Late Mesozoic topographic evolution of western Transbaikalia: Evidence for
rapid geodynamic changes from the Mongol–Okhotsk collision to
widespread rifting
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Abstract
The Mesozoic geodynamic evolution of Transbaikalia has been largely controlled by the scissors-like closure of the
Mongol–Okhotsk Ocean that separated Siberia from Mongolia–North China continents. Following the oceanic
closure, the tectonic evolution of that region was characterized by collisional uplift and subsequent extension that
gave rise to the formation of metamorphic core complexes. This complex tectonic setting prevailed simultaneously
between 150 Ma and 110 Ma both in Transbaikalia, North Mongolia, and within the North China Craton. Published
paleobotanical and paleontological data show that the oldest Mesozoic basins had formed in western
Transbaikalia before the estimated age of extension onset. However no precise geochronological age is available
for the onset of extension in Transbaikalia. The Tugnuy Basin, as probably the oldest Mesozoic basin in western
Transbaikalia, is a key object to date the onset of extension and following changes in tectonic setting. In this study,
U–Pb (LA-ICP-MS) dating of detrital zircons from three key Jurassic sediment formations of the Tugnuy Basin are
used to identify the potential source areas of the sediments, understand the changes in sediment routing and
provide insights on the topographic evolution of western Transbaikalia. Our results show several significant
changes in tectonic regime after the closure of the Mongol–Okhotsk Ocean. A wide uplifted plateau formed during
the closure of the Mongol–Okhotsk Ocean, determining the Early Jurassic drainage system reaching the Angara-
Vitim batholith to the north and shedding sediments to the continental margin to the South. The following
collisional event at the end of the Early Jurassic led to the uplift of the collision zone, which partially inverted the
drainage system toward the North. A strike-slip displacement induced by the oblique collision initiated some of
the early Transbaikalian depressions, such as the Tugnuy Basin at about 168 Ma. A phase of basin inversion,
marked by folding and erosion of the Upper Jurassic sediments, could correspond to the short-term collision event
that took place during the latest Jurassic–earliest Cretaceous in the eastern Central Asian Orogenic Belt. The
following inversion in tectonic regime from compression to extension is consistent with the mid–lower-crustal
extension that led to the formation of the numerous metamorphic core complexes throughout northeastern
continental Asia during the Early Cretaceous.
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