Geochemistry and Genesis of Monzonitic Granite from Aikengdelesite Area in East Kunlun, Qinghai

The Aikengdelesite Cu-Mo deposit is a newly discovered porphyry deposit in the southern compound margin of East Kunlun.The ore bodies are found in granite porphyry and broken monzonitic granite.Based on the studies of geochemistry and Sr-Nd isotope, this paper mainly discusses the petrogenesis, magma source, tectonic setting of the monzonitic granite.The results show that the monzonitic granite is characterized by high SiO₂and Na₂O, low MgO and CaO contents, belonging to calc-alkaline and peraluminous series groups.The trace elements show the enrichment in LILE (such as K, Ba and Rb)and mobile incompatible elements (such as Th, U), but they are relatively depleted in HFSE (such as Nb, Ta, P, Ti).The results of I_Sr ratios range from 0.707 05 to 0.707 37, and ε_Nd(t)values vary from -2.2 to -1.6, as well as Rb/Sr ratios from 0.17 to 0.32, indicating that the monzonitic granite was derived with crust-mantle mixed magma.After analyzing the Y+Nb-Rb and La/Nb-Ba/Nbdiagrams, and the Ophiolite belt occurred with ocean subduction, it is suggested that the monzonitic granite was formed in Andean-type active continental margin.Subduction leaded to the subducting slab fluids lower the melting point and directly replace mantle, and then the mantle occur the partial melting to form the basic magma.The basic magma underplated and provided thermo-power.The Aikengdelesite monzonitic granite was finally formed by the partial melting of basic lower crust, which was mixed a small amount of mantle-derived magma.