关键词: 东昆仑造山带, I型花岗岩, 岩石地球化学, 锆石U-Pb定年, Hf同位素

Abstract:  The basic geological research of Akchukesai area in the western Segment of the East Kunlun orogenic belt is weak. The granite gneiss in this area was designated as the Jinshuikou Group by predecessors. In field work, it was found that the Jinshuikou Group gneiss should be a granite gneiss intrusion. In order to determine the geochronology and petrogenesis of the intrusion， the rock geochemistry, zircon U-Pb geochronology and Hf isotope studies were carried out in this paper. The results show that: the lithology of the sample is gneissic biotite monzogranite, major element data show that the SiO₂ content is 74.44%-76.36%, Na₂O and K₂O contents are respectively 0.06%-0.07% and 3.89%-4.35%, Al₂O₃ content is 9.76%-10.95%, A/CNK is 0.92-1.09，TiO₂ and MnO contents are respectively 0.32%-0.38% and 0.10%-0.13%；CaO content is 2.70%-3.46%，Mg^# is 25.42-29.69；The rare earth elements of the samples are higher, ΣREE is 200.04×10^-6-215.30×10^-6, LREE/HREE is 6.94-7.88. Trace elements show the characteristics of enriched in Rb, U, Th, K and Nb, Ta, P, Ti, Sr showed“V”type depleted. The age of formation is Early Neoproterozoic ((966±3)Ma，MSWD=4.1), zricon in situε_Hf(t)=-3.38-3.14, Hf isotope two-stage model ages T_DM2 range from 2 033-1 625 Ma. Petrogeochemical and Hf isotopic results show that the gneissic biotite monzogranite is peraluminous-weak peraluminous high-K calc-alkaline I-Type granite. The magma source area should be dominated by new basaltic crust, with the addition of Paleoproterozoic silical-aluminum crust, which may be the partial melting of plagioamphibole and gneiss of  Paleoproterozoic Jinshuikou Group. The petrogeochemical characteristics show that the samples were formed under the tectonic background of subduction to collision transformation in the Early Neoproterozoic. Based on the comprehensive analysis of regional tectonic background, it is concluded that Early Neoproterozoic magmatism and tectonic activity are prevalent in the East Kunlun region, which responds to the global Rodinia supercontinent convergence event. The samples studied in this study are the concrete manifestation of the collision formation of Rodinia supercontinent convergence in the western segment of East Kunlun, this indicates that the region was transitioning from subduction to collision orogenic stage at  about 966 Ma.

Key words: Eastern Kunlun orogenic belt, I-type granite, petrogeochemistry, zircon U-Pb geochronology, Hf isotopes