Geological cycling of potassium and the K isotopic response:insights from loess and shales

查看全文 作　　者：Weiqiang [1]Li;Shilei [2]Li;Brian [3,4]L.Beard

机构地区：[1]State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210046,People's Republic of China;[2]MOE Key Laboratory of Surficial Geochemistry,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210046,People's Republic of China;[3]Department of Geoscience,University of Wisconsin- Madison,1215W Dayton Street,Madison,WI 53706,USA;[4]NASA Astrobiology Institute,University of Wisconsin- Madison,Madison,WI 53706,USA

出　　处：《Acta Geochimica》索引2019年第38卷第4期,共9页

基　　金：supported by the National Key R&D Program of China (Project No. 2017YFC0602801);National Science Foundation of China (Grant Nos. 41622301, 41873004);supported by the NASA Astrobiology Institute (NNA13AA94A to BLB);the National Science Foundation (1741048-EAR to BLB) 摘　　要：Shales are a major sink for K into seawater delivered from continental weathering,and are potential recorders of K cycling.High precision K isotope analyses reveal a[0.6%variation in δ^41K values(41K/39K relative to NIST SRM 3141a)from a set of well characterized postArchean Australian shale(PAAS)samples.By contrast,loess samples have relatively homogenous δ^41K values(-0.5±0.1%),which may represent the average K composition of upper continental crust.Most of the shales analyzed in this study have experienced K enrichment relative to average continental crust,and the majority of them define a trend of decreasing δ^41K value(from-0.5to-0.7%)with increasing K content and K/Na ratio,indicating cation exchange in clays minerals is accompanied by K isotope fractionation.Several shale samples do not follow the trend and have elevated δ^41K values up to-0.1%,and these samples are characterized by variable Fe isotope compositions,which reflect post-depositional processes.The K isotope variability observed in shales,in combination with recent findings about K isotope fractionation during continental weathering,indicates that K isotopes fractionate during cycling of K between different reservoirs,and K isotopes in sediments may be used to trace geological cycling of K. 关键词：K ISOTOPES LOESS SHALE K cycle

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Geological cycling of potassium and the K isotopic response:insights from loess and shales

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