Indication of Sr Isotopes on Weathering Process of Carbonate Rocks in Karst Area of Southwest China

Abstract

Based on the determination of the major and trace element content, and the Sr isotope composition of soils from limestone and dolomite profiles in the karst area of Southwest (SW) China, this study discussed the distribution and migration characteristics of the elements and the influencing factors of Sr isotope fractionation, in order to better understand the chemical weathering and pedogenesis process, as well as to explore the material source of laterite. The chemical weathering analysis results (Chemical Index of Alteration, mass balance coefficient, and A-CN-K ternary) indicate that the weathering intensity of dolomite profile PB is higher than that of limestone profiles CZ and CY. The correlation analysis between Sr isotopes and P2O5 suggests that in addition to illite, apatite in the dolomite profile also affects the 87Sr/86Sr composition. Sr content and 87Sr/86Sr demonstrate two stages in the weathering process of the carbonate, carbonate dissolution stage, and residual silicate weathering stage. As the carbonate minerals dissolve at the beginning of weathering, the Sr content decreases and 87Sr/86Sr increases slightly. After the decomposition of carbonate, the Sr content remains unchanged and 87Sr/86Sr increases. Finally, the study suggests that the material source of laterite is more likely to be underlying bedrock rather than the aeolian source.