The Petrology, Geochemistry And Petrogenesis Of The Mesozoic Granites In Erenhot-Xianghuangqi

Study area located at the middle of Xing’an Mongolian orogenic belt, developingsome granites in Mesozoic. Erennaoer pluton, Hemu pluton, Madulatu Graniteporphyry and Weijing pluton are studied in this essay. The detailed outcropinvestigation and lab analysis show that the lithology of granites in Mesozoic areadamellite, moyite and granite porphyry. The LA-ICP-MS data has shown that the agein Hemu pluton is228.9±3.4Ma and it in Weijing pluton is144.7Ma. Erennaoerpluton’s weighted mean age is231.8Ma and Madulatu Granite porphyry’s is151.0±5.0Ma. By the analyses on core and analysis for trace elements, Erennaoerpluton’s lithology is adamellite, Hemu and Weijing plutons’ are moyite, and the plutondeveloped in Jurassic is granite porphyry. Except of Madulatu Granite porphyry,Erennaoer pluton, Hemu pluton and Weijing pluton show the characteristics of A-typegranite. From their Sr-Nd-Pb-Hf isotopes, the provenance of Erennaoer pluton,Madulatu Granite porphyry and Weijing pluton mainly are from depleted mantle,while the provenance of Hemu pluton comes from depleted mantle and crust. Bygeochemical analysis, Erennaoer pluton which formed in early Triassic is A2-typegranite, meaning the end of the orogeny. It indicates that study area was in a changinggeotectonic environment at that time. Hemu pluton is A1-type granite, which formedin Late Triassic. A1-type granite is a sign of the continental rift environment.Madulatu Granite porphyry formed by the mantle-derived magmas in the apotectonicextensional environment. And Weijing pluton formed by the the subduction of thePacific slab and the compression of eurasian continent. Overall, the environment ofstudy area changed from collision to post-collision extensional rifting environment inearly Mesozoic, and then kept this kind of tectonic regime in subsequent period.