Studies On Triassic Tectonic Magmatism And Relationship With Mineralization In Yemaquan Area,East Kunlun

Yemaquan area is located in the Qimantage area of East Kunlun orogenic belt.This area underwent complex geological evolution and strong magmatism in Triassic,when mineral deposits are strongly formed.Based on spatial and temporal distribution,field geological,petrographic,geochemical characteristics,tectonic setting of magmatic rocks,and analysis of the regional metallogenic and typical deposits characteristics,this article mainly discuss magmatism and relationship with mineralization in Yemaquan area.Some results are concluded as following:(1)Intermediate-acidic intrusive rocks are widely developed in Yemaquan area,and its isotopic ages are concentrated in middle-late Triassic.Volcanic rocks are the part of Elashan group and are mainly intermediate-acidic volcanic and volcaniclastic rocks of a land phase.(2)Intrusive rocks in Yemaquan area are mainly belong to calc-alkaline and high-potassium calc-alkaline I-type and A-type granites.The rocks are alkali meta aluminous granite and weakly peraluminous,and some appear strongly peraluminous.From early period to late period,compositions of intrusive rocks are gradually enriched in SiO2,K2O,and reduced in Na2O,Fe2O3,FeO,MgO,MnO and CaO.The magma differentiation degree is also increased,and tends to evolve to be more mature from early to late.The instrusive rocks have similar primitive mantle-normalized trace elements spider diagram,with strong enrichment of LILE Rb,Th,U,K,Pb,moderate enrichment of HFSE Ta,Zr,Hf,REE,and depletion of Ba,Nb,P,Ti.Chondrite-normalized REE distribution pattern diagram of all intrusive rocks show negative Eu anomalies,indicating the similarity of the rocks formation.(3)The late Paleozoic-early Mesozoic orogenic cycle is composed of four stages:the formation and spreading of oceanic basin(C1-C2),the subduction(C3-T1),the syn-collision(T2-T3)and post-collision(T3-early period of J1).Isotopic ages of instrusive rocks are concentrated in middle-late Triassic and they are formed at the syn-collision and post-collision settings.According to isotopic ages of instrusive rocks,the time of syn-collision stage is defined as 240.5-223.5 Ma and the time of post-collision stage is defined as 223.5-204 Ma.Rock assemblages formed at the stage of subduction are mainly quartz monzonite diorite,quartz monzonite,diorite,granodiorite;early period of syn-collision stage are granodiorite,granite;late period of syn-collision are adamellite,porphyritic adamellite;early period of post-collision stage are adamellite,moyite;late period of syn-collision are monzonitic granite porphyry and granite porphyry.(4)There are three polymetallic mineralization types of skarn,porphyry and hydrothermal deposits in Yemaquan area.Polymetallic mineral deposits are formed in middle-late Triassic and are closely related to intermediate-acid intrusive rocks of the same peroid.Skarn-type mineral deposits are formed at the stage of syn-collision,and are closely related to diorite,granodiorite,adamellite and porphyritic adamellite.Hydrothermal and skarn-type deposits are always symbiotic together and are formed at the early period of post-collision stage,related to adamellite and moyite.Porphyry deposits are formed at the late period of post-collision stage and are closely related to granite porphyry.(5)Yemaquan area has experienced the mixing between underplating mantle-derived basic magma and crust-derived magma in Triassic,which brings a wealth of mantle-derived ore-forming components for mineralization.This could be the fundamental cause for that polymetallic mineralization is relative to tectonomagmatism of Triassic inYemquan area.