Geochronology,Geochemical Characteristics And Geological Significance Of Quartz-diorite From The Huogeqi Area In Inner Mongolia

The Huogeqi copper deposit in Inner Mongolia is located in the Cu-Pb-Zn polymetallic metallogenic belt of Langshan Mountain,which is located in the western part of the northern margin of the North China block.In recent years,scholars have studied Hercynian intrusions in detail and accumulated abundant data in this area.Most of the research focuses on the genesis of intrusions and deposits,neglected geochemical characteristics,formation age,source of magma and tectonic geological background.In view of this,choosing quartz-diorite in this area as the research object the paper selects,through the study of its chronology,geochemistry and Lu-Hf isotope,we will discuss the genesis and tectonic setting of quartz-diorite that confirm the age of its formation and explor the relationship with the Huogeqi deposit.and provide the chronological data for the closure time of Paleo-Asia Ocean.The quartz-diorite in Huogeqi area is ashen to celadon,in semi-self-shaped granular structure and massive structure.The main mineral is plagioclase,hornblende,quartz biotite,and the accessory minerals is apatite,zircon and so on.Analytical results show that Huogeqi quartz-diorite contains the geochemical characteristics of low silicon,P₂O and high Mg O the value of A/CNK is between 0.79 to 0.89,and A/NK between 2.50 to 2.92.The A/CNK and A/NK all belong to metaluminous-cal-alkaine series.The contents of rare earth elements in rocks is low,but between light rare earth elements and heavy rare earth elements have remarkable fractionation and the samples show slight positive Eu anomaly,and there is no Ce anomaly.The trace elements are rich in Rb,K,Sr and Sm,but relatively deficient in Ba,Ta,Nb,Zr,Ti.Comprehensive analysis shows that quartz-diorite has the characteristics of I-type granite.Electron microprobe analysis shows that plagioclase is mainly feldspar has little change in composition.The amphibole in the rock is mainly magnesia amphibole.According to the calculation of amphibole temperature and pressure,the crystallization depth of minerals in quartz-diorite is between 15.18 km to 22.11 km,and the emplacement depth of magma is between 2.2 km to 5.0 km,which indicates that quartz-diorite is hypabyssal intrusive rock.The LA-ICP-MS zircon U-Pb dating results show that two quartz-diorite samples were formed at 270±4 Ma and 273±1 Ma,respectively,which were the products of the Middle Permian magmatism.The zircon(Y33)Hf isotope data show that?Hf(t)is between-11.78 to-0.77,and the corresponding two-stage mode age is between 1352 to 2044 Ma,indicating that the quartz-diorite magma original as Paleoproterozoic era crustal material.According to the discriminating map of the amphibolite magma source area,it is considered that a small amount of radon material is mixed in the magma.Based on previous research results of the region and according to the quartz-diorite tectonic settings and the formation era,it is confirmed that the quartz-diorite in the Huogeqi area is formed on the active continental margin under the subduction background,and the Paleo-Asia Ocean is still subducting southward.The final closure should be after the Middle Permian.