Magmatism And Metallogeny In The East Kunlun Orogenic Belt

The East Kunlun Orogenic Belt,belonging to the northern part of Qinghai-Tibet plateau,is located in the southern margin of the Qaidam Block.It is divided into eastern and western sections by Wutumeiren Town.The west segment is Qimantagh area and the eastern segment concentrates in Dulan area.Silurian-Devonian magmatism emplaced widely in the west segment of the East Kunlun Orogenic Belt,Previouse studies mainly focused on the Triassic metallogeny and the detailed research on porphyritic complexes associated with porphyry mineralizations are still remaining to be done.In this study,numbers of porphyries and porphyry mineralizations outcropts have been observed in the eastern segment and also two aspects of achievements are obtained which are given as follows.Through the intergated studies on petrography,petrology,rock geochemistry and zircon geochronology from five Silurian-Devonian granitic plutons in west segment,as well as the combined data and evidence from previous studies,it indicates the multiple magmatic events,and also provides the new insights for the petrogenesis and tectonic setting in Silurian-Devonian,leading to a intergated model of tectonic evolution.Magmatism occurred at least at four stages in the Qimantagh and coincide with four pulses of magma events including the Late Silurian Wulanwuzhuer potassium granite(421.2±1.9 Ma)and Nalingguole monzogranite(420.6±2.6 Ma),Early Devonian Yemaquan granite-porphyry(403.7±2.9 Ma),Middle Devonian Qunli granite porphyry(391.3± 3.2 Ma),and Late Devonian Kayakedengtage granodiorite(380.52±0.92 Ma).It is the first report on the granodiorite pluton in Kayekedengtage area during the Late Devonian.The granites which formed at ca.421 Ma to 408 Ma show high-k calc-alkaline and clear peraluminous affinity suggesting the tipical geochemical features of S type granite as well as those in I type granite with the affinity of high-k calc-alkaline and aluminium-weakly peraluminous.In some case,few granite samples show the characters of A type granite formed in extensional setting with the mostly absence of magma invasion and magma mingling.The mantle-derived magma might be the possible heat source.Extensive magma invasion and magma mingling occured from ca.408 Ma-380 Ma.Qimantagh had undergone an intracontinental collision orogenic process(the post-collision tectonic setting)during Late Silurnian to Late Devonian.In this study,we also selected the eastern segment as the most important sector and carried out systematical research work on petrography,petrology,rock geochemistry and zircon chronology of massive Mesozoic porphyry,and ascertain the petrogenic age of porphyry,magma source area and tectonic setting.The article has determined the metallogenic epoch,the ore-forming material sources and metallogenic tectonic background of these porphyry deposits.On this basis,this paper elaborates the typical deposit ore-controlling factors and prospecting criteria,and probes into the ore-forming process of the porphyry deposits.In addition,the paper analyzed the uplift and denudation of the eastern segment from the fission track dating angle.Details are as follows:This study confirmed a large number of porphyry originally classified as Yanshan period(Jurassic)which should belong to Indosinian(Triassic).The formation of porphyry mainly occured in 251-230 Ma.Early-Middle Triassic(251-236Ma)porphyry belong to metaluminous-peraluminous high K calc-alkaline series,and possess right curve with enriching in LREE,losing HREE,moderate Eu negative anomaly(?Eu = 0.37-0.79),and riching elements(Rb,Ba,Th,and K)and depleting high field strength elements(Ta?Nb?Hf?Zr?Y and Yb).Magma derived from the partial melting of mafic lower crust,and was suffered from mantle source material.Late Triassic(about 230 Ma)porphyry belong to peraluminous high K calc-alkaline series,and possess V curve with significant Eu negative anomaly(?Eu =0.03?0.30)and intensively losing Ba?Sr?P?Eu and Ti.Magma mainly derived from the partial melting of crust,and mantle source material did not participate in the process.Indosinian period is an important period for porphyry deposits.They are at least two metallogenic process: One formed in the active continental margin environment of Animaqing ocean northward subduction process in the Early Indosinian;The other formed in the collision-post collision transition environment in the Late Indosinian.More work needs to be further carried out to prospect for the concentration area of eastern hydrothermal and skarn deposits,and eventually establish regional metallogenic model of eastern porphyry deposits.The average denudation rate of the eastern segment is 0.027 mm/a,and there are the different denudation for various area.South Kunlun tectonic belt is relatively simple,there is once rapid cooling uplifting event between 130 and 75 Ma.Middle Kunlun tectonic belt is relatively complicated,and there are at least twice rapid cooling uplifting events at ca.130-105 Ma and ca.20 Ma.The tectonic belt of North Kunlun fault is most complicated,first is the occurrence of rapidly colling and uplifting in the southern part at.ca.130-105 Ma,and then northern partrapidly cooled down and uplift at.ca.105 Ma-75 Ma.But there are still at least twice rapid cooling uplifting events at ca.130-75 Ma and ca.20 Ma.