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

Abstract

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 TDM and εNd 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 TDMare 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 (206Pb/204Pb)t, (207Pb/204Pb)t and (206Pb/204Pb)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.