Zircon U-Pb geochronology and geochemistry of the Mayile ophiolitic mélange in West Junggar and implications for source nature
西准噶尔玛依勒蛇绿混杂岩锆石U-Pb年代学、地球化学及源区特征

Precise zircon U-Pb dating and geochemical composition analysis on the ophiolitic mélange belts in West Junggar. It is a clue for forming and evolution of the pale-ocean, rebuilding palaeotectonics and tracing the source of magma source. LA-ICP-MS zircon U-Pb weighted mean 206Pb/238U age of the gabbros from the Mayile ophiolitic mélange in the West Junggar is 572.2±9.2Ma, belong to Early Sinian, this is oldest age from ophiolitic mélange in the Junggar as well as North Xinjiang. The alkalic pillow basalts from Mayile ophiolitic mélange are similar with the ocean island basalt (OIB), characteristics by high Ti (TiO2=1.65%~3.13%), Fe (FeOT=8.93%~18.11%), Mg (MgO=3.95%~5.27%) and P (P2O5=0.17%~0.51%), and high Th/Ta ratios (1.1~1.9), and clear differentiation between LREE and HREE ((La/Yb)N=2.5~7.4). It is assumed that the magma extruded into ocean island or seamount of the ocean floor. However, the geochemical characteristics of the gabbros different from basalts, may be form subduction-related setting. The geochemical features of the basalts show they have ocean island basalts, derived from EMI type enriched-mantle. Petrogenesis is closely related to asthenosphere mantle, asthenospheric mantle upwelling led to a large proportion of spinel lherzolite mantle partial melting to forming the basalt magam. It is a product of asthenosphere interacted with lithosphere.