Chemical weathering of a soil chronosequence on granitoid alluvium : II. Mineralogic and isotopic constraints on the behavior of strontium

摘要: The use of strontium isotopes to evaluate mineral weathering and identify sources base cations in catchment waters requires an understanding the behavior Sr soil environment as a function time. Our approach is model temporal evolution 87Sr/86Sr cation exchange pool chronosequence developed on alluvium derived from central Sierra Nevada granitoids during past 3 Ma. With increasing age, ammonium-acetate extractable initially decreases values typical K-feldspar those plagioclase hornblende then remains constant, even though are absent soils after approximately 1 Ma weathering. variation exchangeable modeled by progressively equilibrating atmospheric deposition with sites infiltrate column. Observed quartz-normalized modal abundances plagioclase, hornblende, time, distinct87Sr/86Sr these minerals can be used calculate flux reactions. Hydrobiotites have nearly constant abundances, chemistry, over provide negligible input solutions. time horizon-dependent changes amount efficiency exchange, well biologic cycling term. predicts that has identical K-feldspar, thus could dominated leached following alluvium. maximum value observed dilute stream associated Yosemite region likewise similar K-feldspars, suggesting not biotite may dominant source radiogenic streams. This study reveals that, when attempting Strontium biomass, both preferential leaching incipient development changing must considered along chemical contributions due dissolution.