Paleozoic Tectonic Evolution,diagenesis And Mineralization Of The Zhaheba And Its Adjacent Areas In East Junggar,Xinjiang

The eastern Junggar region is located in the north of Xinjiang,China.As an important part of the Central Asian orogenic belt(CAOB),Its tectonic evolution is an important research topic of Phanerozoic continental growth and paleo Asian Ocean evolution in the CAOB.Since Paleozoic,the area has experienced the tectonic evolution history of ocean expansion,plate subduction,collision and post collision,forming a series of island arc complex belts and accretion complexes.A lot of research work has been done on the plate boundary,material composition,basement properties,closure time of ocean basin and mineral development characteristics of eastern Junggar,and a lot of progress and consensus have been achieved.However,there are many different opinions on the Paleozoic tectonic attribute,tectonic evolution model and evolution time in this area.In the study of typical deposits,there is no systematic study on the spatiotemporal distribution of diagenesis and mineralization and regional metallogenic process.In this paper,Zhaheba and its adjacent area in the northern margin of East Junggar are selected as the research object.Based on the detailed field geological survey,the Paleozoic diagenesis and mineralization in dure and its adjacent area in the northern margin of East Junggar were systematically studied in the aspects of petrology,mineralogy,chronology,petrochemistry and isotope geochemistry.The regional geological background was summarized,and the spatial and temporal distribution characteristics of Late Paleozoic magmatic rocks were revealed,the ages of diagenesis and mineralization are discussed,the characteristics of magmatic rocks,the origin of magmatic rocks and the key scientific problems of geotectonic environment and regional mineralization are discussed,so as to provide new information for the Paleozoic tectonic evolution and diagenesis and mineralization in eastern Junggar.The main achievements and understandings are as follows:1.Petrology and geochemistry of each rock unit of Zhaheba ophiolite have been studied through 1:10000 geological section.Geochronology of Yundukara Cu-Au-Co ore bearing rock mass in Zhaheba ophiolite has been studied.The age of Yundukara ore bearing diorite and gabbro-diorite is 401 Ma,which is far less than the formation age of Zhaheba ophiolite(488?498 Ma).Each rock unit in Zhaheba ophiolite has geochemical characteristics influenced by subduction fluid,which shows a gradual maturation process of intra oceanic island arc.Zhaheba ophiolite was formed in the fore arc environment above the subduction zone(SSZ).The products formed later,such as Yundukala ore bearing diorite,gabbro diorite and diorite porphyrite,are the products of subduction in different periods.2.Yundukala ore bearing diorite and gabbro diorite belong to calc-alkaline and high-k calc alkaline series,and they are peraluminous rocks with medium Mg#(0.39?0.50).They are rich in large ion lithophile elements Rb,U,K,and depleted in high field strength Elements Nb,Ta,Zr,Hf.The whole rock(⁸⁷Sr/⁸⁶Sr)_i is 0.704966?0.707395,the?_Nd(t)is 1.29?3.84,the zircon?_Hf(t)is-1.7?18.8,with an average of 5.6,and the?¹⁸O is 5.25‰?10.17‰,with an average of 7.71‰.The ore bearing diorite and gabbro diorite in Yundukala were formed in an island arc environment.The magma source area was mainly from depleted mantle,and about 20%?40%of crust source material was contaminated.The zircon U-Pb age of the two samples is about 401 Ma,and both of them capture the old zircon of Precambrian,which indicates that there may be an old Precambrian basement in this area.3.The Devonian intrusive rocks are distributed in a small area,but the volcanic rocks are well developed.The age of ore bearing quartz diorite in Yuyitas deposit is 384.6ma,the age of Suodong hornblende gabbro is 387.2 Ma,the whole rock(⁸⁷Sr/⁸⁶Sr)_i is 0.703512?0.704076,the?_Nd(t)is 4.98?5.36,the zircon?_Hf(t)is 9.8?12.9,and the?¹⁸O isotope is 6.32‰?6.66‰.The ages of Kalazhela limburgite and alkaline basalt are 393.5 Ma,with apatite(⁸⁷Sr/⁸⁶Sr)_i ranging from 0.703066 to0.703332 and?_Nd(t)ranging from 5.26 to 7.51.The study shows that the tectonic setting is subduction environment related to intra oceanic arc.The magma source area of Suodong hornblende gabbro and Yuyitas ore bearing rock body is mainly from depleted mantle,which is formed by subduction plate fluid and subduction sediment melt metasomatic upper mantle wedge under island arc background.The source areas of limburgite and alkaline basalt are derived from depleted mantle and less polluted by crust,which may be the product of garnet peridotite melting.4.The Carboniferous Permian intrusive rocks are well developed in this area,but the volcanic rocks are generally developed.The age of the Zhaheba west pluton in the alkaline granite belt is 321Ma,which is earlier than that of the Kalamaili alkaline granite belt.It has the geochemical characteristics of A2 type alkaline granite.The tectonic setting is a post collisional environment,suggesting that the orogeny in the area was over when it was emplaced.From early to late,the TDM2of A-type granites in the Wulungu kalamaili area of eastern Junggar gradually decreased,while the value of?Nd(t)gradually increased,indicating that the CAOB continued to accretion southward.The zircon ages of the Kulabiye ore bearing body and the ore bearing rhyolite of the Kalagang Formation are 274?278Ma.The major and trace elements and Sr-Nd-Hf isotopes show that the former is mainly derived from depleted mantle with the addition of crust source materials,while the latter and Zhaheba west alkaline granite are the products of remelting of newly accreted young crustal materials in depleted mantle.5.The Paleozoic tectonic evolution in eastern Junggar can be divided into four stages:The late Cambrian to Early Ordovician(503?480Ma)is the ocean spreading stage,the early Ordovician to Early Carboniferous(480?360Ma)is the subduction stage,the Early Carboniferous to Late Carboniferous(360?330Ma)is the collision stage,and the Late Carboniferous to Permian(330?252Ma)is the post collision stage.The ore-forming processes are as follows:chromite deposits related to ophiolite in Ordovician,copper polymetallic deposits related to intermediate acid and intermediate basic rocks in Devonian,copper deposits related to intermediate acid rocks in Carboniferous,Cu-Ni sulfide deposits related to basic ultrabasic rocks in Permian,hydrothermal gold deposits related to shearing in Permian,fluorite,perlite and other nonmetallic deposits related to rhyolite in Permian.