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

Abstract

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.

Geochemical Distribution of Some Heavy Metals in Agricultural Soil and Their Environmental Impacts in Kirkuk, Northern Iraq

“…It was also observed that the Sr correlated with a positive and strong significant relationship with CaO (r = 0.87, r = 0.85; n=15), CaCO3 (r = 0.71, r = 0.55; n=15) and a positive relationship with SO3 and CaSO4.2H2O in the surface and subsurface horizon of the soil respectively, which indicates the enrichment of limestone rocks with the Sr compared to silicate rocks, as they spread within a region The study detects limestone to form the hatch. This may be attributed to their co-occurrence in the mineral plagioclase (Wu et al, 2014). Calcium and strontium originate mainly from limestone, and differences in the concentration of trace elements in the fine fractions depend on the presence of CaSO4•2H2O (Pavlin et al, 2018).…”