Abstract

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Author(s):: ZHU Xiang-kun; SUN Jian; WANG Yue; MLR Key Laboratory of Isotope Geology, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

Keywords:: geochemistry; Fe isotope; magmatic process; partial melting; crystallization process; fluid exsolution; oxygen fugacity; igneous rock

Abstract:: Fe isotopes fractionate during magmatic processes. Comparing to mantle xenoliths (with δ⁵⁶Fe average value of ca. 0‰), basalts incorporate heavier Fe isotopes (with δ⁵⁶Fe average value of 0.1‰). Relative to basic and intermediate magmatite, acidic magmatites show heavy Fe isotope enrichments. The Fe isotope fractionation during magmatic processes is controlled mainly by the oxidation states. Normally, Fe³⁺-bearing minerals (e.g., magmatite) incorporate heavy Fe isotopes than Fe²⁺-bearing minerals (e.g., olivine, pyroxene). During partial melting process, Fe³⁺ is enriched in the melt preferentially, leading to heavy Fe isotopes enriched into the melt. As a result, the partial melting product (normally basalt) incorporates heavy Fe isotopes relate to the residue. During magmatic differentiation, the crystallization of Fe²⁺-bearing minerals such as olivine and pyroxene in low oxygen fugacity condition leads to enrichment of Fe³⁺ thus heavy Fe isotopes in the residual melt; the crystallization of Fe³⁺-bearing minerals such as magnetite in high oxygen fugacity results in enrichment of Fe²⁺ thus light Fe isotopes in residual melt. During fluid exsolution, the exsolved fluid preferentially incorporates light Fe isotopes. It shows that Fe isotope is a powerful tracer for studying magmatic processes.