Reworking of the Juvenile Crust in the Late Mesozoic in North Qinling,Central China

The Qinling Orogen resulted from the collision between the North and South China blocks in the Triassic.Mesozoic granitoids,ranging from the Triassic to the Cretaceous,are widely distributed in this orogen,and they provide excellent clues for understanding the crustal evolution and geodynamic evolution of the orogenic belt.The Triassic belt is mostly located in the South Qinling,whereas the Cretaceous belt is located mostly in the North Qinling.The Taibai complex pluton is located at the conjunction of the two belts.Here we present a data set comprising zircon U-Pb dating and elemental and Sr-Nd isotopic geochemistry for Late Mesozoic granite and microgranular enclaves(MME)exposed in the Taibai complex pluton.The granite and MME yield concordant U-Pb zircon ages of 124 to 118 Ma,indicating that they were products of roughly simultaneous magmatism in the Late Mesozoic.The granite rocks are high-K,calc-alkaline,and weakly peraluminous in compositions,and they are characterized by enrichment in large ion lithophile elements(e.g.,Rb,Ba),depletion in high field strength elements(e.g.,Nb,Ta,Zr,Ti),and variable Sr/Y ratios of 7.64 to 63.6.Low MgO,Cr,and Ni contents imply that the magma(s)were essentially crust-derived.Both the granite and the MME show relative depletion in Sr-Nd isotopic composition(initial ^(87)Sr/^(86)Sr of 0.7044 to 0.7067,initialε_(Nd) values of-3.4 to-2.6),suggesting that the magma(s)originated from juvenile crustal rocks.These Sr-Nd isotopic characteristics are significantly different from those of other Late Mesozoic granitoids exposed elsewhere in the Qinling orogenic belt,which formed from much older and enriched sources and with negligible contributions from mantle or juvenile crust.We propose a reworking event of the juvenile crust during the Late Mesozoic that was triggered by the tectonic extension and subsequent asthenospheric upwelling that occurred in eastern China.