Geochronology, Geochemistry and Petrogenesis of Diabase Dyke Swarms in East Tianshan, Xinjiang, NW China

Abstract:Diabase dyke swarms are widespread in the East Tianshan and Beishan regions. LA‐ICP‐MS zircon U‐Pb ages of these diabase vary from 305 Ma to 278 Ma, showing that these dykes were formed during Late Carboniferous‐Early Permian magmatism. All diabase samples are subalkali calc‐alkali, characterized by slight LREE and LILEs enrichment, and weak negative Ti, Nb and Ta anomalies. The diabase samples have positive εNd(t) values (>+3), high Sr isotopic compositions (initial 87Sr/86Sr values=0.7030–0.7097), and large variation of Pb isotopic compositions, indicating they were derived from a deplete mantle source. Regional geology and geochemistry evidences indicate that these diabase dyke swarms were generated in a lithosphere extensional setting and had the same magma sources. Initial magmas may be a mixture of depleted asthenosphere mantle and enriched lithospheric mantle during rapid magma ascending.