Geochemistry and Nd-Sr-Pb isotopic compositions of granitoids from qaidam and oulongbuluke micro-blocks, NW China: Constraints on basement nature and tectonic affinity

The formation of major-and trace-elemental and Sr-Nd-Pb isotopic geochemistries in Early Paleoproterozoic Mohe pluton and Early Triassic Cahanno pluton of the Oulongbuluke micro-block and Neoproterozoic Shaliuhe pluton, Late-Permian to Early-Triaasic Xiangride pluton and Late-Triassic Keri pluton of the Qaidam Block of northwestern China, were investigated. The Shaliuhe pluton and Keri muscovite pluton are characterized by S-type and paraaluminium granite, the others are by Ⅰ-type granodiorite or granite. It is concluded from the comparsion of T_ DM and e_ Nd (t) that the magma source area of the Shaliuhe granite belongs to the Ⅱ-type metabasement of the Oulongbuluke micro-block, and the magma of the rest of the plutons could not originate from the exposed supracurstal sequences. The T_ DM are clustered at ~1.5-2.3Ga and 0.9-1.3Ga , with peak value of ~1.2Ga, ~1.6Ga and ~2.05Ga for both granitoids and meta-supracurstal rocks, ~2.5Ga and ~2.8Ga are solely distributed in the Oulongbuluke micro-block. The two micro-blocks have ratios of (~ 206 Pb/~ 204 Pb)_t, (~ 207 Pb/ ~ 204 Pb)_t and (~ 206 Pb/~ 204 Pb)_t generally higher than 18, 15.5 and 38, respectively. These data suggest that the basements of the Oulongbuluke micro-blocks and the Qaidam micro-blocks are geochemically akin to that of the Yangtze Block, and that the Yangtze Block Domain can be extended northwestwards to the micro blocks on both sides of the Altyn-Tagh fault, and that the UHP-HP tectonic belt along the northern margin of the Qaidam micro-block is only a convergent boundary among the earlier broken-up micro-blocks within the Yangtze Block.