Silurian-Devonian Intrusive Magmatic Rock And Ore-Bearing Potential In The East Kunlun Orogenic Belt,Qinghai Province,China

The study of geodynamic evolution is very important to endogenetic deposits.Due to its unique geological conditions,plate margins has become an important object to explore the relationship between mineralization and plate tectonics and magmatic.As an important part of the Tethys tectonic domain,the East Kunlun orogenic belt(EKOB)has experienced proto-tethys,paleo-tethys and neo-tethys.With the end of the proto-tethys evolution and the beginning of the paleo-tethys evolution,magmatic Cu-Ni sulfide deposits represented by Xirihamu,Langmuri and Gayahedonggou were formed in the belt.The skarn polymetallic deposits associated with intermediate-acid intrusive rocks are represented by Larangmai,Kaerqueka and Yemaquan.EKOB Cu-Ni polymetallic resource base has established an important position.Because many controversies in the study of metallogenic geological background,especially the theoretical study of tectonic evolution in the process of proto-tethys ocean closure and paleo-tethys ocean cracking is relatively weak,the metallogenic regularity of magmatic rocks related to it is also in the exploration stage,and the tectonic indication significance of mineralization has not been deeply explored.So,analyze structural belt of EKOB Silurian-devonian magmatic regularity and mineralization is particularly important,not only can provide a key basis for reconstructing the tectonic stage division of proto-tethys and paleo-tethys metasomatism process,but also help to Cu-Ni sulfide deposits,skarn deposits metallogenic model,thus further to guide the prospecting work deployment.This paper is based on the combination of tectonics,magma and mineralization.The aim of this study is to analyze the intermediate-acid,mafic and ultrabasic intrusive magmas and related typical deposits widely distributed in the Silurian to Devonian tectonic belt.On the basis of the original research,according to the activity law of magmatic rocks,the tectonic evolution and mineralization stages are divided into the ocean-land transition during the closure of proto-tethys ocean and the prelude of the breakup of the paleo-tethys Ocean,which provides a certain basis for the study of regional geological evolution and mineralization laws.The main achievements are as follows:(1)Silurian to Devonian granitic intrusive rocks in EKOB generally have the geochemical characteristics of subduction zone.The temperature of granitic magmatic liquidus gradually decreased from900~1000℃ to 700~800℃,and the differentiation index(D.I.)of magmatic rocks gradually increased.The rock types evolved from potassic basalt to high-k calc-alkaline series to calc-alkaline series to low-k series,and formed the quasi aluminum,peraluminous,partial aluminum gradient characteristics.In this study,we found that tonalite(422.3±1.9 Ma)in Harizha area,granodiorite(409.8±2.4 Ma)in Tuolahaihe area,quartz diorite(410.2±3.5 Ma)in Gayahedonggou area,granodiorite(395.9±1.4 Ma)and syenogranite(397.7±1.8)Ma)in Wulonggou area,ares I-type granite.Plagiogranite(421.5±5.0 Ma)in Lalangmai area and granodiorite(423.8±4.3 Ma)in Hariza area are S-type granites.The tonalite(422.6±1.9 Ma)in Lalangmai is adakite.The basic-ultrabasic intrusive rocks are mainly formed at 450 Ma~410 Ma,and also have the characteristics of subduction zone component contribution.In this study,the age of the Langmu dipyroxene peridotite and gayahedonggou wehrlite is 420±1.4 Ma and 419.9±1.5 Ma,respectively.The magma originated from the loss mantle and was mixed with crust materials.(2)According to the characteristics of intrusive magmatic rocks and related geological markers,such as bimodal volcanic rocks,eclogite and molasse formation,the Silurian to Devonian tectonic evolution of EKOB can be divided into three stages in this study: Ocean crust subduction(485 Ma~436 Ma),continental collision(436 Ma~420 Ma),crustal thinning and rifting(420 Ma~385 Ma).The intrusive rocks during oceanic subduction are mainly I-type granite,adakite and a small amount of diorite.Basic-ultrabasic intrusive rocks are mainly gabbro and diabase.The intrusive magmatic rocks during the continental collision stage are mainly S-type granites and highly differentiated granites related to the collision,while I-type,A-type granites and adakite appear simultaneously.The intrusive magmatic rocks in crustal thinning and rifting stage are mainly A-type granite and I-type granite,and MMEs are widely distributed in I-type granite.The basic-ultrabasic rocks formed in the same period are mainly distributed in magmatic Cu-Ni sulfide deposits.(3)The orogenic gold deposits in EKOB were enriched in Silurian and Devonian to a certain extent,which may be caused by partial melting of oceanic crust deep into the subduction zone,and the adakite enriched in gold elements was formed under the condition of high oxygen fugidity.The gold mineralization age of Lalangmai and Haxiyatu deposit is later than continental collision,and the ore-bearing mother magma may be formed by the melting of residual oceanic crust or subduction plate window.Continental collision stage,the intrusive magmatic rocks were dominated by W-Sn mineralization(427 Ma~420 Ma).During this period,the upper crust partially melted,forming the initial granitic magma rich in W and Sn.During the magma rising and emplacing process,W and Sn elements were continuously extracted from the surrounding rock,and the ore-bearing hydrothermal fluid continued to be enriched.Skarn mineralization occurs under favorable surrounding rock conditions.Crustal thinning and rifting stage(420 Ma~385 Ma)intrusive magmatic mineralization can be divided into two types.(1)Fe-Cu-Pb-Zn mineralization of intermediate-acid intrusive rocks(410 Ma~390 Ma): In the process of crustal weakening,large scale mantle magma emplacement carried ore-forming elements mixed with crust magma,and skarn mineralization formed skarn Fe-Cu polymetallic deposits such as Kaerqueka and Yemaquan.(2)The basic-ultrabasic intrusive Cu-Ni sulfide mineralization(420 Ma~405Ma): Accompanied by thinning crust,mantle plume upwelling not only provides the crust thinning and formation of rift environment outside the power,as well as Cu-Ni metallogenic provides a huge amount of magnesium iron melt,formed the early large magma chamber,under the condition of low oxygen fugacity,crustal material mixed with massive sulfide melt-after immiscible(liquation)of silicate magma,Then the magmatic Cu-Ni-Co sulfide deposit related to the basic-ultrabasic intrusive rocks was formed by uptransgression and penetration.(4)The proto-paleo tethys evolution was not continuous,and there was an obvious transition process between the ocean and the continent.The Xiarihamu and Gayahedonggou magmatic Cu-Ni sulfide deposits were formed in rift environment,which,together with the maoniushan Formation bifid volcanic rocks and regional A2-type granites,should be regarded as the mark of the paleo tethys ocean cracking.The regional evolution entered the paleo tethys stage from about 420 Ma.(5)The basic-ultrabasic and intermediate-acid intrusive rocks formed after 420 Ma generally have subduction arc geochemical characteristics,showing negative anomalies of trace elements Ta,Nb and Ti,but this does not mean that they were formed in a subduction environment.During the subduction of the proto-tethys ocean,a large number of solute components entered the mantle wedge due to the dehydration and metasomatism of mantle peridotite in the subduction zone,which changed the original properties of asthenosphere,and the magmatic rocks with the modification of asthenosphere have the geochemical characteristics of the subduction zone.