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

摘要

New sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages, geochemical data, and a synthesis of existing stratigraphic, geochronologic, and geochemical 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-ultramafic 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.