Composition of plagioclase in Dabie Early Cretaceous granitoids:influence of fractional crystallization on whole-rock Sr–Ca O correlations  

作　　者：Hongjie Wu Yongsheng He Zhenhui Hou Shuguang Li 

机构地区：[1]State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences [2]School of Earth and Space Sciences, CAS Key Laboratory of Crust-Mantle Materials and Environments, University of Science and Technology of China

出　　处：《Chinese Science Bulletin》2014年第34期4809-4815,共7页

基　　金：supported by theFundamental Research Funds for the Central Universities(2-9-2012-129)

摘　　要：Identifying melts of thickened lower continental crust from high Sr/Y rocks is very important to trace deep crustal processes. Recent studies on Dabie Early Cretaceous granitoids have revealed that melts derived from thickened lower continental crust have higher Sr/Ca O ratios and define a high Sr evolution trend compared with normal granitoids. Fractional crystallization of plagioclase can significantly change Sr and Ca O contents of melts, but its role in controlling the Sr/Ca O ratios of the melts is still unclear. This study gives a direct comparison of plagioclase compositions between normal granitoids and low-Mg adakitic rocks. On the basis of Sr–Ca exchange partition coefficient, discussions on effect of plagioclase crystallization on Sr/Ca O ratios of melts show that fractional crystallization of abundant plagioclase cannot significantly change Sr/Ca O ratios of granitic melts, which are inherited from their individual initial melts. High Sr/Ca O ratios indicate the absence of plagioclase in sources of granitic melts. Therefore, high Sr/Ca O correlation can be an important indicator to identify melts derived from thickened lower continental crust.Identifying melts of thickened lower continental crust from high Sr/Y rocks is very important to trace deep crustal processes. Recent studies on Dabie Early Cretaceous granitoids have revealed that melts derived from thickened lower continental crust have higher Sr/CaO ratios and define a high Sr evolution trend compared with normal granitoids. Fractional crystallization of plagioclase can significantly change Sr and CaO contents of melts, but its role in controlling the Sr/CaO ratios of the melts is still unclear. This study gives a direct comparison of plagioclase compositions between normal granitoids and low-Mg adakitic rocks. On the basis of Sr-Ca exchange partition coefficient, discussions on effect of plagioclase crystallization on Sr/CaO ratios of melts show that fractional crystallization of abundant plagioclase cannot significantly change Sr/CaO ratios of granitic melts, which are inherited from their individual initial melts. High Sr/CaO ratios indicate the absence of plagioclase in sources of granitic melts. Therefore, high Sr/CaO correlation can be an important indicator to identify melts derived from thickened lower continental crust.

关 键 词：锶/钙比值 斜长花岗岩 分步结晶 早白垩世 斜长石 大别山 组成 下地壳熔融 

分 类 号：P588.121[天文地球—岩石学]