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A Permian large igneous province in Tarim and Central Asian orogenic belt, NW China,Results of a ca.275 Ma mantle plume [查看] Chuan-LinZhang、Zheng-XiangLi、Xian-HuaLi、Yi-GangXu、GangZhou、Hai-MinYe

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 Per mian (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 fl air 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.

Early history of the eastern Sibao Orogen (South China) during the assembly of Rodinia New mica 40Ar39Ar dating andSHRIMP U–Pb detrital zircon provenance constraints [查看] Zheng-XiangLi、Jo-AnneWartho、SandraOcchipinti、Chuan-LinZhang、Xian-HuaLi、JianWang、ChaominBao

The Sibao Orogen in South China is one of the poorest known Grenville-aged orogenic belts through which the Neoproterozoic supercontinent Rodinia assembled. We report here the first UV laser spot 40Ar/39Ar mica and SHRIMP U–Pb zircon ages from a rare Grenville-aged metamorphic complex, the Tianli Schists, in the eastern Sibao Orogen. Our U–Pb zircon provenance ages indicate that the protolith of the Tianli Schists was a clastic sedimentary succession most likely derived from the Yangtze Block.The depositional age of the protolith is younger than 1530 Ma, as constrained by the youngest detrital zircon grains, but is older than 1040 Ma as constrained by the oldest 40Ar/39Ar muscovite ages. The Yangtze Block provenance for the Tianli Schists suggests that the Sibaoan ophiolitic complexes in northeastern Jiangxi, the ca. 970 Ma Xiwan adakitic granite intrusions, and the ca. 900 Ma(?) Xiwan blueschists, all to the northwest of the study region, were likely formed during the closure of a back-arc basin along the margin of the Yangtze Block. Our in situ UV laser 40Ar/39Ar results from S1 and S2 muscovites suggest that the Tianli Schists underwent metamorphism and deformation at 1042±7Ma to 1015±4 Ma, the oldest known metamorphic event in the easternSibao Orogen. Muscovite/biotite cooling ages of ca. 968±4 and 942±8Ma are recorded by deformed and recrystallised muscovite and biotite, respectively, indicating tectonic reactivation before 900 Ma, during the later stages of the Sibao Orogeny. Together with previous results from the western Sibao Orogen, our work suggests that the closure of the ocean between the Yangtze and Cathaysia Blocks during the assembly of Rodinia was diachronous: ≥1000 Ma at the western Sibao Orogen and ca. 900 Ma at the eastern Sibao Orogen.

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