Potassium isotope characteristics of typical salt lake in key tectonic zones, China: Sources and evolutionary models

Potassium isotopic compositions (δ⁴¹K) have emerged as sensitive tracers in modern environmental processes. Lakkor Co Salt Lake, situated within a critical tectonic zone of the Qinghai-Tibet Plateau (the Bangong-Nujiang tectonic belt), stands as a leading example of applying stable potassium isotopes to decipher diverse geochemical cycles in tectonically active regions. The results demonstrated that the potassium concentration in Lakkor Co can reach up to 2901 mg/L. A distinct potassium isotope fractionation is observed across the system. The δ⁴¹K values vary from -0.82‰ to -0.05‰ in recharge rivers, which are lower than the global riverine range reported in previous studies (-0.59‰ to -0.08‰). In contrast, the surface brine of Lakkor Co exhibits δ⁴¹K values between -0.30‰ and + 0.05‰, falling within the ranges of both modern seawater (-0.01‰ to + 0.14‰) and chloride-dominated brines in the Qaidam Basin (-0.57‰ to + 0.22‰). In combination with hydrochemical, δ¹¹B and δ⁷Li data, the potassium in the Lakkor Co area is sourced from surface rock weathering and geothermal fluid. Moreover, weathering of ultra-high pressure metamorphic zones formed by deep subduction of oceanic crust may represent an additional source, which is supported by the anomalously low δ⁴¹K values observed in the lake basin. This study investigates the sources, geochemical behavior and evolution process of potassium in the Lakkor Co Salt Lake; provide a theoretical basis for subsequent exploration and development of analogous salt lakes; and explore the elemental behavior of subducting oceanic crust.