
Uranium series disequilibrium constraints on the formation and evolution of granite regolith in Longnan, Jiangxi Province
Guodong JIA, Sheng XU, Congqiang LIU
Uranium series disequilibrium constraints on the formation and evolution of granite regolith in Longnan, Jiangxi Province
The granitic regolith, prevalent across South China, plays a pivotal role in geomorphological evolution, ecological dynamics, and mineral resource management. Understanding the formation and evolution of regolith hinges upon fundamental parameters such as production rate. The U-series disequilibrium method serves as a crucial geochemical tool for determining regolith production rates, yet its application in China has been limited due to the unavailability of a spike. In this investigation, the U-series disequilibrium method was employed to ascertain the production rate of granitic regolith in Longnan, Jiangxi Province. Results indicate U and Th contents in the regolith profile ranging from (3.25-3.39)×10-6 and (41.46-47.67)×10-6, respectively. Activity ratios of (234U/238U)a, (230Th/234U)a, and (230Th/232Th)a vary between 1.008-1.023, 1.063-1.112, and 0.239-0.271, respectively. Consequently, utilizing the U-series disequilibrium method to fit uranium isotopes, the evolution time of the regolith within the 20-120 cm stratum is estimated at ~841 ka, with a regolith production rate determined to be ~1.2 m/Ma. Surface cover emerges as the predominant control factor over regolith production rate, with minimal influence from climate and tectonic activity. Furthermore, the regolith’s evolution state is identified as non-steady state, evidenced by a significantly lower regolith production rate compared to denudation rates determined by cosmogenic nuclides, resulting in gradual thickness reduction.
U-series disequilibrium / production rate / granitic regolith / evolution state / non-steady state
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