| The Gulungou region located in the northern margin of Yili-Central Tianshan bloc k which with a large-scale complex batholith of granitoid. The detailed geological, geo chemical and zircon Hf isotopes characteristic as well as LA-ICPMS zircon U-Pb dati ng of the granitic batholith have been carried out in this thesis.The granitic batholith of Gulungou region, in which two periods and three stages of intrusions took place, respectively to the Early Ordovician granodiorite porphyry, t he Late Ordovician mica monzonitic granite, and the Early Carboniferous quartz diorit e represented. The LA-ICPMS zircon U-Pb ages of mica monzonitic granite is449.3M a. Its geochemistry features are:high SiO2, Na20, Al2O3, and Sr contents, low MgO, Y, and HREE(Yb) contents and high Sr/Y ratio, together with weak to medium negati ve Eu anomalies and obvious fractionation between LREE and HREE, similar to Na r ich adakitic rocks. In addition, its Zircon Hf isotopic compositions are176Hf/177Hf=0.282403～0.282677, εHf(t)=3.5～6.3and TDM2=1417～914Ma, show their crust mantle mixed origin. All these suggest that the source-rock of the Late Ordovician mica monzonitic granite is the crust-derived connection basaltic mixing magma come from the mantle d erived magma invasion in the Mesoproterozoic Lower Crust. So, this article thinks:th e Late Ordovician mica monzonitic granite have the relations with subduction action o f the ancient oceanic crust shell plate in Ordovician period. It is the product of partial melting under the condition of shell cut, active continental margin of rich Na crust c onnection basaltic rock bottom in amphibolite-eclogite facies.The LA-ICPMS zircon U-Pb ages of quartz diorite is331.8Ma. Its geochemistry characteristics are:rich SiO2, Al2O3, Na2O, low TiO2, K2O and poor alkali, belongs to quasi-aluminous and calc-alkaline I type granite. Enrichment of LILE, LREE and loss ing HFSE, HREE and obvious characteristic of Nb and Ta, Ti, P negative abnormal c haracteristic indicate that it belongs to volcanic arc granite. High CaO, TFe2O3, MgO and Mg#, and characteristics of trace element such as Nd/Th, Nb/Ta, Ti/Y and Ti/Zr, together with Zircon Hf isotopic compositions(176Hf/177Hf=0.282662～0.282777, εHf(t)=2.9～7.4, TDM2=985～767Ma), show the strong mark of mantle-derived magma. All these c haracteristics suggest that the Early Carboniferous quartz diorite was formed by partial melts of young lower crust consisting of island-arc volcanic rocks, resulting from the underplating of mantle-derived basic magma.The formation of mica monzonitic granite have the relations with subduction actio n of the Junggar-North Tianshan ocean in Ordovician to the Early Silurian period. Un der the background of subduction, asthenosphere basaltic magma of the lithosphere ma ntle upwelled and invaded basaltic rock at bottom of the Neoproterozoic Na rich crust at the environment of active continental margin oweing to the breaking off of the su bduction plate, inducing it to partial melting to form the Late Ordovician mica monzo nitic granite. The northern West Tianshan region even the whole Tianshan area belong s to the extensional tectonic setting in the Carboniferous to the Early Permian. The E arly Carboniferous quartz diorite is probably a product of granitic magma from partial melting in the young lower crust which underplated by mantle derived magmas. The lower crust consisting of island-arc volcanic rocks. So partial melting to form the Ea rly Carboniferous quartz diorite which suffered the invasion of mantle magma inherite d and the geochemical characterristics of the volcanic arc volcanic rocks.Furthermore, this thesis also thinks:the Late Ordovician mica monzonitic granite and the Early Ordovician granodiorite porphyry are related to subductiongenerated plut onism at plate margins. Together with geochemistry features of the two kinds of grani toid, showing that the Gulungou region has the favorable geological setting for porphy ry copper desposit mineralization. |
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