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Reworking of the Tarim Craton by underplating of mantle plume-derived magmas: Evidence from Neoproterozoic granitoids in the Kuluketage area, NW China

Abstract:

Most Neoproterozoic granitoids in the Kuluketage area, northern Tarim Craton are characterized by strongly depleted HREE abundances and high Sr/Y and (La/Yb)N ratios, showing typical geochemical features of adakitic rocks. Zircon U-Pb dating of three adakitic plutons yielded Neoproterozoic ages (754±4, 790±3 and 798±3 Ma). The adakitic granitoids exhibit low MgO and TiO2 contents. Their low Cr, Co and Ni abundances, low e{open}Hf(t) values (-21 to -11) and high FeOT/MgO ratios (mostly 2.2-2.9) preclude the possibility of being derived from partial melts of delaminated lower crust. The relatively low e{open}Hf(t) values and old Hf two-stage model ages (TDM2=2.42-3.02 Ga) of the adakitic granitoids are similar to those of the basement rocks in the northern Tarim Craton, suggesting that the adakitic rocks were generated by partial melting of basement rocks in a thickened lower crust. Apart from the adakitic granitoids, Neoproterozoic normal I-type granitoids with low Sr/Y and (La/Yb)N ratios are also exposed in this area, and their geochemistry indicates a crustal origin at a shallower depth. Zircon U-Pb dating of the I-type granitoids also yielded a Neoproterozoic age of 785±8 Ma. The petrogenesis of the Neoproterozoic adakitic granitoids suggests that Neoproterozoic crustal thickness in the northern Tarim Craton must have been over 50km. In combination with the occurrence of coeval mantle-derived dykes and bimodal volcanic rocks, a partial melting scheme triggered by underplating of mantle plume-derived magmas is proposed to interpret the formation of the Neoproterozoic adakitic and I-type granitoids. This model provides an alternative interpretation for the Neoproterozoic craton reworking happened in the Rodinia supercontinent. © 2011 Elsevier B.V.