learning in analysis is its ability to cluster samples across multi-dimensional (i.e., multi-element) space. The NAIP data set is manipulated using Principal Component Analysis (PCA) and t-Distributed Stochastic Neighbour Embedding (t-SNE) techniques to increase separability in the data alongside clustering using the k-means MLA. The new multi-element classification is compared to the original geographic classification to assess the performance of both approaches. The workflow provides a means for creating an objective high-dimensional investigation on a geochemical data set and particularly enhances the identification of metallogenic anomalies across the region. The techniques used highlight three distinct multi-element end-members which successfully capture the variability of the majority of elements included as input variables. These end-members are seen to fluctuate in prominence throughout the NAIP, which we propose reflects the changing geodynamic environment and melting source. Crucially, the variability of Pt and Pd are not reflected in MLA-based clustering trends, suggesting that they vary independently through controls not readily demonstrated by the NAIP major or trace element data structure (i.e., other proxies for magmatic differentiation). This data science approach thus highlights that PGE (here signalled by Pt/Pd ratio) may be used to identify otherwise localised or cryptic geochemical inputs from the subcontinental lithospheric mantle (SCLM) during the ascent of plume-derived magma, and thereby impact upon the resulting metallogenic basket.
2021, 12(3): 101075.
doi: 10.1016/j.gsf.2020.09.006
Abstract:
Floods are one of nature's most destructive disasters because of the immense damage to land, buildings, and human fatalities. It is difficult to forecast the areas that are vulnerable to flash flooding due to the dynamic and complex nature of the flash floods. Therefore, earlier identification of flash flood susceptible sites can be performed using advanced machine learning models for managing flood disasters. In this study, we applied and assessed two new hybrid ensemble models, namely Dagging and Random Subspace (RS) coupled with Artificial Neural Network (ANN), Random Forest (RF), and Support Vector Machine (SVM) which are the other three state-of-the-art machine learning models for modelling flood susceptibility maps at the Teesta River basin, the northern region of Bangladesh. The application of these models includes twelve flood influencing factors with 413 current and former flooding points, which were transferred in a GIS environment. The information gain ratio, the multicollinearity diagnostics tests were employed to determine the association between the occurrences and flood influential factors. For the validation and the comparison of these models, for the ability to predict the statistical appraisal measures such as Freidman, Wilcoxon signed-rank, and t-paired tests and Receiver Operating Characteristic Curve (ROC) were employed. The value of the Area Under the Curve (AUC) of ROC was above 0.80 for all models. For flood susceptibility modelling, the Dagging model performs superior, followed by RF, the ANN, the SVM, and the RS, then the several benchmark models. The approach and solution-oriented outcomes outlined in this paper will assist state and local authorities as well as policy makers in reducing flood-related threats and will also assist in the implementation of effective mitigation strategies to mitigate future damage.
Floods are one of nature's most destructive disasters because of the immense damage to land, buildings, and human fatalities. It is difficult to forecast the areas that are vulnerable to flash flooding due to the dynamic and complex nature of the flash floods. Therefore, earlier identification of flash flood susceptible sites can be performed using advanced machine learning models for managing flood disasters. In this study, we applied and assessed two new hybrid ensemble models, namely Dagging and Random Subspace (RS) coupled with Artificial Neural Network (ANN), Random Forest (RF), and Support Vector Machine (SVM) which are the other three state-of-the-art machine learning models for modelling flood susceptibility maps at the Teesta River basin, the northern region of Bangladesh. The application of these models includes twelve flood influencing factors with 413 current and former flooding points, which were transferred in a GIS environment. The information gain ratio, the multicollinearity diagnostics tests were employed to determine the association between the occurrences and flood influential factors. For the validation and the comparison of these models, for the ability to predict the statistical appraisal measures such as Freidman, Wilcoxon signed-rank, and t-paired tests and Receiver Operating Characteristic Curve (ROC) were employed. The value of the Area Under the Curve (AUC) of ROC was above 0.80 for all models. For flood susceptibility modelling, the Dagging model performs superior, followed by RF, the ANN, the SVM, and the RS, then the several benchmark models. The approach and solution-oriented outcomes outlined in this paper will assist state and local authorities as well as policy makers in reducing flood-related threats and will also assist in the implementation of effective mitigation strategies to mitigate future damage.
2021, 12(3): 101097.
doi: 10.1016/j.gsf.2020.10.004
Abstract:
In continental subduction complexes minor volumes of high-pressure mafic rocks (eclogites) often co-exist with much more abundant felsic (granitic) and metasedimentary rocks, which are vital for resolving the origin and metamorphic evolution of subducted continental crust. In SW Mongolia, the Alag Khadny eclogite-bearing accretionary complex (AKC) is assumed to represent either a remnant of oceanic slab, or a continental margin, subducted in the Early Cambrian. Here we present geochronological, geochemical and petrological evidence of subduction records for the three major types of lithologies that host mafic eclogites, including Mesoproterozoic and Neoproterozoic granitic basement and overlying Neoproterozoic continental-margin sediments. Variably deformed, ferroan and peraluminous metagranitoids compose a major part of AKC and are interlayered with eclogites in its southern and eastern margins. They have geochemical features of post-collisional/intraplate high-K calc-alkaline granites. LA-ICP-MS U-Pb zircon geochronology of three distinct metagranite samples show uniform protolith crystallization ages of ca. 0.96 Ga and uncertain re-crystallization in the Late Neoproterozoic or Early Paleozoic metamorphic event, whereas abundant zircon inheritance indicates older, Mesoproterozoic to Paleoproterozoic crustal substrate during granite generation. The existence of Mesoproterozoic crust is highlighted by finding of distinct metagranitoids with the U-Pb zircon crystallization age of ca. 1.6 Ga. Hafnium isotope signatures (TDMC 2.88-1.85 Ga) of zircons from all lithologies preserved the evidence of reworked Neoarchean to Paleoproterozoic crust, similar to that of the Baidrag block (southern Mongolia), for both Mesoproterozoic and Neoproterozoic rocks. Regardless of the specific lithology, the rocks display indicators of high-pressure metamorphic re-equilibration, including garnet (XCa up to 0.65) + epidote + phengite (Si p.f.u. up to 3.56) ± rutile assemblage in metagranitoids, garnet + phengite (Si p.f.u. up to 3.42) in quartz-rich semi-pelites and garnet + phengite (Si p.f.u. up to 3.39) + medium-Mg chloritoid (XMg up to 0.25) + kyanite + rutile in metapelites. Corresponding P-T conditions recovered from different lithologies reveal incoherent subduction of rocks, which could be shallow for granitic basement (1.1-1.4 GPa and 600-670℃) and clastic metasediments (1.4-1.6 GPa, 570-620℃), but deeper for metapelites (2.1-2.3 GPa, 500-570℃). consistent with that of eclogites, The combined data show that the Alag Khadny complex represents a remnant of a rifted Mesoproterozoic to Neoproterozoic (ca. 1.6-0.96 Ga) continental margin consequently metamorphosed under HP conditions during Late Neoproterozoic-Early Cambrian evolution of the southern Central Asian Orogenic Belt. Acquired P-T estimates imply that high-pressure metagranitoids and metasedimentary rocks equilibrated at different depths, but most likely shared a common subduction-related metamorphic evolution.
In continental subduction complexes minor volumes of high-pressure mafic rocks (eclogites) often co-exist with much more abundant felsic (granitic) and metasedimentary rocks, which are vital for resolving the origin and metamorphic evolution of subducted continental crust. In SW Mongolia, the Alag Khadny eclogite-bearing accretionary complex (AKC) is assumed to represent either a remnant of oceanic slab, or a continental margin, subducted in the Early Cambrian. Here we present geochronological, geochemical and petrological evidence of subduction records for the three major types of lithologies that host mafic eclogites, including Mesoproterozoic and Neoproterozoic granitic basement and overlying Neoproterozoic continental-margin sediments. Variably deformed, ferroan and peraluminous metagranitoids compose a major part of AKC and are interlayered with eclogites in its southern and eastern margins. They have geochemical features of post-collisional/intraplate high-K calc-alkaline granites. LA-ICP-MS U-Pb zircon geochronology of three distinct metagranite samples show uniform protolith crystallization ages of ca. 0.96 Ga and uncertain re-crystallization in the Late Neoproterozoic or Early Paleozoic metamorphic event, whereas abundant zircon inheritance indicates older, Mesoproterozoic to Paleoproterozoic crustal substrate during granite generation. The existence of Mesoproterozoic crust is highlighted by finding of distinct metagranitoids with the U-Pb zircon crystallization age of ca. 1.6 Ga. Hafnium isotope signatures (TDMC 2.88-1.85 Ga) of zircons from all lithologies preserved the evidence of reworked Neoarchean to Paleoproterozoic crust, similar to that of the Baidrag block (southern Mongolia), for both Mesoproterozoic and Neoproterozoic rocks. Regardless of the specific lithology, the rocks display indicators of high-pressure metamorphic re-equilibration, including garnet (XCa up to 0.65) + epidote + phengite (Si p.f.u. up to 3.56) ± rutile assemblage in metagranitoids, garnet + phengite (Si p.f.u. up to 3.42) in quartz-rich semi-pelites and garnet + phengite (Si p.f.u. up to 3.39) + medium-Mg chloritoid (XMg up to 0.25) + kyanite + rutile in metapelites. Corresponding P-T conditions recovered from different lithologies reveal incoherent subduction of rocks, which could be shallow for granitic basement (1.1-1.4 GPa and 600-670℃) and clastic metasediments (1.4-1.6 GPa, 570-620℃), but deeper for metapelites (2.1-2.3 GPa, 500-570℃). consistent with that of eclogites, The combined data show that the Alag Khadny complex represents a remnant of a rifted Mesoproterozoic to Neoproterozoic (ca. 1.6-0.96 Ga) continental margin consequently metamorphosed under HP conditions during Late Neoproterozoic-Early Cambrian evolution of the southern Central Asian Orogenic Belt. Acquired P-T estimates imply that high-pressure metagranitoids and metasedimentary rocks equilibrated at different depths, but most likely shared a common subduction-related metamorphic evolution.
2021, 12(3): 101086.
doi: 10.1016/j.gsf.2020.09.015
Abstract:
The hydrochemical composition of surface water and groundwater is a key parameter for understanding the evolution of water and its quality. In particular, little is known about the impact of transferred water on surface water and groundwater. In this study, Baiyangdian Lake was selected as a typical area for extensive groundwater exploration and surface water transfer in the North China Plain. Surface water and groundwater samples were sampled in dry/wet seasons and then analyzed before/after the water transfer, respectively. Generally, surface water and groundwater are extensively hydrologically connected based on hydrochemical evidence. It was found that the hydrochemical composition of the shallow groundwater is affected by the surface water and that the water quality of the deep groundwater is stable. However, inter-aquifer recharge processes from the shallow groundwater to the deep groundwater existed in the anthropogenic region impacted with high nitrate-ion concentrations. Also, the hydrochemical composition of the surface water and groundwater was dominated by rock-weathering and evaporation-precipitation processes. Due to the existence of the deep vadose zone in the alluvial fan, Na+ was exchanged into soil matrices during the leakage of the surface water. In addition, the transferred water resulted in surface water with good quality, and it also played as an important recharge source to groundwater. As the most important water resource for irrigation and drinking, deep groundwater should be paid more attention in the alluvial fan with frequent water transfer and extensive groundwater exploration.
The hydrochemical composition of surface water and groundwater is a key parameter for understanding the evolution of water and its quality. In particular, little is known about the impact of transferred water on surface water and groundwater. In this study, Baiyangdian Lake was selected as a typical area for extensive groundwater exploration and surface water transfer in the North China Plain. Surface water and groundwater samples were sampled in dry/wet seasons and then analyzed before/after the water transfer, respectively. Generally, surface water and groundwater are extensively hydrologically connected based on hydrochemical evidence. It was found that the hydrochemical composition of the shallow groundwater is affected by the surface water and that the water quality of the deep groundwater is stable. However, inter-aquifer recharge processes from the shallow groundwater to the deep groundwater existed in the anthropogenic region impacted with high nitrate-ion concentrations. Also, the hydrochemical composition of the surface water and groundwater was dominated by rock-weathering and evaporation-precipitation processes. Due to the existence of the deep vadose zone in the alluvial fan, Na+ was exchanged into soil matrices during the leakage of the surface water. In addition, the transferred water resulted in surface water with good quality, and it also played as an important recharge source to groundwater. As the most important water resource for irrigation and drinking, deep groundwater should be paid more attention in the alluvial fan with frequent water transfer and extensive groundwater exploration.
2021, 12(3): 101088.
doi: 10.1016/j.gsf.2020.09.017
Abstract:
The Bayanhot Basin is a superimposed basin that experienced multiple-staged tectonic movements; it is in the eastern Alxa Block, adjacent to the North China Craton (NCC) and the North Qilian Orogenic Belt (NQOB). There are well-developed Paleozoic-Cenozoic strata in this basin, and these provide a crucial window to a greater understanding of the amalgamation process and source-to-sink relationships between the Alxa Block and surrounding tectonic units. However, due to intensive post-depositional modification, and lack of subsurface data, several fundamental issues-including the distribution and evolution of the depositional systems, provenance supplies and source-to-sink relationships during the Carboniferous-Permian remain unclear and thus hinder hydrocarbon exploration and limit the geological understanding of this basin. Employing integrated outcrop surveys, new drilling data, and detrital zircon dating, this study examines the paleogeographic distribution and evolution, and provenance characteristics of the Carboniferous-Permian strata in the Bayanhot Basin. Our results show that the Bayanhot Basin experienced a long-term depositional evolution process from transgression to retrogression during the Carboniferous-late Permian. The transgression extent could reach the central basin in the early Carboniferous. The maximum regional transgression occurred in the early Permian and might connect the Qilian and North China seas with each other. Subsequently, a gradual regression followed until the end of the Permian. The northwestern NCC appeared as a paleo-uplift area and served as a sediments provenance area for the Alxa Block at that time. The NCC, Bayanwula Mountain, and NQOB jointly served as major provenances during the Carboniferous-Permian. There was no ocean separation, nor was there an orogenic belt between the Alxa Block and the NCC that provided sediments for both sides during the Carboniferous-Permian. The accretion of the Alxa and North China blocks should have been completed before the Carboniferous period.
The Bayanhot Basin is a superimposed basin that experienced multiple-staged tectonic movements; it is in the eastern Alxa Block, adjacent to the North China Craton (NCC) and the North Qilian Orogenic Belt (NQOB). There are well-developed Paleozoic-Cenozoic strata in this basin, and these provide a crucial window to a greater understanding of the amalgamation process and source-to-sink relationships between the Alxa Block and surrounding tectonic units. However, due to intensive post-depositional modification, and lack of subsurface data, several fundamental issues-including the distribution and evolution of the depositional systems, provenance supplies and source-to-sink relationships during the Carboniferous-Permian remain unclear and thus hinder hydrocarbon exploration and limit the geological understanding of this basin. Employing integrated outcrop surveys, new drilling data, and detrital zircon dating, this study examines the paleogeographic distribution and evolution, and provenance characteristics of the Carboniferous-Permian strata in the Bayanhot Basin. Our results show that the Bayanhot Basin experienced a long-term depositional evolution process from transgression to retrogression during the Carboniferous-late Permian. The transgression extent could reach the central basin in the early Carboniferous. The maximum regional transgression occurred in the early Permian and might connect the Qilian and North China seas with each other. Subsequently, a gradual regression followed until the end of the Permian. The northwestern NCC appeared as a paleo-uplift area and served as a sediments provenance area for the Alxa Block at that time. The NCC, Bayanwula Mountain, and NQOB jointly served as major provenances during the Carboniferous-Permian. There was no ocean separation, nor was there an orogenic belt between the Alxa Block and the NCC that provided sediments for both sides during the Carboniferous-Permian. The accretion of the Alxa and North China blocks should have been completed before the Carboniferous period.
2021, 12(3): 101089.
doi: 10.1016/j.gsf.2020.09.018
Abstract:
3-D geochemical subsurface models, as constructed by spatial interpolation of drill-core assays, are valuable assets across multiple stages of the mineral industry's workflow. However, the accuracy of such models is limited by the spatial sparsity of the underlying drill-core, which samples only a small fraction of the subsurface. This limitation can be alleviated by integrating collocated 3-D models into the interpolation process, such as the 3-D rock property models produced by modern geophysical inversion procedures, provided that they are sufficiently resolved and correlated with the interpolation target. While standard machine learning algorithms are capable of predicting the target property given these data, incorporating spatial autocorrelation and anisotropy in these models is often not possible. We propose a Gaussian process regression model for 3-D geochemical interpolation, where custom kernels are introduced to integrate collocated 3-D rock property models while addressing the trade-off between the spatial proximity of drill-cores and the similarities in their collocated rock properties, as well as the relative degree to which each supporting 3-D model contributes to interpolation. The proposed model was evaluated for 3-D modelling of Mg content in the Kevitsa Ni-Cu-PGE deposit based on drill-core analyses and four 3-D geophysical inversion models. Incorporating the inversion models improved the regression model's likelihood (relative to a purely spatial Gaussian process regression model) when evaluated at held-out test holes, but only for moderate spatial scales (100 m).
3-D geochemical subsurface models, as constructed by spatial interpolation of drill-core assays, are valuable assets across multiple stages of the mineral industry's workflow. However, the accuracy of such models is limited by the spatial sparsity of the underlying drill-core, which samples only a small fraction of the subsurface. This limitation can be alleviated by integrating collocated 3-D models into the interpolation process, such as the 3-D rock property models produced by modern geophysical inversion procedures, provided that they are sufficiently resolved and correlated with the interpolation target. While standard machine learning algorithms are capable of predicting the target property given these data, incorporating spatial autocorrelation and anisotropy in these models is often not possible. We propose a Gaussian process regression model for 3-D geochemical interpolation, where custom kernels are introduced to integrate collocated 3-D rock property models while addressing the trade-off between the spatial proximity of drill-cores and the similarities in their collocated rock properties, as well as the relative degree to which each supporting 3-D model contributes to interpolation. The proposed model was evaluated for 3-D modelling of Mg content in the Kevitsa Ni-Cu-PGE deposit based on drill-core analyses and four 3-D geophysical inversion models. Incorporating the inversion models improved the regression model's likelihood (relative to a purely spatial Gaussian process regression model) when evaluated at held-out test holes, but only for moderate spatial scales (100 m).
2021, 12(3): 101100.
doi: 10.1016/j.gsf.2020.10.007
Abstract:
Flash floods are responsible for loss of life and considerable property damage in many countries. Flood susceptibility maps contribute to flood risk reduction in areas that are prone to this hazard if appropriately used by landuse planners and emergency managers. The main objective of this study is to prepare an accurate flood susceptibility map for the Haraz watershed in Iran using a novel modeling approach (DBPGA) based on Deep Belief Network (DBN) with Back Propagation (BP) algorithm optimized by the Genetic Algorithm (GA). For this task, a database comprising ten conditioning factors and 194 flood locations was created using the One-R Attribute Evaluation (ORAE) technique. Various well-known machine learning and optimization algorithms were used as benchmarks to compare the prediction accuracy of the proposed model. Statistical metrics include sensitivity, specificity accuracy, root mean square error (RMSE), and area under the receiver operatic characteristic curve (AUC) were used to assess the validity of the proposed model. The result shows that the proposed model has the highest goodness-of-fit (AUC=0.989) and prediction accuracy (AUC=0.985), and based on the validation dataset it outperforms benchmark models including LR (0.885), LMT (0.934), BLR (0.936), ADT (0.976), NBT (0.974), REPTree (0.811), ANFIS-BAT (0.944), ANFIS-CA (0.921), ANFIS-IWO (0.939), ANFIS-ICA (0.947), and ANFIS-FA (0.917). We conclude that the DBPGA model is an excellent alternative tool for predicting flash flood susceptibility for other regions prone to flash floods.
Flash floods are responsible for loss of life and considerable property damage in many countries. Flood susceptibility maps contribute to flood risk reduction in areas that are prone to this hazard if appropriately used by landuse planners and emergency managers. The main objective of this study is to prepare an accurate flood susceptibility map for the Haraz watershed in Iran using a novel modeling approach (DBPGA) based on Deep Belief Network (DBN) with Back Propagation (BP) algorithm optimized by the Genetic Algorithm (GA). For this task, a database comprising ten conditioning factors and 194 flood locations was created using the One-R Attribute Evaluation (ORAE) technique. Various well-known machine learning and optimization algorithms were used as benchmarks to compare the prediction accuracy of the proposed model. Statistical metrics include sensitivity, specificity accuracy, root mean square error (RMSE), and area under the receiver operatic characteristic curve (AUC) were used to assess the validity of the proposed model. The result shows that the proposed model has the highest goodness-of-fit (AUC=0.989) and prediction accuracy (AUC=0.985), and based on the validation dataset it outperforms benchmark models including LR (0.885), LMT (0.934), BLR (0.936), ADT (0.976), NBT (0.974), REPTree (0.811), ANFIS-BAT (0.944), ANFIS-CA (0.921), ANFIS-IWO (0.939), ANFIS-ICA (0.947), and ANFIS-FA (0.917). We conclude that the DBPGA model is an excellent alternative tool for predicting flash flood susceptibility for other regions prone to flash floods.
2021, 12(3): 101095.
doi: 10.1016/j.gsf.2020.09.022
Abstract:
This work developed models to identify optimal spatial distribution of emergency evacuation centers (EECs) such as schools, colleges, hospitals, and fire stations to improve flood emergency planning in the Sylhet region of northeastern Bangladesh. The use of location-allocation models (LAMs) for evacuation in regard to flood victims is essential to minimize disaster risk. In the first step, flood susceptibility maps were developed using machine learning models (MLMs), including:Levenberg-Marquardt back propagation (LM-BP) neural network and decision trees (DT) and multi-criteria decision making (MCDM) method. Performance of the MLMs and MCDM techniques were assessed considering the area under the receiver operating characteristic (AUROC) curve. Mathematical approaches in a geographic information system (GIS) for four well-known LAM problems affecting emergency rescue time are proposed:maximal covering location problem (MCLP), the maximize attendance (MA), p-median problem (PMP), and the location set covering problem (LSCP). The results showed that existing EECs were not optimally distributed, and that some areas were not adequately served by EECs (i.e., not all demand points could be reached within a 60-min travel time). We concluded that the proposed models can be used to improve planning of the distribution of EECs, and that application of the models could contribute to reducing human casualties, property losses, and improve emergency operation.
This work developed models to identify optimal spatial distribution of emergency evacuation centers (EECs) such as schools, colleges, hospitals, and fire stations to improve flood emergency planning in the Sylhet region of northeastern Bangladesh. The use of location-allocation models (LAMs) for evacuation in regard to flood victims is essential to minimize disaster risk. In the first step, flood susceptibility maps were developed using machine learning models (MLMs), including:Levenberg-Marquardt back propagation (LM-BP) neural network and decision trees (DT) and multi-criteria decision making (MCDM) method. Performance of the MLMs and MCDM techniques were assessed considering the area under the receiver operating characteristic (AUROC) curve. Mathematical approaches in a geographic information system (GIS) for four well-known LAM problems affecting emergency rescue time are proposed:maximal covering location problem (MCLP), the maximize attendance (MA), p-median problem (PMP), and the location set covering problem (LSCP). The results showed that existing EECs were not optimally distributed, and that some areas were not adequately served by EECs (i.e., not all demand points could be reached within a 60-min travel time). We concluded that the proposed models can be used to improve planning of the distribution of EECs, and that application of the models could contribute to reducing human casualties, property losses, and improve emergency operation.
2021, 12(3): 101074.
doi: 10.1016/j.gsf.2020.09.005
Abstract:
Despite two decades of major advances in the field of thermochronological modeling, state-of-the-art numerical implementations still rely mostly on burial and exhumation processes to explain radiometric measurements. Even though such an approach has proved valuable, failing to account for other first-order geological variables has led to misinterpretations and therefore, calls for a refinement. In this study a new version of the Fetkin (finite element temperature kinematics, Ecopetrol) program is presented. Its new algorithm couples time-dependent hydrological and thermal calculations, thus rendering thermochronological ages that, instead of being solely dependent on the kinematical evolution of a system, conditioning by the fluid flow is also present. In contrast with previous thermochronological models, this work considers the influence of effective stress on rock properties (porosity and permeability) and therefore, in thermal conductivity. Sensitivity analyses addressing relevant geological questions show not only the versatility of the code but also, new perspectives on forward low-temperature thermochronological modeling. Groundwater circulation through pure-sandstone settings produce colder thermal architectures than those obtained in impermeable domains. Differences in cooling ages from models with and without fluid circulation are up to 5 Myr. A 4-fold variation in thrusting rates (0.5km/Myr to 2km/Myr) produces a 15-Myr difference in cooling ages in models with fluid flow, which contrasts to much lower differences, only 2 Myr, in domains without (or minimal) fluid circulation. 2D thermal solutions in fold-bend-fold thrust belts composed of sandstones remain static despite substantial relief development by kinematic folding. A case-study from Western Argentina, in the Andean Precordillera, confirms the plausibility of the numerical algorithm here posed and raises new questions on the first-order thermal controls in settings under deformation.
2021, 12(3): 101091.
doi: 10.1016/j.gsf.2020.09.020
Abstract:
A reliable and accurate prediction of the tunnel boring machine (TBM) performance can assist in minimizing the relevant risks of high capital costs and in scheduling tunneling projects. This research aims to develop six hybrid models of extreme gradient boosting (XGB) which are optimized by gray wolf optimization (GWO), particle swarm optimization (PSO), social spider optimization (SSO), sine cosine algorithm (SCA), multi verse optimization (MVO) and moth flame optimization (MFO), for estimation of the TBM penetration rate (PR). To do this, a comprehensive database with 1286 data samples was established where seven parameters including the rock quality designation, the rock mass rating, Brazilian tensile strength (BTS), rock mass weathering, the uniaxial compressive strength (UCS), revolution per minute and trust force per cutter (TFC), were set as inputs and TBM PR was selected as model output. Together with the mentioned six hybrid models, four single models i.e., artificial neural network, random forest regression, XGB and support vector regression were also built to estimate TBM PR for comparison purposes. These models were designed conducting several parametric studies on their most important parameters and then, their performance capacities were assessed through the use of root mean square error, coefficient of determination, mean absolute percentage error, and a10-index. Results of this study confirmed that the best predictive model of PR goes to the PSO-XGB technique with system error of (0.1453, and 0.1325), R2 of (0.951, and 0.951), mean absolute percentage error (4.0689, and 3.8115), and a10-index of (0.9348, and 0.9496) in training and testing phases, respectively. The developed hybrid PSO-XGB can be introduced as an accurate, powerful and applicable technique in the field of TBM performance prediction. By conducting sensitivity analysis, it was found that UCS, BTS and TFC have the deepest impacts on the TBM PR.
A reliable and accurate prediction of the tunnel boring machine (TBM) performance can assist in minimizing the relevant risks of high capital costs and in scheduling tunneling projects. This research aims to develop six hybrid models of extreme gradient boosting (XGB) which are optimized by gray wolf optimization (GWO), particle swarm optimization (PSO), social spider optimization (SSO), sine cosine algorithm (SCA), multi verse optimization (MVO) and moth flame optimization (MFO), for estimation of the TBM penetration rate (PR). To do this, a comprehensive database with 1286 data samples was established where seven parameters including the rock quality designation, the rock mass rating, Brazilian tensile strength (BTS), rock mass weathering, the uniaxial compressive strength (UCS), revolution per minute and trust force per cutter (TFC), were set as inputs and TBM PR was selected as model output. Together with the mentioned six hybrid models, four single models i.e., artificial neural network, random forest regression, XGB and support vector regression were also built to estimate TBM PR for comparison purposes. These models were designed conducting several parametric studies on their most important parameters and then, their performance capacities were assessed through the use of root mean square error, coefficient of determination, mean absolute percentage error, and a10-index. Results of this study confirmed that the best predictive model of PR goes to the PSO-XGB technique with system error of (0.1453, and 0.1325), R2 of (0.951, and 0.951), mean absolute percentage error (4.0689, and 3.8115), and a10-index of (0.9348, and 0.9496) in training and testing phases, respectively. The developed hybrid PSO-XGB can be introduced as an accurate, powerful and applicable technique in the field of TBM performance prediction. By conducting sensitivity analysis, it was found that UCS, BTS and TFC have the deepest impacts on the TBM PR.
2021, 12(3): 101092.
doi: 10.1016/j.gsf.2020.09.021
Abstract:
The Bálvány North Permian-Triassic boundary sediments were deposited on a carbonate platform in the tropical part of the western PaleoTethys ocean. The overall elemental geochemistry of the detailed two-metre-thick section across the boundary that we studied shows that the clastic content of the sediments came from dominantly silica-rich continental sources though with some more silica-poor inputs in the uppermost Permian and lowest Triassic limestones as shown by Ni/Al and Nb/Ta ratios. These inputs bracket, but do not coincide with, the main extinctions and associated C, O and S changes. Increased aridity at the Permian-Triassic boundary with increased wind abrasion of suitable Ti-bearing heavy minerals accounts for both the high Ti/Al and Ti/Zr ratios. Various geochemical redox proxies suggest mainly oxic depositional conditions, with episodes of anoxia, but with little systematic variation across the Permian-Triassic extinction boundary. The lack of consistent element geochemical changes across the Permian-Triassic boundary occur not only in adjacent shallower-water marine sections, and in other marine sections along the SW Tethys margin such as the Salt Range sections in Pakistan, but also in deeper shelf and oceanic sections, and in non-marine African and European continental sediments. In the absence of significant changes in physical environments, chemical changes in the atmosphere and oceans, reflected in various isotopic changes, drove the Permian-Triassic extinctions.
The Bálvány North Permian-Triassic boundary sediments were deposited on a carbonate platform in the tropical part of the western PaleoTethys ocean. The overall elemental geochemistry of the detailed two-metre-thick section across the boundary that we studied shows that the clastic content of the sediments came from dominantly silica-rich continental sources though with some more silica-poor inputs in the uppermost Permian and lowest Triassic limestones as shown by Ni/Al and Nb/Ta ratios. These inputs bracket, but do not coincide with, the main extinctions and associated C, O and S changes. Increased aridity at the Permian-Triassic boundary with increased wind abrasion of suitable Ti-bearing heavy minerals accounts for both the high Ti/Al and Ti/Zr ratios. Various geochemical redox proxies suggest mainly oxic depositional conditions, with episodes of anoxia, but with little systematic variation across the Permian-Triassic extinction boundary. The lack of consistent element geochemical changes across the Permian-Triassic boundary occur not only in adjacent shallower-water marine sections, and in other marine sections along the SW Tethys margin such as the Salt Range sections in Pakistan, but also in deeper shelf and oceanic sections, and in non-marine African and European continental sediments. In the absence of significant changes in physical environments, chemical changes in the atmosphere and oceans, reflected in various isotopic changes, drove the Permian-Triassic extinctions.
2021, 12(3): 101093.
doi: 10.1016/j.gsf.2020.10.001
Abstract:
The work investigates the major solute chemistry of groundwater and fluoride enrichment (F-) in the shallow phreatic aquifer of Odisha. The study also interprets the hydrogeochemical processes of solute acquisition and the genetic behavior of groundwater F- contamination. A total of 1105 groundwater samples collected from across the state from different hydro-geomorphic settings have been analyzed for the major solutes and F- content. Groundwater is alkaline in nature (range of pH:6.6-8.7; ave.:7.9) predominated by moderately hard to very hard types. Average cation and anion chemistry stand in the orders of Ca2+ > Na+ > Mg2+ > K+ and HCO3- > Cl- > SO42- > CO32- respectively. The average mineralization is low (319 mg/L). The primary water types are Ca-Mg-HCO3 and Ca-Mg-Cl-HCO3, followed by Na-Cl, Ca-Mg-Cl, and Na-Ca-Mg-HCO3-Cl. Silicate-halite dissolution and reverse ion exchange are the significant processes of solute acquisition.Both the geogenic as well as the anthropogenic sources contribute to the groundwater fluoride contamination, etc. The ratio of Na+/Ca2+ > 1.0 comprises Na-HCO3 (Cl) water types with F- > 1.0 mg/L (range 1.0-3.5 mg/L) where the F- bears geogenic source. Positive relations exist between F- and pH, Na+, TDS, and HCO3-. It also reflects a perfect Na-TDS correlation (0.85). The ratio of Na+/Ca2+ < 1.0 segregates the sample population (F- range:1.0-4.0 mg/L) with the F derived from anthropogenic sources. Such water types include Ca-Mg-HCO3 (Cl) varieties which are recently recharged meteoritic water types. The F- levels exhibit poor and negative correlations with the solutes in groundwater. The Na-TDS relation remains poor (0.12). In contrast, the TDS levels show strong correlations with Ca2+ (0.91), Mg2+ (0.80) and even Cl- (0.91). The majority of the monitoring points with the anthropogenic sources of groundwater F- are clustered in the Hirakud Canal Command area in the western parts of the state, indicating the role of irrigation return flow in the F- contamination.
The work investigates the major solute chemistry of groundwater and fluoride enrichment (F-) in the shallow phreatic aquifer of Odisha. The study also interprets the hydrogeochemical processes of solute acquisition and the genetic behavior of groundwater F- contamination. A total of 1105 groundwater samples collected from across the state from different hydro-geomorphic settings have been analyzed for the major solutes and F- content. Groundwater is alkaline in nature (range of pH:6.6-8.7; ave.:7.9) predominated by moderately hard to very hard types. Average cation and anion chemistry stand in the orders of Ca2+ > Na+ > Mg2+ > K+ and HCO3- > Cl- > SO42- > CO32- respectively. The average mineralization is low (319 mg/L). The primary water types are Ca-Mg-HCO3 and Ca-Mg-Cl-HCO3, followed by Na-Cl, Ca-Mg-Cl, and Na-Ca-Mg-HCO3-Cl. Silicate-halite dissolution and reverse ion exchange are the significant processes of solute acquisition.Both the geogenic as well as the anthropogenic sources contribute to the groundwater fluoride contamination, etc. The ratio of Na+/Ca2+ > 1.0 comprises Na-HCO3 (Cl) water types with F- > 1.0 mg/L (range 1.0-3.5 mg/L) where the F- bears geogenic source. Positive relations exist between F- and pH, Na+, TDS, and HCO3-. It also reflects a perfect Na-TDS correlation (0.85). The ratio of Na+/Ca2+ < 1.0 segregates the sample population (F- range:1.0-4.0 mg/L) with the F derived from anthropogenic sources. Such water types include Ca-Mg-HCO3 (Cl) varieties which are recently recharged meteoritic water types. The F- levels exhibit poor and negative correlations with the solutes in groundwater. The Na-TDS relation remains poor (0.12). In contrast, the TDS levels show strong correlations with Ca2+ (0.91), Mg2+ (0.80) and even Cl- (0.91). The majority of the monitoring points with the anthropogenic sources of groundwater F- are clustered in the Hirakud Canal Command area in the western parts of the state, indicating the role of irrigation return flow in the F- contamination.
2021, 12(3): 101094.
doi: 10.1016/j.gsf.2020.10.002
Abstract:
Zircon is widely used to simulate melt generation, migration and evolution within the crust and mantle. The achievable performance of melt modelling generally depends on the availability of reliable trace element partition coefficients (D). However, a large range of DREE values for zircon from natural samples and experimental studies has been reported, with values spanning up to 3 orders of magnitude. Unfortunately, a gap of knowledge on this variability is evident. In this study we model the crystallization processes of common REE-bearing minerals from granitic melts and show that the measured zircon DREE would be elevated if there is crystallization of REE-enriched minerals subsequent to zircon. Nevertheless, compared to zircon DREE values measured from experimental studies, this mechanism appears to have a less significant influence on those from natural granite samples since the quantity of crystallized REE-enriched minerals is very low in natural magmatic systems and/or most of them crystallize prior to zircon. Combined with recently published studies, this work supports that analysis of natural zircon/host groundmass pairs provides more robust DREE values applicable to natural systems than those measured from experimental studies, which can be used to constrain the provenance of detrital zircons.
Zircon is widely used to simulate melt generation, migration and evolution within the crust and mantle. The achievable performance of melt modelling generally depends on the availability of reliable trace element partition coefficients (D). However, a large range of DREE values for zircon from natural samples and experimental studies has been reported, with values spanning up to 3 orders of magnitude. Unfortunately, a gap of knowledge on this variability is evident. In this study we model the crystallization processes of common REE-bearing minerals from granitic melts and show that the measured zircon DREE would be elevated if there is crystallization of REE-enriched minerals subsequent to zircon. Nevertheless, compared to zircon DREE values measured from experimental studies, this mechanism appears to have a less significant influence on those from natural granite samples since the quantity of crystallized REE-enriched minerals is very low in natural magmatic systems and/or most of them crystallize prior to zircon. Combined with recently published studies, this work supports that analysis of natural zircon/host groundmass pairs provides more robust DREE values applicable to natural systems than those measured from experimental studies, which can be used to constrain the provenance of detrital zircons.
2021, 12(3): 101101.
doi: 10.1016/j.gsf.2020.11.001
Abstract:
The Merensky Reef hosts one of the largest PGE resources globally. It has been exploited for nearly 100 years, yet its origin remains unresolved. In the present study, we characterised eight samples of the reef at four localities in the western Bushveld Complex using micro-X-ray fluorescence and field emission scanning electron microscopy. Our results indicate that the Merensky Reef formed through a range of diverse processes. Textures exhibited by chromite grains at the base of the reef are consistent with supercooling and in situ growth. The local thickening of the Merensky chromitite layers within troughs in the floor rocks is most readily explained by granular flow. Annealing and deformation textures in pyroxenes of the Merensky pegmatoid bear testament to recrystallisation and deformation. The footwall rocks to the reef contain disseminations of PGE rich sulphides as well as olivine grains with peritectic reaction rims along their upper margins suggesting reactive downward flow of silicate and sulphide melts. Olivine-hosted melt inclusions containing Cl-rich apatite, sodic plagioclase, and phlogopite suggest the presence of highly evolved, volatile-rich melts. Pervasive reverse zonation of cumulus plagioclase in the footwall of the reef indicates dissolution or partial melting of plagioclase, possibly triggered by flux of heat, acidic fluids, or hydrous melt. Together, these data suggest that the reef formed through a combination of magmatic, hydrodynamic and hydromagmatic processes.
The Merensky Reef hosts one of the largest PGE resources globally. It has been exploited for nearly 100 years, yet its origin remains unresolved. In the present study, we characterised eight samples of the reef at four localities in the western Bushveld Complex using micro-X-ray fluorescence and field emission scanning electron microscopy. Our results indicate that the Merensky Reef formed through a range of diverse processes. Textures exhibited by chromite grains at the base of the reef are consistent with supercooling and in situ growth. The local thickening of the Merensky chromitite layers within troughs in the floor rocks is most readily explained by granular flow. Annealing and deformation textures in pyroxenes of the Merensky pegmatoid bear testament to recrystallisation and deformation. The footwall rocks to the reef contain disseminations of PGE rich sulphides as well as olivine grains with peritectic reaction rims along their upper margins suggesting reactive downward flow of silicate and sulphide melts. Olivine-hosted melt inclusions containing Cl-rich apatite, sodic plagioclase, and phlogopite suggest the presence of highly evolved, volatile-rich melts. Pervasive reverse zonation of cumulus plagioclase in the footwall of the reef indicates dissolution or partial melting of plagioclase, possibly triggered by flux of heat, acidic fluids, or hydrous melt. Together, these data suggest that the reef formed through a combination of magmatic, hydrodynamic and hydromagmatic processes.
2021, 12(3): 101102.
doi: 10.1016/j.gsf.2020.11.002
Abstract:
The surface uplift of the Tibetan Plateau (TP) and its geomorphology evolution has triggered aridification of Asia's interior and drainage development at the eastern margin of the plateau. However, how the pre-Cenozoic early growth histories of the TP impact the drainage system and climate is poorly constrained. The Late Mesozoic Lacustrine evaporite-bearing basins on the eastern margin of the TP record significant information on the uplift of the source terranes, source-to-sink system development and climate change. In this study, we presented detrital zircon U-Pb ages from the Upper Cretaceous Yunlong Formation in the Lanping Basin, as well as Hf isotopic, petrographic, direct statistical, and multidimensional scaling analyses, and use them to characterize the provenance and reconstruct the drainage system. All of the samples have five major age peaks at 200-290 Ma, 400-490 Ma, 750-1000 Ma, 1750-1950 Ma, and 2400-2600 Ma with mostly negative ɛHf(t) values (81%). We infer the sediments are primarily derived from recycled sediments of the Songpan-Garze terrane, and partly from the Sichuan Basin and the Southern Qiangtang terrane, as well as the exposed magmatic rocks of the Yidun Arc and Songpan-Garze terrane. The provenance features of the contemporaneous sediments from the Sichuan, Xichang, Chuxiong, and Simao basins indicate a complex hierarchical drainage pattern on the eastern margin of the TP during the Late Cretaceous. The hierarchical drainage system exhibits a complete gradational cycle of lake-basin types from overfilled freshwater Sichuan Basin through balanced fill saline Xichang Basin and underfilled hypersaline Chuxiong, Lanping, Simao, and Khorat Plateau basins from proximal to distal. The early growth of the TP primarily controlled the drainage and lake-basin evolution by not only causing the uplift and exhumation of the source areas and providing large amounts of clastic material to the proximal sub-drainage areas but also intensifying the aridity and deposition of evaporites.
The surface uplift of the Tibetan Plateau (TP) and its geomorphology evolution has triggered aridification of Asia's interior and drainage development at the eastern margin of the plateau. However, how the pre-Cenozoic early growth histories of the TP impact the drainage system and climate is poorly constrained. The Late Mesozoic Lacustrine evaporite-bearing basins on the eastern margin of the TP record significant information on the uplift of the source terranes, source-to-sink system development and climate change. In this study, we presented detrital zircon U-Pb ages from the Upper Cretaceous Yunlong Formation in the Lanping Basin, as well as Hf isotopic, petrographic, direct statistical, and multidimensional scaling analyses, and use them to characterize the provenance and reconstruct the drainage system. All of the samples have five major age peaks at 200-290 Ma, 400-490 Ma, 750-1000 Ma, 1750-1950 Ma, and 2400-2600 Ma with mostly negative ɛHf(t) values (81%). We infer the sediments are primarily derived from recycled sediments of the Songpan-Garze terrane, and partly from the Sichuan Basin and the Southern Qiangtang terrane, as well as the exposed magmatic rocks of the Yidun Arc and Songpan-Garze terrane. The provenance features of the contemporaneous sediments from the Sichuan, Xichang, Chuxiong, and Simao basins indicate a complex hierarchical drainage pattern on the eastern margin of the TP during the Late Cretaceous. The hierarchical drainage system exhibits a complete gradational cycle of lake-basin types from overfilled freshwater Sichuan Basin through balanced fill saline Xichang Basin and underfilled hypersaline Chuxiong, Lanping, Simao, and Khorat Plateau basins from proximal to distal. The early growth of the TP primarily controlled the drainage and lake-basin evolution by not only causing the uplift and exhumation of the source areas and providing large amounts of clastic material to the proximal sub-drainage areas but also intensifying the aridity and deposition of evaporites.
2021, 12(3): 101082.
doi: 10.1016/j.gsf.2020.09.011
Abstract:
The marginal sea and back-arc basins in the Western Pacific Ocean have become the focus of tectonics due to their unique tectonic location. To understand the deep crustal structure in the back-arc region, we present a 545-km-long active-source ocean bottom seismometer (OBS) wide-angle reflection/refraction profile in the East China Sea. The P wave velocity model shows that the Moho depth rises significantly, from approximately 30 km in the East China Sea shelf to approximately 16 km in the axis of the Okinawa Trough. The lower crustal high-velocity zone (HVZ) in the southern Okinawa Trough, with Vp of 6.8-7.3 km/s, is a remarkable manifestation of the mantle material upwelling and accretion to the lower crust. This confirms that the lower crustal high-velocity mantle accretion is developed in the southern Okinawa Trough. During the process of back-arc extension, the crustal structure of the southern Okinawa Trough is completely invaded and penetrated by the upper mantle material in the axis region. In some areas of the southern central graben, the crust may has broken up and entered the initial stage of seafloor spreading. The discontinuous HVZs in the lower crust in the back-arc region also indicate the migration of spreading centers in the back-arc region since the Cenozoic. The asthenosphere material upwelling in the continent-ocean transition zone is constantly driving the lithosphere eastward for episodic extension, and is causing evident tectonic migration in the Western Pacific back-arc region.
The marginal sea and back-arc basins in the Western Pacific Ocean have become the focus of tectonics due to their unique tectonic location. To understand the deep crustal structure in the back-arc region, we present a 545-km-long active-source ocean bottom seismometer (OBS) wide-angle reflection/refraction profile in the East China Sea. The P wave velocity model shows that the Moho depth rises significantly, from approximately 30 km in the East China Sea shelf to approximately 16 km in the axis of the Okinawa Trough. The lower crustal high-velocity zone (HVZ) in the southern Okinawa Trough, with Vp of 6.8-7.3 km/s, is a remarkable manifestation of the mantle material upwelling and accretion to the lower crust. This confirms that the lower crustal high-velocity mantle accretion is developed in the southern Okinawa Trough. During the process of back-arc extension, the crustal structure of the southern Okinawa Trough is completely invaded and penetrated by the upper mantle material in the axis region. In some areas of the southern central graben, the crust may has broken up and entered the initial stage of seafloor spreading. The discontinuous HVZs in the lower crust in the back-arc region also indicate the migration of spreading centers in the back-arc region since the Cenozoic. The asthenosphere material upwelling in the continent-ocean transition zone is constantly driving the lithosphere eastward for episodic extension, and is causing evident tectonic migration in the Western Pacific back-arc region.
2021, 12(3): 101103.
doi: 10.1016/j.gsf.2020.10.008
Abstract:
The Xingmeng Orogenic Belt evolved through a long-lived orogeny involving multiple episodes of subduction and accretion. However, there is a debate on its tectonic evolution during the Late Paleozoic. Here, we report geochemical, geochronological, and isotopic data from strongly peraluminous granites and gabbro-diorites from the Sunidzuoqi-Xilinhot region. Zircon U-Pb ages suggest that the intrusive rocks were emplaced during the Early Carboniferous (333-322 Ma). The granites exhibit geochemical characteristics similar to S-type granites, with high SiO2 (72.34-76.53 wt.%), Al2O3 (12.45-14.65 wt.%), and A/CNK (1.07-1.16), but depleted Sr, Nb, and Ta contents. They exhibit positive εNd(t) and εHf(t) values (-0.3 to 2.8 and 2.7-5.7, respectively) and young Nd and Hf model ages (TDM2(Nd)=853-1110 Ma and TDM2(Hf)=975-1184 Ma), suggesting that they may be the partial melting products of heterogeneous sources with variable proportions of pelite, psammite, and metabasaltic rocks. The meta-gabbro-diorites from the Maihantaolegai pluton have low SiO2 (47.06-53.49 wt.%) and K2O (0.04-0.99 wt.%) contents, and demonstrate slight light rare earth element (REE) depletion in the chondrite-normalized REE diagrams. They have high zircon εHf(t) values (14.41-17.34) and young Hf model ages (TDM2(Hf)=230-418 Ma), indicating a more depleted mantle source. The variations of the Sm/Yb and La/Sm ratios can thus be used to assess the melting degree of the mantle source from 5% to 20%, suggesting a quite shallow mantle melting zone. We propose that the petrogenesis and distribution of the strongly peraluminous granites and gabbro-diorites, as well as the tectonic architecture of the region, can be explained by a ridge subduction model. Based on these results, and previous studies, we suggest a southward ridge subduction model for the Sunidzuoqi-Xilinhot region.
The Xingmeng Orogenic Belt evolved through a long-lived orogeny involving multiple episodes of subduction and accretion. However, there is a debate on its tectonic evolution during the Late Paleozoic. Here, we report geochemical, geochronological, and isotopic data from strongly peraluminous granites and gabbro-diorites from the Sunidzuoqi-Xilinhot region. Zircon U-Pb ages suggest that the intrusive rocks were emplaced during the Early Carboniferous (333-322 Ma). The granites exhibit geochemical characteristics similar to S-type granites, with high SiO2 (72.34-76.53 wt.%), Al2O3 (12.45-14.65 wt.%), and A/CNK (1.07-1.16), but depleted Sr, Nb, and Ta contents. They exhibit positive εNd(t) and εHf(t) values (-0.3 to 2.8 and 2.7-5.7, respectively) and young Nd and Hf model ages (TDM2(Nd)=853-1110 Ma and TDM2(Hf)=975-1184 Ma), suggesting that they may be the partial melting products of heterogeneous sources with variable proportions of pelite, psammite, and metabasaltic rocks. The meta-gabbro-diorites from the Maihantaolegai pluton have low SiO2 (47.06-53.49 wt.%) and K2O (0.04-0.99 wt.%) contents, and demonstrate slight light rare earth element (REE) depletion in the chondrite-normalized REE diagrams. They have high zircon εHf(t) values (14.41-17.34) and young Hf model ages (TDM2(Hf)=230-418 Ma), indicating a more depleted mantle source. The variations of the Sm/Yb and La/Sm ratios can thus be used to assess the melting degree of the mantle source from 5% to 20%, suggesting a quite shallow mantle melting zone. We propose that the petrogenesis and distribution of the strongly peraluminous granites and gabbro-diorites, as well as the tectonic architecture of the region, can be explained by a ridge subduction model. Based on these results, and previous studies, we suggest a southward ridge subduction model for the Sunidzuoqi-Xilinhot region.
2021, 12(3): 101105.
doi: 10.1016/j.gsf.2020.11.003
Abstract:
Improving the accuracy of flood prediction and mapping is crucial for reducing damage resulting from flood events. In this study, we proposed and validated three ensemble models based on the Best First Decision Tree (BFT) and the Bagging (Bagging-BFT), Decorate (Bagging-BFT), and Random Subspace (RSS-BFT) ensemble learning techniques for an improved prediction of flood susceptibility in a spatially-explicit manner. A total number of 126 historical flood events from the Nghe An Province (Vietnam) were connected to a set of 10 flood influencing factors (slope, elevation, aspect, curvature, river density, distance from rivers, flow direction, geology, soil, and land use) for generating the training and validation datasets. The models were validated via several performance metrics that demonstrated the capability of all three ensemble models in elucidating the underlying pattern of flood occurrences within the research area and predicting the probability of future flood events. Based on the Area Under the receiver operating characteristic Curve (AUC), the ensemble Decorate-BFT model that achieved an AUC value of 0.989 was identified as the superior model over the RSS-BFT (AUC = 0.982) and Bagging-BFT (AUC = 0.967) models. A comparison between the performance of the models and the models previously reported in the literature confirmed that our ensemble models provided a reliable estimate of flood susceptibilities and their resulting susceptibility maps are trustful for flood early warning systems as well as development of mitigation plans.
Improving the accuracy of flood prediction and mapping is crucial for reducing damage resulting from flood events. In this study, we proposed and validated three ensemble models based on the Best First Decision Tree (BFT) and the Bagging (Bagging-BFT), Decorate (Bagging-BFT), and Random Subspace (RSS-BFT) ensemble learning techniques for an improved prediction of flood susceptibility in a spatially-explicit manner. A total number of 126 historical flood events from the Nghe An Province (Vietnam) were connected to a set of 10 flood influencing factors (slope, elevation, aspect, curvature, river density, distance from rivers, flow direction, geology, soil, and land use) for generating the training and validation datasets. The models were validated via several performance metrics that demonstrated the capability of all three ensemble models in elucidating the underlying pattern of flood occurrences within the research area and predicting the probability of future flood events. Based on the Area Under the receiver operating characteristic Curve (AUC), the ensemble Decorate-BFT model that achieved an AUC value of 0.989 was identified as the superior model over the RSS-BFT (AUC = 0.982) and Bagging-BFT (AUC = 0.967) models. A comparison between the performance of the models and the models previously reported in the literature confirmed that our ensemble models provided a reliable estimate of flood susceptibilities and their resulting susceptibility maps are trustful for flood early warning systems as well as development of mitigation plans.
2021, 12(3): 101107.
doi: 10.1016/j.gsf.2020.11.004
Abstract:
Mesozoic sedimentary units within the Nanzhao and Mashiping basins record the paleogeographic and tectonic evolution of the Qinling Orogen (QO). This study uses new detrital zircon U-Pb ages and Hf isotopic data to constrain the timing of deposition and provenance of the Taishanmiao, Taizishan, Nanzhao, and Mashiping formations of the North Qinling Orogen (NQO). The detrital zircons can be split by age peaks into five major groups, including Early Cretaceous, Late Triassic, Early Paleozoic, Neoproterozoic and Paleoproterozoic age peaks. On the basis of the youngest zircon ages and age-diagnostic fossils, we conclude that the Taishanmiao (youngest age of 234 Ma) and Taizishan (216 Ma) formations were deposited during the Late Triassic, whereas the Nanzhao Formation (110 Ma) was deposited during the Early Cretaceous rather than the Late Jurassic as previously thought. The Mashiping Formation (110 Ma) was also deposited during the Early Cretaceous. Combined with zircon Hf isotopic compositions, zircons from Late Triassic units were generally derived from the NQO, South Qinling Orogen (SQO), and North China Craton (NCC), with minor amounts derived from the Xing-Meng Orogenic Belt. The sediments within the Nanzhao Formation were mainly derived from the QO, with a minor contribution from the NCC. The Early Cretaceous conglomerates of the Mashiping Formation were generally derived from recycled earlier detritus. This implies that Late Triassic deposition was related to the final closure of the Mianlue Ocean, whereas Early Cretaceous deposition was correlated to the continued intercontinental subduction of the Yangtze Craton beneath the QO. The change in provenance within these Mesozoic sediments suggests the QO underwent two periods of significant uplift, which was a process generated sediments that were deposited in a series of basins of this area.
Mesozoic sedimentary units within the Nanzhao and Mashiping basins record the paleogeographic and tectonic evolution of the Qinling Orogen (QO). This study uses new detrital zircon U-Pb ages and Hf isotopic data to constrain the timing of deposition and provenance of the Taishanmiao, Taizishan, Nanzhao, and Mashiping formations of the North Qinling Orogen (NQO). The detrital zircons can be split by age peaks into five major groups, including Early Cretaceous, Late Triassic, Early Paleozoic, Neoproterozoic and Paleoproterozoic age peaks. On the basis of the youngest zircon ages and age-diagnostic fossils, we conclude that the Taishanmiao (youngest age of 234 Ma) and Taizishan (216 Ma) formations were deposited during the Late Triassic, whereas the Nanzhao Formation (110 Ma) was deposited during the Early Cretaceous rather than the Late Jurassic as previously thought. The Mashiping Formation (110 Ma) was also deposited during the Early Cretaceous. Combined with zircon Hf isotopic compositions, zircons from Late Triassic units were generally derived from the NQO, South Qinling Orogen (SQO), and North China Craton (NCC), with minor amounts derived from the Xing-Meng Orogenic Belt. The sediments within the Nanzhao Formation were mainly derived from the QO, with a minor contribution from the NCC. The Early Cretaceous conglomerates of the Mashiping Formation were generally derived from recycled earlier detritus. This implies that Late Triassic deposition was related to the final closure of the Mianlue Ocean, whereas Early Cretaceous deposition was correlated to the continued intercontinental subduction of the Yangtze Craton beneath the QO. The change in provenance within these Mesozoic sediments suggests the QO underwent two periods of significant uplift, which was a process generated sediments that were deposited in a series of basins of this area.
2021, 12(3): 101117.
doi: 10.1016/j.gsf.2020.12.002
Abstract:
Seamounts on the drifting oceanic crust are inevitably carried by plate motions and eventually accreted or subducted. However, the geochemical signatures of the subducted seamounts and the significance of seamount subduction are not well constrained. Hundreds of seamounts have subducted beneath the Philippine Sea Plate following the westward subduction of the Pacific Plate since the Eocene (~52 Ma). The subducted oceanic crust and seamount materials can be exhumed from the mantle depth to the seafloor in the Mariana forearc region by serpentinite mud volcanoes, providing exceptional opportunities to directly study the subducted oceanic crust and seamounts. The International Ocean Discovery Program (IODP) expedition 366 has recovered a few metamorphosed mafic clasts exhumed from the Mariana forearc serpentinite mud volcanoes, e.g., the Fantangisña and Asùt Tesoru seamounts. These mafic clasts have tholeiitic to alkaline affinities with distinct trace elements and Nd-Hf isotopes characteristics, suggesting different provenances and mantle sources. The tholeiites from the Fantangisña Seamount have trace element characteristics typical of mid-ocean ridge basalt. The Pacific-type Hf-Nd isotopic compositions, combined with the greenschist metamorphism of these tholeiites further suggest that they came from the subducted Pacific oceanic crust. The alkali basalts-dolerites from the Fantangisña and Asùt Tesoru seamounts show ocean island basalt (OIB)-like geochemical characteristics. The OIB-like geochemical signatures and the low-grade metamorphism of these alkali basalts-dolerites suggest they came from subducted seamounts that originally formed in an intraplate setting on the Pacific Plate. The Pacific Plate origin of these metabasites suggests they were formed in the Early Cretaceous or earlier.
Two types of OIBs have been recognized from alkali metabasites, one of which is geochemically similar to the HIMU-EMI-type OIBs from the West Pacific Seamount Province, and another is similar to the EMII-type OIBs from the Samoa Island in southern Pacific, with negative Nb-Ta-Ti anomalies and enriched Nd-Hf isotopes. Generally, these alkali metabasites are sourced from the heterogeneous mantle sources that are similar to the present South Pacific Isotopic and Thermal Anomaly. This study provides direct evidence for seamount subduction in the Mariana convergent margins. We suggest seamount subduction is significant to element cycling, mantle heterogeneity, and mantle oxidation in subduction zones.
Seamounts on the drifting oceanic crust are inevitably carried by plate motions and eventually accreted or subducted. However, the geochemical signatures of the subducted seamounts and the significance of seamount subduction are not well constrained. Hundreds of seamounts have subducted beneath the Philippine Sea Plate following the westward subduction of the Pacific Plate since the Eocene (~52 Ma). The subducted oceanic crust and seamount materials can be exhumed from the mantle depth to the seafloor in the Mariana forearc region by serpentinite mud volcanoes, providing exceptional opportunities to directly study the subducted oceanic crust and seamounts. The International Ocean Discovery Program (IODP) expedition 366 has recovered a few metamorphosed mafic clasts exhumed from the Mariana forearc serpentinite mud volcanoes, e.g., the Fantangisña and Asùt Tesoru seamounts. These mafic clasts have tholeiitic to alkaline affinities with distinct trace elements and Nd-Hf isotopes characteristics, suggesting different provenances and mantle sources. The tholeiites from the Fantangisña Seamount have trace element characteristics typical of mid-ocean ridge basalt. The Pacific-type Hf-Nd isotopic compositions, combined with the greenschist metamorphism of these tholeiites further suggest that they came from the subducted Pacific oceanic crust. The alkali basalts-dolerites from the Fantangisña and Asùt Tesoru seamounts show ocean island basalt (OIB)-like geochemical characteristics. The OIB-like geochemical signatures and the low-grade metamorphism of these alkali basalts-dolerites suggest they came from subducted seamounts that originally formed in an intraplate setting on the Pacific Plate. The Pacific Plate origin of these metabasites suggests they were formed in the Early Cretaceous or earlier.
Two types of OIBs have been recognized from alkali metabasites, one of which is geochemically similar to the HIMU-EMI-type OIBs from the West Pacific Seamount Province, and another is similar to the EMII-type OIBs from the Samoa Island in southern Pacific, with negative Nb-Ta-Ti anomalies and enriched Nd-Hf isotopes. Generally, these alkali metabasites are sourced from the heterogeneous mantle sources that are similar to the present South Pacific Isotopic and Thermal Anomaly. This study provides direct evidence for seamount subduction in the Mariana convergent margins. We suggest seamount subduction is significant to element cycling, mantle heterogeneity, and mantle oxidation in subduction zones.
2021, 12(3): 101076.
doi: 10.1016/j.gsf.2020.09.007
Abstract:
Flood probability maps are essential for a range of applications, including land use planning and developing mitigation strategies and early warning systems. This study describes the potential application of two architectures of deep learning neural networks, namely convolutional neural networks (CNN) and recurrent neural networks (RNN), for spatially explicit prediction and mapping of flash flood probability. To develop and validate the predictive models, a geospatial database that contained records for the historical flood events and geo-environmental characteristics of the Golestan Province in northern Iran was constructed. The step-wise weight assessment ratio analysis (SWARA) was employed to investigate the spatial interplay between floods and different influencing factors. The CNN and RNN models were trained using the SWARA weights and validated using the receiver operating characteristics technique. The results showed that the CNN model (AUC=0.832, RMSE=0.144) performed slightly better than the RNN model (AUC=0.814, RMSE=0.181) in predicting future floods. Further, these models demonstrated an improved prediction of floods compared to previous studies that used different models in the same study area. This study showed that the spatially explicit deep learning neural network models are successful in capturing the heterogeneity of spatial patterns of flood probability in the Golestan Province, and the resulting probability maps can be used for the development of mitigation plans in response to the future floods. The general policy implication of our study suggests that design, implementation, and verification of flood early warning systems should be directed to approximately 40% of the land area characterized by high and very susceptibility to flooding.
Flood probability maps are essential for a range of applications, including land use planning and developing mitigation strategies and early warning systems. This study describes the potential application of two architectures of deep learning neural networks, namely convolutional neural networks (CNN) and recurrent neural networks (RNN), for spatially explicit prediction and mapping of flash flood probability. To develop and validate the predictive models, a geospatial database that contained records for the historical flood events and geo-environmental characteristics of the Golestan Province in northern Iran was constructed. The step-wise weight assessment ratio analysis (SWARA) was employed to investigate the spatial interplay between floods and different influencing factors. The CNN and RNN models were trained using the SWARA weights and validated using the receiver operating characteristics technique. The results showed that the CNN model (AUC=0.832, RMSE=0.144) performed slightly better than the RNN model (AUC=0.814, RMSE=0.181) in predicting future floods. Further, these models demonstrated an improved prediction of floods compared to previous studies that used different models in the same study area. This study showed that the spatially explicit deep learning neural network models are successful in capturing the heterogeneity of spatial patterns of flood probability in the Golestan Province, and the resulting probability maps can be used for the development of mitigation plans in response to the future floods. The general policy implication of our study suggests that design, implementation, and verification of flood early warning systems should be directed to approximately 40% of the land area characterized by high and very susceptibility to flooding.
2021, 12(3): 101104.
doi: 10.1016/j.gsf.2020.10.009
Abstract:
In this study, we developed multiple hybrid machine-learning models to address parameter optimization limitations and enhance the spatial prediction of landslide susceptibility models. We created a geographic information system database, and our analysis results were used to prepare a landslide inventory map containing 359 landslide events identified from Google Earth, aerial photographs, and other validated sources. A support vector regression (SVR) machine-learning model was used to divide the landslide inventory into training (70%) and testing (30%) datasets. The landslide susceptibility map was produced using 14 causative factors. We applied the established gray wolf optimization (GWO) algorithm, bat algorithm (BA), and cuckoo optimization algorithm (COA) to fine-tune the parameters of the SVR model to improve its predictive accuracy. The resultant hybrid models, SVR-GWO, SVR-BA, and SVR-COA, were validated in terms of the area under curve (AUC) and root mean square error (RMSE). The AUC values for the SVR-GWO (0.733), SVR-BA (0.724), and SVR-COA (0.738) models indicate their good prediction rates for landslide susceptibility modeling. SVR-COA had the greatest accuracy, with an RMSE of 0.21687, and SVR-BA had the least accuracy, with an RMSE of 0.23046. The three optimized hybrid models outperformed the SVR model (AUC=0.704, RMSE=0.26689), confirming the ability of metaheuristic algorithms to improve model performance.
In this study, we developed multiple hybrid machine-learning models to address parameter optimization limitations and enhance the spatial prediction of landslide susceptibility models. We created a geographic information system database, and our analysis results were used to prepare a landslide inventory map containing 359 landslide events identified from Google Earth, aerial photographs, and other validated sources. A support vector regression (SVR) machine-learning model was used to divide the landslide inventory into training (70%) and testing (30%) datasets. The landslide susceptibility map was produced using 14 causative factors. We applied the established gray wolf optimization (GWO) algorithm, bat algorithm (BA), and cuckoo optimization algorithm (COA) to fine-tune the parameters of the SVR model to improve its predictive accuracy. The resultant hybrid models, SVR-GWO, SVR-BA, and SVR-COA, were validated in terms of the area under curve (AUC) and root mean square error (RMSE). The AUC values for the SVR-GWO (0.733), SVR-BA (0.724), and SVR-COA (0.738) models indicate their good prediction rates for landslide susceptibility modeling. SVR-COA had the greatest accuracy, with an RMSE of 0.21687, and SVR-BA had the least accuracy, with an RMSE of 0.23046. The three optimized hybrid models outperformed the SVR model (AUC=0.704, RMSE=0.26689), confirming the ability of metaheuristic algorithms to improve model performance.
2021, 12(3): 101116.
doi: 10.1016/j.gsf.2020.11.013
Abstract:
The Magushan skarn Cu-Mo deposit is a representative example of the skarn mineralization occurring within the Xuancheng ore district of the Middle-Lower Yangtze River Metallogenic Belt of eastern China. The precise age of an ore deposit is important for understanding the timing of mineralization relative to other geological events in a region and to fully place the formation of a mineral deposit within the geological context of other processes that occur within the study area. Here, we present new molybdenite Re-Os and titanite and andradite garnet U-Pb ages for the Magushan deposit and use these data to outline possible approaches for identifying genetic relationships in geologically complex areas. The spatial and paragenetic relationships between the intrusions, alteration, and mineralization within the study area indicates that the formation of the Magushan deposit is genetically associated with the porphyritic granodiorite. However, this is not always the case, as some areas contain complexly zoned plutons with multiple phases of intrusion or mineralization may be distal from or may not have any clear spatial relationship to a pluton. This means that it may not be possible to determine whether the mineralization formed as a result of single or multiple magmatic/hydrothermal events. As such, the approaches presented in this study provide an approach that allows the identification of any geochronological relationships between mineralization and intrusive events in areas more complex than the study area. Previously published zircon U-Pb data for the mineralization-related porphyritic granodiorite in this area yielded an age of 134.2 ± 1.2 Ma (MSWD=1.4) whereas the Re-Os dating of molybdenite from the study area yielded an isochron age of 137.7 ± 2.5 Ma (MSWD=0.43). The timing of the mineralizing event in the study area was further examined by the dating of magmatic accessory titanite and skarn-related andradite garnet, yielding U-Pb ages of 136.3 ± 2.5 Ma (MSWD=3.2) and 135.9 ± 2.7 Ma (MSWD=2.5), respectively. The dating of magmatic and hydrothermal activity within the Magushan area yields ages around 136 Ma, strongly suggesting that the mineralization in this area formed as a result of the emplacement of the intrusion. The dates presented in this study also provide the first indication of the timing of mineralization within the Xuancheng district. providing evidence of a close genetic relationship between the formation of the mineralization within the Xuancheng district and the Early Cretaceous magmatism that occurred in this area. This in turn suggests that other Early Cretaceous intrusive rocks within this region are likely to be associated with mineralization and should be considered highly prospective for future mineral exploration. This study also indicates that the dating of garnet and titanite can also provide reliable geochronological data and evidence of the timing of mineralization and magmatism, respectively, in areas lacking other dateable minerals (e.g., molybdenite) or where the relationship between mineralization and magmatism is unclear, for example in areas with multiple stages of magmatism, with complexly zoned plutons, and with distal skarn mineralization.
The Magushan skarn Cu-Mo deposit is a representative example of the skarn mineralization occurring within the Xuancheng ore district of the Middle-Lower Yangtze River Metallogenic Belt of eastern China. The precise age of an ore deposit is important for understanding the timing of mineralization relative to other geological events in a region and to fully place the formation of a mineral deposit within the geological context of other processes that occur within the study area. Here, we present new molybdenite Re-Os and titanite and andradite garnet U-Pb ages for the Magushan deposit and use these data to outline possible approaches for identifying genetic relationships in geologically complex areas. The spatial and paragenetic relationships between the intrusions, alteration, and mineralization within the study area indicates that the formation of the Magushan deposit is genetically associated with the porphyritic granodiorite. However, this is not always the case, as some areas contain complexly zoned plutons with multiple phases of intrusion or mineralization may be distal from or may not have any clear spatial relationship to a pluton. This means that it may not be possible to determine whether the mineralization formed as a result of single or multiple magmatic/hydrothermal events. As such, the approaches presented in this study provide an approach that allows the identification of any geochronological relationships between mineralization and intrusive events in areas more complex than the study area. Previously published zircon U-Pb data for the mineralization-related porphyritic granodiorite in this area yielded an age of 134.2 ± 1.2 Ma (MSWD=1.4) whereas the Re-Os dating of molybdenite from the study area yielded an isochron age of 137.7 ± 2.5 Ma (MSWD=0.43). The timing of the mineralizing event in the study area was further examined by the dating of magmatic accessory titanite and skarn-related andradite garnet, yielding U-Pb ages of 136.3 ± 2.5 Ma (MSWD=3.2) and 135.9 ± 2.7 Ma (MSWD=2.5), respectively. The dating of magmatic and hydrothermal activity within the Magushan area yields ages around 136 Ma, strongly suggesting that the mineralization in this area formed as a result of the emplacement of the intrusion. The dates presented in this study also provide the first indication of the timing of mineralization within the Xuancheng district. providing evidence of a close genetic relationship between the formation of the mineralization within the Xuancheng district and the Early Cretaceous magmatism that occurred in this area. This in turn suggests that other Early Cretaceous intrusive rocks within this region are likely to be associated with mineralization and should be considered highly prospective for future mineral exploration. This study also indicates that the dating of garnet and titanite can also provide reliable geochronological data and evidence of the timing of mineralization and magmatism, respectively, in areas lacking other dateable minerals (e.g., molybdenite) or where the relationship between mineralization and magmatism is unclear, for example in areas with multiple stages of magmatism, with complexly zoned plutons, and with distal skarn mineralization.
2021, 12(3): 101114.
doi: 10.1016/j.gsf.2020.11.011
Abstract:
Platinum group elements (PGE) and Re-Os isotopes of mantle peridotites in the Jinshajiang ophiolite (SW China) were investigated in this study, in order to constrain the evolution of the lithospheric mantle beneath the Jinshajiang-Ailaoshan Ocean, which was a branch of the eastern Paleo-Tethys. The Jinshajiang peridotites have whole-rock compositions (e.g., MgO=32.7-38.1 wt.%; Al2O3=0.67-1.30 wt.%) and spinels with moderate Cr# values (0.4-0.6) similar to those of abyssal peridotites, which indicate moderate degrees of partial melting (15%-20%). These peridotites exhibit U-shaped chondrite-normalized REE patterns that could be caused by hydrothermal alteration or melt-rock interaction after mantle melting. In addition, Pd concentrations and (Pd/Ir)N ratios of the Jinshajiang peridotites increases with decreasing Al2O3 concentrations. These negative correlations cannot be explained by simple partial melting but record a melt-rock reaction event after mantle melting. This study therefore demonstrates the efficiency of PGE in detecting the melt-rock reaction process relative to whole-rock major and trace elements. The suprachondritic 187Os/188Os ratios (0.1272-0.1374) further indicate that the later percolating melt derived from a mantle domain with distinct 187Os-enriched isotopic compositions. In comparison with peridotites in the Ailaoshan ophiolite belt, which were not significantly affected by melt percolation, this study further highlights that the lithospheric mantle compositions beneath different segments of the same ocean basin are highly variable and might be controlled by distinct mantle processes in response to different rifting mechanisms.
Platinum group elements (PGE) and Re-Os isotopes of mantle peridotites in the Jinshajiang ophiolite (SW China) were investigated in this study, in order to constrain the evolution of the lithospheric mantle beneath the Jinshajiang-Ailaoshan Ocean, which was a branch of the eastern Paleo-Tethys. The Jinshajiang peridotites have whole-rock compositions (e.g., MgO=32.7-38.1 wt.%; Al2O3=0.67-1.30 wt.%) and spinels with moderate Cr# values (0.4-0.6) similar to those of abyssal peridotites, which indicate moderate degrees of partial melting (15%-20%). These peridotites exhibit U-shaped chondrite-normalized REE patterns that could be caused by hydrothermal alteration or melt-rock interaction after mantle melting. In addition, Pd concentrations and (Pd/Ir)N ratios of the Jinshajiang peridotites increases with decreasing Al2O3 concentrations. These negative correlations cannot be explained by simple partial melting but record a melt-rock reaction event after mantle melting. This study therefore demonstrates the efficiency of PGE in detecting the melt-rock reaction process relative to whole-rock major and trace elements. The suprachondritic 187Os/188Os ratios (0.1272-0.1374) further indicate that the later percolating melt derived from a mantle domain with distinct 187Os-enriched isotopic compositions. In comparison with peridotites in the Ailaoshan ophiolite belt, which were not significantly affected by melt percolation, this study further highlights that the lithospheric mantle compositions beneath different segments of the same ocean basin are highly variable and might be controlled by distinct mantle processes in response to different rifting mechanisms.
2021, 12(3): 101122.
doi: 10.1016/j.gsf.2020.12.004
Abstract:
Previous studies demonstrated that melting, initiated by supercritical fluids in the 375-400℃ range, occurred as part of anthracite metamorphism in the Appalachian Basin. Based on the known behavior of vitrinite at high temperatures and, to a lesser extent, at high pressures, it was determined that the duration of the heating, melting, and resolidification event was about 1 h. In the current study, featureless vitrinite within banded maceral assemblages demonstratesthe intimate association of melted and resolidified vitrinite with anthracite-rank macerals. By analogy with metamorphosed inorganic rocks, such associations represent diadysites and embrechites, i.e., cross-cutting and layered migmatites, respectively. Even though the temperature of formation of the anthracite structures is several hundred℃ lower than that seen in metamorphosed inorganic rocks, anthracites are metamorphic rocks and the nomenclature for metamorphic rocks may be appropriate for coal.
Previous studies demonstrated that melting, initiated by supercritical fluids in the 375-400℃ range, occurred as part of anthracite metamorphism in the Appalachian Basin. Based on the known behavior of vitrinite at high temperatures and, to a lesser extent, at high pressures, it was determined that the duration of the heating, melting, and resolidification event was about 1 h. In the current study, featureless vitrinite within banded maceral assemblages demonstratesthe intimate association of melted and resolidified vitrinite with anthracite-rank macerals. By analogy with metamorphosed inorganic rocks, such associations represent diadysites and embrechites, i.e., cross-cutting and layered migmatites, respectively. Even though the temperature of formation of the anthracite structures is several hundred℃ lower than that seen in metamorphosed inorganic rocks, anthracites are metamorphic rocks and the nomenclature for metamorphic rocks may be appropriate for coal.
2021, 12(3): 101120.
doi: 10.1016/j.gsf.2020.12.003
Abstract:
The late Archean (~3.0-2.5Ga) was a key period of continental growth globally, which is widely considered to reflect the onset of vigorous plate tectonic activity, although related continental growth modes remain contentious. Here we investigate a suite of late Neoarchean metavolcanic rocks from the southwest Qixia area of the Jiaobei terrane in the North China Craton. The rocks in this suite include amphibolites, clinopyroxene amphibolites, and hornblende plagioclase gneisses. We present zircon U-Pb isotopic data which indicate that the protoliths of these rocks formed during ~2549-2511Ma.
The (clinopyroxene) amphibolites correspond to meta-basaltic rocks, with some containing high modal content of titanite. These rocks show moderate to high FeOT (8.96-13.62wt.%) and TiO2 (0.59-1.59wt.%), flat to less fractionated REE patterns, and mildly negative Th, Nb, and Ta anomalies, resembling those of Fe-tholeiites. In addition, they display positive zircon ƐHf(t) values (+2.6 to +8.7), and are devoid of crustal contamination or fractional crystallization. Combined with the low Nb/Yb (mostly <1.60) and (Hf/Sm)N (mostly <0.95), low to moderate Th/Yb (0.08-0.54), and low V/Sc (5.53-9.19) ratios, these basaltic rocks are interpreted to have been derived from a relatively reduced and depleted mantle source that was mildly metasomatized by hydrous fluids. The hornblende plagioclase gneisses are meta-andesitic rocks, and occur interlayered with the basaltic rocks. They are transitional between tholeiitic and calc-alkaline rock series, and show fractionated REE patterns with evidently negative Th, Nb, and Ta anomalies. The depleted zircon ƐHf(t) values (+2.4 to +8.4) and quantitative chemical modeling suggest that the andesitic rocks were most likely generated by injection and mixing of juvenile felsic magmas with the tholeiitic basaltic magmas.
In general, the chemical features and genesis of late Neoarchean meta-basaltic rocks in our study area resemble those of Mariana back-arc basin basalts. Combined with regional geological data, it is proposed that the Jiaobei terrane witnessed late Neoarchean crustal growth under a paired continental arc-back arc setting. On a regional context, we propose two distinct geodynamic mode of late Neoarchean continental growth across North China Craton (particularly the Eastern Block), i.e., (1) arc-continent accretion along northwestern part of the Eastern Block; and (2) paired continental arc-back arc system surrounding the ~3.8-2.7Ga continental nuclei to the southeast.
The late Archean (~3.0-2.5Ga) was a key period of continental growth globally, which is widely considered to reflect the onset of vigorous plate tectonic activity, although related continental growth modes remain contentious. Here we investigate a suite of late Neoarchean metavolcanic rocks from the southwest Qixia area of the Jiaobei terrane in the North China Craton. The rocks in this suite include amphibolites, clinopyroxene amphibolites, and hornblende plagioclase gneisses. We present zircon U-Pb isotopic data which indicate that the protoliths of these rocks formed during ~2549-2511Ma.
The (clinopyroxene) amphibolites correspond to meta-basaltic rocks, with some containing high modal content of titanite. These rocks show moderate to high FeOT (8.96-13.62wt.%) and TiO2 (0.59-1.59wt.%), flat to less fractionated REE patterns, and mildly negative Th, Nb, and Ta anomalies, resembling those of Fe-tholeiites. In addition, they display positive zircon ƐHf(t) values (+2.6 to +8.7), and are devoid of crustal contamination or fractional crystallization. Combined with the low Nb/Yb (mostly <1.60) and (Hf/Sm)N (mostly <0.95), low to moderate Th/Yb (0.08-0.54), and low V/Sc (5.53-9.19) ratios, these basaltic rocks are interpreted to have been derived from a relatively reduced and depleted mantle source that was mildly metasomatized by hydrous fluids. The hornblende plagioclase gneisses are meta-andesitic rocks, and occur interlayered with the basaltic rocks. They are transitional between tholeiitic and calc-alkaline rock series, and show fractionated REE patterns with evidently negative Th, Nb, and Ta anomalies. The depleted zircon ƐHf(t) values (+2.4 to +8.4) and quantitative chemical modeling suggest that the andesitic rocks were most likely generated by injection and mixing of juvenile felsic magmas with the tholeiitic basaltic magmas.
In general, the chemical features and genesis of late Neoarchean meta-basaltic rocks in our study area resemble those of Mariana back-arc basin basalts. Combined with regional geological data, it is proposed that the Jiaobei terrane witnessed late Neoarchean crustal growth under a paired continental arc-back arc setting. On a regional context, we propose two distinct geodynamic mode of late Neoarchean continental growth across North China Craton (particularly the Eastern Block), i.e., (1) arc-continent accretion along northwestern part of the Eastern Block; and (2) paired continental arc-back arc system surrounding the ~3.8-2.7Ga continental nuclei to the southeast.
2021, 12(3): 101108.
doi: 10.1016/j.gsf.2020.11.005
Abstract:
Blasting is well-known as an effective method for fragmenting or moving rock in open-pit mines. To evaluate the quality of blasting, the size of rock distribution is used as a critical criterion in blasting operations. A high percentage of oversized rocks generated by blasting operations can lead to economic and environmental damage. Therefore, this study proposed four novel intelligent models to predict the size of rock distribution in mine blasting in order to optimize blasting parameters, as well as the efficiency of blasting operation in open mines. Accordingly, a nature-inspired algorithm (i.e., firefly algorithm-FFA) and different machine learning algorithms (i.e., gradient boosting machine (GBM), support vector machine (SVM), Gaussian process (GP), and artificial neural network (ANN)) were combined for this aim, abbreviated as FFA-GBM, FFA-SVM, FFA-GP, and FFA-ANN, respectively. Subsequently, predicted results from the abovementioned models were compared with each other using three statistical indicators (e.g., mean absolute error, root-mean-squared error, and correlation coefficient) and color intensity method. For developing and simulating the size of rock in blasting operations, 136 blasting events with their images were collected and analyzed by the Split-Desktop software. In which, 111 events were randomly selected for the development and optimization of the models. Subsequently, the remaining 25 blasting events were applied to confirm the accuracy of the proposed models. Herein, blast design parameters were regarded as input variables to predict the size of rock in blasting operations. Finally, the obtained results revealed that the FFA is a robust optimization algorithm for estimating rock fragmentation in bench blasting. Among the models developed in this study, FFA-GBM provided the highest accuracy in predicting the size of fragmented rocks. The other techniques (i.e., FFA-SVM, FFA-GP, and FFA-ANN) yielded lower computational stability and efficiency. Hence, the FFA-GBM model can be used as a powerful and precise soft computing tool that can be applied to practical engineering cases aiming to improve the quality of blasting and rock fragmentation.
Blasting is well-known as an effective method for fragmenting or moving rock in open-pit mines. To evaluate the quality of blasting, the size of rock distribution is used as a critical criterion in blasting operations. A high percentage of oversized rocks generated by blasting operations can lead to economic and environmental damage. Therefore, this study proposed four novel intelligent models to predict the size of rock distribution in mine blasting in order to optimize blasting parameters, as well as the efficiency of blasting operation in open mines. Accordingly, a nature-inspired algorithm (i.e., firefly algorithm-FFA) and different machine learning algorithms (i.e., gradient boosting machine (GBM), support vector machine (SVM), Gaussian process (GP), and artificial neural network (ANN)) were combined for this aim, abbreviated as FFA-GBM, FFA-SVM, FFA-GP, and FFA-ANN, respectively. Subsequently, predicted results from the abovementioned models were compared with each other using three statistical indicators (e.g., mean absolute error, root-mean-squared error, and correlation coefficient) and color intensity method. For developing and simulating the size of rock in blasting operations, 136 blasting events with their images were collected and analyzed by the Split-Desktop software. In which, 111 events were randomly selected for the development and optimization of the models. Subsequently, the remaining 25 blasting events were applied to confirm the accuracy of the proposed models. Herein, blast design parameters were regarded as input variables to predict the size of rock in blasting operations. Finally, the obtained results revealed that the FFA is a robust optimization algorithm for estimating rock fragmentation in bench blasting. Among the models developed in this study, FFA-GBM provided the highest accuracy in predicting the size of fragmented rocks. The other techniques (i.e., FFA-SVM, FFA-GP, and FFA-ANN) yielded lower computational stability and efficiency. Hence, the FFA-GBM model can be used as a powerful and precise soft computing tool that can be applied to practical engineering cases aiming to improve the quality of blasting and rock fragmentation.
2021, 12(3): 101118.
doi: 10.1016/j.gsf.2020.11.014
Abstract:
Present study reports the PGE-geochemistry of mantle peridotites and Nd-isotope geochemistry of arc related mafic rocks from the Indus Suture Zone (ISZ), western Ladakh. The total PGE concentration of the Shergol and Suru Valley peridotites (∑PGE=96-180 ppb) is much higher than that of the primitive mantle and global ophiolitic mantle peridotites. The studied peridotites show concave upward PGE-distribution patterns with higher palladium-group PGE/Iridium-group PGE ratios (i.e., 0.8-2.9) suggesting that the partial melting is not the sole factor responsible for the evolution of these peridotites. The observed PGE-distribution patterns are distinct from residual/refractory mantle peridotites, which have concave downward or flat PGE-distribution patterns. Relative enrichment of palladium-group PGE as well as other whole-rock incompatible elements (e.g., LILE and LREE) and higher Pd/Ir ratio (1.1-5.9) reflects that these peridotites have experienced fluid/melt interaction in a supra-subduction zone (SSZ) tectonic setting. Also, the Shergol mafic intrusives and Dras mafic volcanics, associated with the studied peridotites, have high 143Nd/144Nd ratios (i.e., 0.512908-0.513078 and 0.512901-0.512977, respectively) and positive εNd(t) (calculated for t=140 Ma) values (i.e., +5.3 to +8.6 and + 5.1 to +6.6, respectively), indicating derivation from depleted mantle sources within an intra-oceanic arc setting, similar to Spongtang and Nidar ophiolites from other parts of Ladakh Himalaya. The transition from SSZ-type Shergol and Suru Valley peridotites to Early Cretaceous tholeiitic Shergol mafic intrusives followed by tholeiitic to calc-alkaline Dras mafic volcanics within the Neo-Tethys Ocean exhibit characteristics of subduction initiation mechanism analogous to the Izu-Bonin-Mariana arc system within western Pacific.
Present study reports the PGE-geochemistry of mantle peridotites and Nd-isotope geochemistry of arc related mafic rocks from the Indus Suture Zone (ISZ), western Ladakh. The total PGE concentration of the Shergol and Suru Valley peridotites (∑PGE=96-180 ppb) is much higher than that of the primitive mantle and global ophiolitic mantle peridotites. The studied peridotites show concave upward PGE-distribution patterns with higher palladium-group PGE/Iridium-group PGE ratios (i.e., 0.8-2.9) suggesting that the partial melting is not the sole factor responsible for the evolution of these peridotites. The observed PGE-distribution patterns are distinct from residual/refractory mantle peridotites, which have concave downward or flat PGE-distribution patterns. Relative enrichment of palladium-group PGE as well as other whole-rock incompatible elements (e.g., LILE and LREE) and higher Pd/Ir ratio (1.1-5.9) reflects that these peridotites have experienced fluid/melt interaction in a supra-subduction zone (SSZ) tectonic setting. Also, the Shergol mafic intrusives and Dras mafic volcanics, associated with the studied peridotites, have high 143Nd/144Nd ratios (i.e., 0.512908-0.513078 and 0.512901-0.512977, respectively) and positive εNd(t) (calculated for t=140 Ma) values (i.e., +5.3 to +8.6 and + 5.1 to +6.6, respectively), indicating derivation from depleted mantle sources within an intra-oceanic arc setting, similar to Spongtang and Nidar ophiolites from other parts of Ladakh Himalaya. The transition from SSZ-type Shergol and Suru Valley peridotites to Early Cretaceous tholeiitic Shergol mafic intrusives followed by tholeiitic to calc-alkaline Dras mafic volcanics within the Neo-Tethys Ocean exhibit characteristics of subduction initiation mechanism analogous to the Izu-Bonin-Mariana arc system within western Pacific.
2021, 12(3): 101106.
doi: 10.1016/j.gsf.2020.12.001
Abstract:
The Durkan Complex is a key tectonic element of the Makran accretionary prism (SE Iran) and it has been interpreted as representing a continental margin succession. We present here a multidisciplinary study of the western Durkan Complex, which is based on new geological, stratigraphic, biostratigraphic data, as well as geochemical data of the volcanic and meta-volcanic rocks forming this complex. Our data show that this complex consists of distinct tectonic slices showing both non-metamorphic and very low-grade metamorphic deformed successions. Stratigraphic and biostratigraphic data allow us to recognize three types of successions. Type-I is composed by a Coniacian-early Campanian pelagic succession with intercalation of pillow lavas and minor volcaniclastic rocks. Type-II succession includes a volcanic sequence passing to a volcano-sedimentary sequence with Cenomanian pelagic limestones, followed by a hemipelagic sequence. This succession is characterized by abundant mass-transport deposits. Type-III succession includes volcanic and volcano-sedimentary sequences, which are stratigraphically covered by a Cenomanian platform succession. The latter is locally followed by a hemipelagic sequence. The volcanic rocks in the different successions show alkaline geochemical affinity, suggesting an origin from an oceanic within-plate setting. Our new results indicate that the western Durkan Complex represents fragments of seamounts tectonically incorporated in the Makran accretionary wedge during the latest Late Cretaceous-Paleocene. We propose that incorporation of seamounts in the frontal prism caused a shortening of the whole convergent margin and possibly contributed to controlling the deformation style in the Makran Accretionary Wedge during Late Cretaceous-Paleocene times.
The Durkan Complex is a key tectonic element of the Makran accretionary prism (SE Iran) and it has been interpreted as representing a continental margin succession. We present here a multidisciplinary study of the western Durkan Complex, which is based on new geological, stratigraphic, biostratigraphic data, as well as geochemical data of the volcanic and meta-volcanic rocks forming this complex. Our data show that this complex consists of distinct tectonic slices showing both non-metamorphic and very low-grade metamorphic deformed successions. Stratigraphic and biostratigraphic data allow us to recognize three types of successions. Type-I is composed by a Coniacian-early Campanian pelagic succession with intercalation of pillow lavas and minor volcaniclastic rocks. Type-II succession includes a volcanic sequence passing to a volcano-sedimentary sequence with Cenomanian pelagic limestones, followed by a hemipelagic sequence. This succession is characterized by abundant mass-transport deposits. Type-III succession includes volcanic and volcano-sedimentary sequences, which are stratigraphically covered by a Cenomanian platform succession. The latter is locally followed by a hemipelagic sequence. The volcanic rocks in the different successions show alkaline geochemical affinity, suggesting an origin from an oceanic within-plate setting. Our new results indicate that the western Durkan Complex represents fragments of seamounts tectonically incorporated in the Makran accretionary wedge during the latest Late Cretaceous-Paleocene. We propose that incorporation of seamounts in the frontal prism caused a shortening of the whole convergent margin and possibly contributed to controlling the deformation style in the Makran Accretionary Wedge during Late Cretaceous-Paleocene times.
2021, 12(3): 101113.
doi: 10.1016/j.gsf.2020.11.010
Abstract:
Spiral garnet porphyroblasts are known to record lengthy periods of deformation and metamorphism by preserving single or multiple FIAs (Foliation Intersection Axis) formed normal to tectonic shortening directions. Thanks to technological advances in X-ray computed micro-tomography (XCMT), FIAs can now be readily determined in relatively large samples in contrast to previous methods that require the preparation of a set of radial vertical and horizontal thin sections of samples. XCMT scanning not only alleviates tedious thin section based procedures but also illuminates the complete internal architecture of a rock sample allowing three-dimensional (3D) quantitative shape analysis of an individual porphyroblast as well as precise measurement of FIAs. We applied the technique to a sample from the Hunza Valley in the Karakoram metamorphic complex (KMC), NW Himalayas, containing numerous garnet porphyroblasts with spiral-shaped inclusion trails. The XCMT imaging reveals an E-W trending FIA within the sample, which is consistent with orthogonal N-S collision of the India-Kohistan Island Arc with Asia. Garnet long axes (XGT) have variable plunges that define a broad sub-vertical maximum and a small sub-horizontal maximum. The XGT principle maxima lie at N-090 and N-120. Smaller maxima lie at N-020 and N-340. Geometric relationships between XGT axes and FIA orientation in the sample suggest that porphyroblast shapes are controlled by the geometry of the lens-shaped microlithons in which they tend to nucleate and grow. The orientation of inclusion trails and matrix foliations in the sample are correlated with three discrete tectono-metamorphic events that respectively produced andalusite, sillimanite and kyanite in the KMC. Late staurolite growth in the sample reveals how the rocks extruded to the surface via a significant role of roll-on tectonics, which can be correlated with the Central Himalayas.
Spiral garnet porphyroblasts are known to record lengthy periods of deformation and metamorphism by preserving single or multiple FIAs (Foliation Intersection Axis) formed normal to tectonic shortening directions. Thanks to technological advances in X-ray computed micro-tomography (XCMT), FIAs can now be readily determined in relatively large samples in contrast to previous methods that require the preparation of a set of radial vertical and horizontal thin sections of samples. XCMT scanning not only alleviates tedious thin section based procedures but also illuminates the complete internal architecture of a rock sample allowing three-dimensional (3D) quantitative shape analysis of an individual porphyroblast as well as precise measurement of FIAs. We applied the technique to a sample from the Hunza Valley in the Karakoram metamorphic complex (KMC), NW Himalayas, containing numerous garnet porphyroblasts with spiral-shaped inclusion trails. The XCMT imaging reveals an E-W trending FIA within the sample, which is consistent with orthogonal N-S collision of the India-Kohistan Island Arc with Asia. Garnet long axes (XGT) have variable plunges that define a broad sub-vertical maximum and a small sub-horizontal maximum. The XGT principle maxima lie at N-090 and N-120. Smaller maxima lie at N-020 and N-340. Geometric relationships between XGT axes and FIA orientation in the sample suggest that porphyroblast shapes are controlled by the geometry of the lens-shaped microlithons in which they tend to nucleate and grow. The orientation of inclusion trails and matrix foliations in the sample are correlated with three discrete tectono-metamorphic events that respectively produced andalusite, sillimanite and kyanite in the KMC. Late staurolite growth in the sample reveals how the rocks extruded to the surface via a significant role of roll-on tectonics, which can be correlated with the Central Himalayas.
2021, 12(3): 101110.
doi: 10.1016/j.gsf.2020.11.007
Abstract:
Earthquake prediction is currently the most crucial task required for the probability, hazard, risk mapping, and mitigation purposes. Earthquake prediction attracts the researchers' attention from both academia and industries. Traditionally, the risk assessment approaches have used various traditional and machine learning models. However, deep learning techniques have been rarely tested for earthquake probability mapping. Therefore, this study develops a convolutional neural network (CNN) model for earthquake probability assessment in NE India. Then conducts vulnerability using analytical hierarchy process (AHP), Venn's intersection theory for hazard, and integrated model for risk mapping. A prediction of classification task was performed in which the model predicts magnitudes more than 4 Mw that considers nine indicators. Prediction classification results and intensity variation were then used for probability and hazard mapping, respectively. Finally, earthquake risk map was produced by multiplying hazard, vulnerability, and coping capacity. The vulnerability was prepared by using six vulnerable factors, and the coping capacity was estimated by using the number of hospitals and associated variables, including budget available for disaster management. The CNN model for a probability distribution is a robust technique that provides good accuracy. Results show that CNN is superior to the other algorithms, which completed the classification prediction task with an accuracy of 0.94, precision of 0.98, recall of 0.85, and F1 score of 0.91. These indicators were used for probability mapping, and the total area of hazard (21,412.94 km2), vulnerability (480.98 km2), and risk (34,586.10 km2) was estimated.
Earthquake prediction is currently the most crucial task required for the probability, hazard, risk mapping, and mitigation purposes. Earthquake prediction attracts the researchers' attention from both academia and industries. Traditionally, the risk assessment approaches have used various traditional and machine learning models. However, deep learning techniques have been rarely tested for earthquake probability mapping. Therefore, this study develops a convolutional neural network (CNN) model for earthquake probability assessment in NE India. Then conducts vulnerability using analytical hierarchy process (AHP), Venn's intersection theory for hazard, and integrated model for risk mapping. A prediction of classification task was performed in which the model predicts magnitudes more than 4 Mw that considers nine indicators. Prediction classification results and intensity variation were then used for probability and hazard mapping, respectively. Finally, earthquake risk map was produced by multiplying hazard, vulnerability, and coping capacity. The vulnerability was prepared by using six vulnerable factors, and the coping capacity was estimated by using the number of hospitals and associated variables, including budget available for disaster management. The CNN model for a probability distribution is a robust technique that provides good accuracy. Results show that CNN is superior to the other algorithms, which completed the classification prediction task with an accuracy of 0.94, precision of 0.98, recall of 0.85, and F1 score of 0.91. These indicators were used for probability mapping, and the total area of hazard (21,412.94 km2), vulnerability (480.98 km2), and risk (34,586.10 km2) was estimated.
2021, 12(3): 101125.
doi: 10.1016/j.gsf.2020.12.006
Abstract:
The analysis of early stage rodingite from the ultramafic rocks of the Xialu Massif in the Xigaze Ophiolite, Tibet, in China shows that the rodingitization involved continuous changes in fluid composition during different stages of subduction. The early stage prehnite-bearing rodingite was produced at low pressures and temperatures along extensional fractures. Samples of rodingite were collected along a profile from the center to the margin of a rodingitized intrusive igneous rock (~10 m × 30 m), and they record wide variations in bulk composition, mineralogy, and texture. The mineral assemblages, from center to margin, vary from (1) relics of primary clinopyroxene (Cpxr) and primary amphibole (Ampr) + newly formed late amphibole (Act) + primary plagioclase (Plr) + clinozoisite + prehnite + albite + chlorite + titanite + ilmenite (R1 rodingite), through (2) relics of primary clinopyroxene (Cpxr) + newly formed late clinopyroxene (Cpxn) + primary and late amphiboles (Ampr + Act) + clinozoisite + prehnite + albite + chlorite + titanite (R2 rodingite), to (3) newly formed late clinopyroxene (Cpxn) and amphibole (Act) + clinozoisite + prehnite + albite + chlorite + titanite (R3 rodingite). As a result of the metasomatic process of rodingitization, the content of CaO in the whole rock chemical composition from R1 to R3 increases, SiO2 decreases, and Na2O + K2O is almost completely removed. Mass-balance diagrams show enrichments in large ion lithophile elements such as Rb, Cs, Ba, and Pb as well as Ni during rodingitization. The central part of the rodingitized intrusion (R1 rodingite) was only slightly affected by metasomatism. On the other hand, the contents of the rare earth elements (REEs), high field strength elements (HFSEs; e.g. Zr, Nb, Ta, Hf, and Y), and some highly compatible elements such as Cr and Sc decreased slightly during rodingitization. Thermodynamic modeling based on equilibrium mineral assemblages indicates that the rodingite of the Xialu Massif formed in an H2O-saturated, CO2-rich environment. The estimated conditions of metamorphism were ~281-323℃ and 0.4-3.9 kbar, representing the subgreenschist facies. In this environment, REEs and HFSEs were soluble in the fluids and partly removed. Moreover, these prehnite rodingites formed in a progressively reducing and less alkaline environment, as indicated by decreases in f(O2) and bulk-rock Fe3+/Fe2+ ratios, and the records of fluid ΔpH from the center to the margin of the studied rodingitized intrusion.
The analysis of early stage rodingite from the ultramafic rocks of the Xialu Massif in the Xigaze Ophiolite, Tibet, in China shows that the rodingitization involved continuous changes in fluid composition during different stages of subduction. The early stage prehnite-bearing rodingite was produced at low pressures and temperatures along extensional fractures. Samples of rodingite were collected along a profile from the center to the margin of a rodingitized intrusive igneous rock (~10 m × 30 m), and they record wide variations in bulk composition, mineralogy, and texture. The mineral assemblages, from center to margin, vary from (1) relics of primary clinopyroxene (Cpxr) and primary amphibole (Ampr) + newly formed late amphibole (Act) + primary plagioclase (Plr) + clinozoisite + prehnite + albite + chlorite + titanite + ilmenite (R1 rodingite), through (2) relics of primary clinopyroxene (Cpxr) + newly formed late clinopyroxene (Cpxn) + primary and late amphiboles (Ampr + Act) + clinozoisite + prehnite + albite + chlorite + titanite (R2 rodingite), to (3) newly formed late clinopyroxene (Cpxn) and amphibole (Act) + clinozoisite + prehnite + albite + chlorite + titanite (R3 rodingite). As a result of the metasomatic process of rodingitization, the content of CaO in the whole rock chemical composition from R1 to R3 increases, SiO2 decreases, and Na2O + K2O is almost completely removed. Mass-balance diagrams show enrichments in large ion lithophile elements such as Rb, Cs, Ba, and Pb as well as Ni during rodingitization. The central part of the rodingitized intrusion (R1 rodingite) was only slightly affected by metasomatism. On the other hand, the contents of the rare earth elements (REEs), high field strength elements (HFSEs; e.g. Zr, Nb, Ta, Hf, and Y), and some highly compatible elements such as Cr and Sc decreased slightly during rodingitization. Thermodynamic modeling based on equilibrium mineral assemblages indicates that the rodingite of the Xialu Massif formed in an H2O-saturated, CO2-rich environment. The estimated conditions of metamorphism were ~281-323℃ and 0.4-3.9 kbar, representing the subgreenschist facies. In this environment, REEs and HFSEs were soluble in the fluids and partly removed. Moreover, these prehnite rodingites formed in a progressively reducing and less alkaline environment, as indicated by decreases in f(O2) and bulk-rock Fe3+/Fe2+ ratios, and the records of fluid ΔpH from the center to the margin of the studied rodingitized intrusion.
2021, 12(3): 101126.
doi: 10.1016/j.gsf.2020.12.007
Abstract:
The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane (SGT) in India and is mainly composed of charnockitic rocks and felsic gneisses (charnockite suite). In this study, we present petrologic, geochemical, zircon U-Pb, REE, and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block. Based on field investigations and petrologic studies, the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene. The charnockites and leucogneiss show transition from adakites to non-adakitic magmatic rocks, with enrichment in LREEs (light rare earth elements) and LILEs (large ion lithophile elements), and depletion in HREEs (heavy rare earth elements) and HFSEs (high field strength elements). Some of the charnockites and the leucogneiss show typical HSA (high silica adakite) characters, (high SiO2, Al2O3, Ba-Sr, La/Yb, and Sr/Y). The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge. The high Ba-Sr features were possibly inherited from subducted oceanic crust melting under high thermal gradient during Precambrian. The magmas were underplated and subjected to fractional crystallization. Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims. Magmatic zircon grains from the charnockites show ages ranging from 1983 ± 8.8 Ma to 2046 ± 14 Ma, and the metamorphic domains show an age range of 502 ± 14 Ma to 547 ± 8.7 Ma. Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860 ± 20 Ma and 575.6 ± 8.8 Ma. Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma. The REE data of the zircon grains show LREE depletion and HREE enrichment, with the metamorphic grains showing more depletion in HREE. Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yielded εHf(t) values from -1.17 to 0.46 with TDM and TDMC and age peaks at 2392 Ma and 2638 Ma, suggesting Neoarchean to Paleoproterozoic juvenile sources. We suggest that the high Ba-Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent, and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic-Cambrian. Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.
The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane (SGT) in India and is mainly composed of charnockitic rocks and felsic gneisses (charnockite suite). In this study, we present petrologic, geochemical, zircon U-Pb, REE, and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block. Based on field investigations and petrologic studies, the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene. The charnockites and leucogneiss show transition from adakites to non-adakitic magmatic rocks, with enrichment in LREEs (light rare earth elements) and LILEs (large ion lithophile elements), and depletion in HREEs (heavy rare earth elements) and HFSEs (high field strength elements). Some of the charnockites and the leucogneiss show typical HSA (high silica adakite) characters, (high SiO2, Al2O3, Ba-Sr, La/Yb, and Sr/Y). The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge. The high Ba-Sr features were possibly inherited from subducted oceanic crust melting under high thermal gradient during Precambrian. The magmas were underplated and subjected to fractional crystallization. Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims. Magmatic zircon grains from the charnockites show ages ranging from 1983 ± 8.8 Ma to 2046 ± 14 Ma, and the metamorphic domains show an age range of 502 ± 14 Ma to 547 ± 8.7 Ma. Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860 ± 20 Ma and 575.6 ± 8.8 Ma. Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma. The REE data of the zircon grains show LREE depletion and HREE enrichment, with the metamorphic grains showing more depletion in HREE. Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yielded εHf(t) values from -1.17 to 0.46 with TDM and TDMC and age peaks at 2392 Ma and 2638 Ma, suggesting Neoarchean to Paleoproterozoic juvenile sources. We suggest that the high Ba-Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent, and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic-Cambrian. Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.
2021, 12(3): 101128.
doi: 10.1016/j.gsf.2020.12.009
Abstract:
This study investigates the values of pH, total dissolved solids (TDS), elevation, oxidative reduction potential (ORP), temperature, and depth, while the concentrations of Br, and potentially harmful metals (PHMs) such as Cr, Ni, Cd, Mn, Cu, Pb, Co, Zn, and Fe in the groundwater samples. Moreover, geographic information system (GIS), XLSTAT, and IBM SPSS Statistics 20 software were used for spatial distribution modeling, principal component analysis (PCA), cluster analysis (CA), and Quantile-Quantile (Q-Q) plotting to determine groundwater pollution sources, similarity index, and normal distribution reference line for the selected parameters. The mean values of pH, TDS, elevation, ORP, temperature, depth, and Br were 7.2, 322 mg/L, 364 m, 188 mV, 29.6℃, 70 m, 0.20 mg/L, and PHMs like Cr, Ni, Cd, Mn, Cu, Pb, Co, Zn, and Fe were 0.38, 0.26, 0.08, 0.27, 0.36, 0.22, 0.04, 0.43 and 0.86 mg/L, respectively. PHMs including Cr (89%), Cd (43%), Mn (23%), Pb (79%), Co (20%), and Fe (91%) exceeded the guideline values set by the world health organization (WHO). The significant R2 values of PCA for selected parameters were also determined (0.62, 0.67, 0.78, 0.73, 0.60, 0.87, -0.50, 0.69, 0.70, 0.74, -0.50, 0.70, 0.67, 0.79, 0.59, and -0.55, respectively). PCA revealed three geochemical processes such as geogenic, anthropogenic, and reducing conditions. The mineral phases of Cd(OH)2, Fe(OH)3, FeOOH, Mn3O4, Fe2O3, MnOOH, Pb(OH)2, Mn(OH)2, MnO2, and Zn(OH)2 (-3.7, 3.75, 9.7, -5.8, 8.9, -3.6, 2.2, -4.6, -7.7, -0.9, and 0.003, respectively) showed super-saturation and under-saturation conditions. Health risk assessment (HRA) values for PHMs were also calculated and the values of hazard quotient (HQ), and hazard indices (HI) for the entire study area were increased in the following order:Cd > Ni > Cu > Pb > Mn > Zn > Cr. Relatively higher HQ and HI values of Ni, Cd, Pb, and Cu were greater than one showing unsuitability of groundwater for domestic, agriculture, and drinking purposes. The long-term ingestion of groundwater could also cause severe health concerns such as kidney, brain dysfunction, liver, stomach problems, and even cancer.
This study investigates the values of pH, total dissolved solids (TDS), elevation, oxidative reduction potential (ORP), temperature, and depth, while the concentrations of Br, and potentially harmful metals (PHMs) such as Cr, Ni, Cd, Mn, Cu, Pb, Co, Zn, and Fe in the groundwater samples. Moreover, geographic information system (GIS), XLSTAT, and IBM SPSS Statistics 20 software were used for spatial distribution modeling, principal component analysis (PCA), cluster analysis (CA), and Quantile-Quantile (Q-Q) plotting to determine groundwater pollution sources, similarity index, and normal distribution reference line for the selected parameters. The mean values of pH, TDS, elevation, ORP, temperature, depth, and Br were 7.2, 322 mg/L, 364 m, 188 mV, 29.6℃, 70 m, 0.20 mg/L, and PHMs like Cr, Ni, Cd, Mn, Cu, Pb, Co, Zn, and Fe were 0.38, 0.26, 0.08, 0.27, 0.36, 0.22, 0.04, 0.43 and 0.86 mg/L, respectively. PHMs including Cr (89%), Cd (43%), Mn (23%), Pb (79%), Co (20%), and Fe (91%) exceeded the guideline values set by the world health organization (WHO). The significant R2 values of PCA for selected parameters were also determined (0.62, 0.67, 0.78, 0.73, 0.60, 0.87, -0.50, 0.69, 0.70, 0.74, -0.50, 0.70, 0.67, 0.79, 0.59, and -0.55, respectively). PCA revealed three geochemical processes such as geogenic, anthropogenic, and reducing conditions. The mineral phases of Cd(OH)2, Fe(OH)3, FeOOH, Mn3O4, Fe2O3, MnOOH, Pb(OH)2, Mn(OH)2, MnO2, and Zn(OH)2 (-3.7, 3.75, 9.7, -5.8, 8.9, -3.6, 2.2, -4.6, -7.7, -0.9, and 0.003, respectively) showed super-saturation and under-saturation conditions. Health risk assessment (HRA) values for PHMs were also calculated and the values of hazard quotient (HQ), and hazard indices (HI) for the entire study area were increased in the following order:Cd > Ni > Cu > Pb > Mn > Zn > Cr. Relatively higher HQ and HI values of Ni, Cd, Pb, and Cu were greater than one showing unsuitability of groundwater for domestic, agriculture, and drinking purposes. The long-term ingestion of groundwater could also cause severe health concerns such as kidney, brain dysfunction, liver, stomach problems, and even cancer.
2021, 12(3): 101123.
doi: 10.1016/j.gsf.2020.11.017
Abstract:
This study presents new major, trace and REE data for thirty-five ferromanganese nodules recovered from areas representing three different sediment types (siliceous, red clay and their transition zone) in the Central Indian Ocean Basin (CIOB) to address their genetic aspects, classification, growth rate, nature of host sediments and influence of REE in the processes of nodule formation. The nodules from CIOB are mostly either hydrogenetic (metals coming from oxygenated bottom water) and diagenetic (metals coming from suboxic sediment pore water) or a combination of both, depending on the source of supply of metal. However, a number of biogeochemical processes mediate this supply of metals which again changes from time to time, making the nodule growth process highly dynamic. This study suggests that at the initial stage of nodule growth, host sediments do not play much role in controlling the growth processes for which REEs can enter both Mn and Fe oxyhydroxide phases equally. Thus, the bottom water signature is imprinted in these early formed nodules irrespective of their host sediment substrate but with gradual growth and burial in the sediment, the main mode of metal enrichment becomes diagenetic through sediment pore water. This tends to increase the concentration of Mn, Ni and Cu over other elements which are retained in the sediment fraction. Among the REEs, Ce concentration of the nodules shows significant positive anomaly due to variation in redox potential and hence its magnitude can be used to get an idea about the metal enrichment procedure and the genetic type of the nodules. However, based on host sediment only, not much difference is found in the magnitude of Ce anomaly in these nodules. On the other hand, discrimination diagram, based on HFSE and REY chemistry, indicates that most of these nodules are of diagenetic origin under oxic condition with a trend towards hydrogenetic field. Further, the genetic type of the ferromanganese nodules from the CIOB are more effectively differentiated by a combination of their major and trace element concentrations rather than solely based on their REE or HFSE chemistry or host sediment substrate.
This study presents new major, trace and REE data for thirty-five ferromanganese nodules recovered from areas representing three different sediment types (siliceous, red clay and their transition zone) in the Central Indian Ocean Basin (CIOB) to address their genetic aspects, classification, growth rate, nature of host sediments and influence of REE in the processes of nodule formation. The nodules from CIOB are mostly either hydrogenetic (metals coming from oxygenated bottom water) and diagenetic (metals coming from suboxic sediment pore water) or a combination of both, depending on the source of supply of metal. However, a number of biogeochemical processes mediate this supply of metals which again changes from time to time, making the nodule growth process highly dynamic. This study suggests that at the initial stage of nodule growth, host sediments do not play much role in controlling the growth processes for which REEs can enter both Mn and Fe oxyhydroxide phases equally. Thus, the bottom water signature is imprinted in these early formed nodules irrespective of their host sediment substrate but with gradual growth and burial in the sediment, the main mode of metal enrichment becomes diagenetic through sediment pore water. This tends to increase the concentration of Mn, Ni and Cu over other elements which are retained in the sediment fraction. Among the REEs, Ce concentration of the nodules shows significant positive anomaly due to variation in redox potential and hence its magnitude can be used to get an idea about the metal enrichment procedure and the genetic type of the nodules. However, based on host sediment only, not much difference is found in the magnitude of Ce anomaly in these nodules. On the other hand, discrimination diagram, based on HFSE and REY chemistry, indicates that most of these nodules are of diagenetic origin under oxic condition with a trend towards hydrogenetic field. Further, the genetic type of the ferromanganese nodules from the CIOB are more effectively differentiated by a combination of their major and trace element concentrations rather than solely based on their REE or HFSE chemistry or host sediment substrate.
2021, 12(3): 101129.
doi: 10.1016/j.gsf.2020.12.010
Abstract:
Having a better understanding of air pollutants in railway systems is crucial to ensure a clean public transport. This study measured, for the first time in Brazil, nanoparticles (NPs) and black carbon (BC) on two ground-level platforms and inside trains of the Metropolitan Area of Porto Alegre (MAPA). An intense sampling campaign during thirteen consecutive months was carried out and the chemical composition of NPs was examined by advanced microscopy techniques. The results showed that highest concentrations of the pollutants occur in colder seasons and influenced by variables such as frequency of the trains and passenger densities. Also, internal and external sources of pollution at the stations were identified. The predominance of NPs enriched with metals that increase oxidative stress like Cd, Fe, Pb, Cr, Zn, Ni, V, Hg, Sn, and Ba both on the platforms and inside trains, including Fe-minerals as hematite and magnetite, represents a critical risk to the health of passengers and employees of the system. This interdisciplinary and multi-analytical study aims to provide an improved understanding of reported adverse health effects induced by railway system aerosols.
Having a better understanding of air pollutants in railway systems is crucial to ensure a clean public transport. This study measured, for the first time in Brazil, nanoparticles (NPs) and black carbon (BC) on two ground-level platforms and inside trains of the Metropolitan Area of Porto Alegre (MAPA). An intense sampling campaign during thirteen consecutive months was carried out and the chemical composition of NPs was examined by advanced microscopy techniques. The results showed that highest concentrations of the pollutants occur in colder seasons and influenced by variables such as frequency of the trains and passenger densities. Also, internal and external sources of pollution at the stations were identified. The predominance of NPs enriched with metals that increase oxidative stress like Cd, Fe, Pb, Cr, Zn, Ni, V, Hg, Sn, and Ba both on the platforms and inside trains, including Fe-minerals as hematite and magnetite, represents a critical risk to the health of passengers and employees of the system. This interdisciplinary and multi-analytical study aims to provide an improved understanding of reported adverse health effects induced by railway system aerosols.
2021, 12(3): 101124.
doi: 10.1016/j.gsf.2020.12.005
Abstract:
Continental crust in average exhibits a similar composition in both major and trace elements to andesites along active continental margins. For this reason, andesitic magmatism above oceanic subduction zones is considered to have played a key role in the generation of continental crust along convergent plate boundaries. With respect to the origin of andesites themselves, however, there is still a hot debate on how they have acquired their geochemcial compositions. The debate is mainly centralized on the relative contributions of crustal contamination, magma differentiation and source mixing, which reaches an impasse in the past decades. The essential reason for this kind of debates is that these three mechanisms only can account for some of the geochemical observations for andesites, leading to insufficient discrimination among them. Nevertheless, the geochemical features of andesites are primarily controled from early to late by the composition of their source rocks in addition to partial melting and magma differentiation processes. If source mixing and partial melting processes in the early stage of andesite magmatism can account for the first-order geochemical features of andesites, there is no need to invoke the late processes of magma differentiation and crustal contamination for andesite petrogenesis. This is illustrated by quantitative forward modeling of the geochemical data for Quaternary andesites from the Andean arc in South America based on an integrated interpretation of these data. The modeling has run with four steps from early to late:(1) dehydration of the subducting oceanic crust at forearc depths; (2) partial melting of the subducting terrigenous sediment and altered oceanic basalt at subarc depths to produce hydrous felsic melts; (3) the generation of basaltic metasomatites (e.g., Si-excess pyroxenite) in the mantle wedge through reaction of the mantle wedge peridotite with large amounts of the hydrous felsic melts; (4) the production of andesitic melts by partial melting of the basaltic metasomatites. The results not only testify the hypothesis that the trace element and radiogenic isotope compositions of andesites can be directly produced by the source mixing and mantle melting but also demonstrate that partial melting of the basaltic metasomatites can reproduce the lithochemical composition of andesites. The compositional variations of Andean andesites within a single volcanic zone and among different volcanic zones can be explained by incorporating different amounts of heterogeneous hydrous felsic melts into their mantle sources, followed by different degree of partial melting under different pressures and temperatures. Therefore, the source mixing and partial melting processes at subarc depths can account for the first-order geochemical features of Andean andesites. In this regard, it may be not necessary for andesite petrogenesis to invoke the significant contributions from the processes of magma differentiation and crustal contamination.
Continental crust in average exhibits a similar composition in both major and trace elements to andesites along active continental margins. For this reason, andesitic magmatism above oceanic subduction zones is considered to have played a key role in the generation of continental crust along convergent plate boundaries. With respect to the origin of andesites themselves, however, there is still a hot debate on how they have acquired their geochemcial compositions. The debate is mainly centralized on the relative contributions of crustal contamination, magma differentiation and source mixing, which reaches an impasse in the past decades. The essential reason for this kind of debates is that these three mechanisms only can account for some of the geochemical observations for andesites, leading to insufficient discrimination among them. Nevertheless, the geochemical features of andesites are primarily controled from early to late by the composition of their source rocks in addition to partial melting and magma differentiation processes. If source mixing and partial melting processes in the early stage of andesite magmatism can account for the first-order geochemical features of andesites, there is no need to invoke the late processes of magma differentiation and crustal contamination for andesite petrogenesis. This is illustrated by quantitative forward modeling of the geochemical data for Quaternary andesites from the Andean arc in South America based on an integrated interpretation of these data. The modeling has run with four steps from early to late:(1) dehydration of the subducting oceanic crust at forearc depths; (2) partial melting of the subducting terrigenous sediment and altered oceanic basalt at subarc depths to produce hydrous felsic melts; (3) the generation of basaltic metasomatites (e.g., Si-excess pyroxenite) in the mantle wedge through reaction of the mantle wedge peridotite with large amounts of the hydrous felsic melts; (4) the production of andesitic melts by partial melting of the basaltic metasomatites. The results not only testify the hypothesis that the trace element and radiogenic isotope compositions of andesites can be directly produced by the source mixing and mantle melting but also demonstrate that partial melting of the basaltic metasomatites can reproduce the lithochemical composition of andesites. The compositional variations of Andean andesites within a single volcanic zone and among different volcanic zones can be explained by incorporating different amounts of heterogeneous hydrous felsic melts into their mantle sources, followed by different degree of partial melting under different pressures and temperatures. Therefore, the source mixing and partial melting processes at subarc depths can account for the first-order geochemical features of Andean andesites. In this regard, it may be not necessary for andesite petrogenesis to invoke the significant contributions from the processes of magma differentiation and crustal contamination.
2021, 12(3): 101111.
doi: 10.1016/j.gsf.2020.11.008
Abstract:
Detailed interpretation of seismic stratigraphic sequences in the Laxmi Basin of the eastern Arabian Sea are presented in this study using closely spaced high resolution multi-channel seismic (MCS) data. Our stratigraphic interpretation is further corroborated using recent drilling results in the Laxmi Basin, derived from the long sediment cores collected during International Ocean Discovery Program (IODP) Expedition 355. Integrated core-log interpretation discussed in the present study, offer important insights about the lithostratigraphic variations in this region. Analyses of multi-channel seismic reflection data reveal five depositional sequences (ranging from Paleocene to Recent) that led to the development of this marginal basin since the Cenozoic period. Regional igneous basement is successfully imaged, which was also validated by deep sea coring during the IODP Expedition 355. In the present study, we primarily focus on the post-rift sedimentation in the Laxmi Basin and its possible mechanisms. Our detailed interpretation in the prevailing tectonic framework of the basin suggests that near-shelf oldest volcaniclastic sedimentation immediately overlying the acoustic basement is linked to the onset of India-Madagascar and India-Seychelles rifting activities during the Late Cretaceous period. Eventually, during the Early-Mid to Late Miocene, the basin received maximum sedimentation dominantly through an extensive mass transport mechanism implying possible large-scale deformation on the Indian shelf. Subsequent sediment input to the basin appears to have been fed variably via the Indus Fan as well as coastal discharge from the Indian mainland. The total sediment thickness in the Laxmi Basin ranges from 1.1 to 3.5 km. New stratigraphic information and sediment isopach maps presented here provide vital information about syn- and post-rift sedimentation pattern in the region and their long term tectonic implications.
Detailed interpretation of seismic stratigraphic sequences in the Laxmi Basin of the eastern Arabian Sea are presented in this study using closely spaced high resolution multi-channel seismic (MCS) data. Our stratigraphic interpretation is further corroborated using recent drilling results in the Laxmi Basin, derived from the long sediment cores collected during International Ocean Discovery Program (IODP) Expedition 355. Integrated core-log interpretation discussed in the present study, offer important insights about the lithostratigraphic variations in this region. Analyses of multi-channel seismic reflection data reveal five depositional sequences (ranging from Paleocene to Recent) that led to the development of this marginal basin since the Cenozoic period. Regional igneous basement is successfully imaged, which was also validated by deep sea coring during the IODP Expedition 355. In the present study, we primarily focus on the post-rift sedimentation in the Laxmi Basin and its possible mechanisms. Our detailed interpretation in the prevailing tectonic framework of the basin suggests that near-shelf oldest volcaniclastic sedimentation immediately overlying the acoustic basement is linked to the onset of India-Madagascar and India-Seychelles rifting activities during the Late Cretaceous period. Eventually, during the Early-Mid to Late Miocene, the basin received maximum sedimentation dominantly through an extensive mass transport mechanism implying possible large-scale deformation on the Indian shelf. Subsequent sediment input to the basin appears to have been fed variably via the Indus Fan as well as coastal discharge from the Indian mainland. The total sediment thickness in the Laxmi Basin ranges from 1.1 to 3.5 km. New stratigraphic information and sediment isopach maps presented here provide vital information about syn- and post-rift sedimentation pattern in the region and their long term tectonic implications.
