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

• DOI: 10.1007/s11434-014-0623-9
• Publication Date: 2014-09-23T23:28:56Z
• Authors: Hongjie Wu; Yongsheng He; Zhenhui Hou; Shuguang Li
• Keywords: Fractional crystallization (geology)

Identifying melts of thickened lower continen- tal 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 plagio- clase compositions between normal granitoids and low-Mg adakitic rocks. On the basis of Sr-Ca exchange partition coefficient, discussions on effect of plagioclase crystalli- zation 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 thick- ened lower continental crust.