A Permian large igneous province in Tarim and Central Asian otogenic, belt, NW China: Results of a ca. 275 Ma mantle plume?

摘要

New sensitive high-resolution ion micro-probe (SHRIMP) U-Pb zircon ages, geo-chemical data, and a synthesis of existing stratigraphic, geochronologic, and geochemi-cal results from the Tarim block and the Central Asian orogenic belt in northwestern China suggest the presence of a Permian (ca. 275 Ma) large igneous province (the Bachu large igneous province). The large igneous province consists predominantly of coeval mafic rocks (basalts and mafic-ultramanc intrusions) having an aerial coverage of more than 600,000 km2, and its formation was accompanied by voluminous emplacement of A-type granites. This large igneous province, interpreted to be of mantle plume origin, is ～15 m.y. older than the ca. 260 Ma Emeishan large igneous province in southwestern China and ～25 m.y. older than the 251 Ma Siberian Trap in Russia. Such a sudden flair up of plume activity in the Permian may represent the early stage of the Pangean superplume event. The Permian plumes likely played a role in late Paleozoic rapid continental crustal growth in the Central Asian orogenic belt In addition, there appear to be two types of mantle geochemical provinces (domains) in the region, a long-term enriched Tarim province and a subduction-metasomatized and depleted Central Asian orogenic belt province.