Geological And Geochemical Characteristics And Zircon U-Pb Dating Of Quartz Diorite Porphyrite Body In Ludian,Yunnan Province

The geotectonic location of the study area is located in the middle section of the Jiangda-Deqin-Weixi continental margin volcanic arc in the Jinshajiang suture zone.The widely developed magmatic rock on both sides of Jingshajiang suture zone is an important basis for the study of oceanic expansion,ocean-land subduction,and land-land collision,and it has been used to invert the structural evolution of the Jinshajiang suture zone.Through previous studies,it is found that there are many magma arcs in the Jinshajiang junction zone,but the Jiangda Deqin Weixi section is the most ideal area for studying the evolution history of the Jinshajiang junction zone.According to previous studies,it has been found that there are multiple magmatic arcs in the Jinshajiang suture zone,but the Jiangda-Deqin-Weixi section is the most ideal area for studying the land-land collision of the Jinshajiang suture zone.Many studies have been done on the Jinshajiang suture zone.However,the study of Ludian magmatic rocks is not thorough enough,and no Early Triassic magmatic rocks were found in Ludian area.Therefore,this article selects quartz diorite porphyrite in the Ludian area on the Jiangda-Weixi continental margin volcanic arc as the main research object,and quartz-monzonite as the auxiliary research object,conducts detailed field geological surveys and indoor petrography studies,and uses LA-ICP-MS zircon U-Pb dating and the analysis of the main trace elements of the whole rock are used to study the genesis type,age and tectonic environment of the rock.The geological characteristics of the rock mass show that the rock mass in the study area is divided into two stages.The first stage is quartz-monzonite,which is in the shape of rock plant and exposed near Zhongcun and Shangcun.The nearly circular intrusive body with an exposed area of about 1.6km² is divided into two facies zones.The internal facies is fine-grained quartz-monzonite,which is mainly distributed in the higher terrain and the marginal facies is medium-sized quartz-monzonite,which is mainly distributed in the higher terrain In the lower part,the mineral composition is quartz,plagioclase,potash feldspar,biotite,etc.The second stage is quartz diorite porphyrite,which occurs in the form of rock plant,and is exposed near Zhongcun.The near ellipse intrusive body with an area of about 2km² is divided into two facies belts.The internal facies is fine-grained quartz diorite porphyrite,and the marginal facies is medium coarse-grained quartz diorite porphyrite.The mineral composition is plagioclase,quartz,hornblende and biotite,etc.The geochemical characteristics of the rock mass show that the two groups of samples have low SiO₂ content and aluminum saturation index of 0.93 to 1.02.The quartz-monzonite is a potassium basalt series,and the quartz diorite porphyrite is a high-potassium calcium-alkali series.Both stages rock masses are characterized by the enrichment of large ion lithophilic elements?LILE?such as Rb;deficient in high field strength elements?HFSE?such as Nb,P,and Ti;meanwhile,both samples showed relative loss of Ba,compared with One group of samples lost Ba more significantly.Quartz-monzonite and quartz diorite porphyrite have a higher content of light rare earth elements,and a higher ratio of cut light/heavy rare earth elements.Both have the characteristics of I-type granite,and their origins are partial melting of amphibole,magma mixing and assimilation the effect of mixed dyeing is small.According to the structural discrimination of the samples,it can be concluded that both rocks are of the type of VAG?volcanic arc granite?.According to the zircon U-Pb dating test of quartz diorite porphyrite has shown that the formation age is Early Triassic?250.6±1.8Ma?.It fills in the chronological evidence of the existence of Early Triassic magmatic activity in the Ludian granite sequence of Ludian granite,and shows that the middle section of the Jinshajiang combined zone?Wexi section?has entered the subduction stage before 251Ma.And compared with predecessors'research results on the age of granites in Ludian,it is found that the southern part of Ludian entered the subduction stage earlier than the northern part.It is found that the Early Triassic intrusive body in Ludian area is similar to adakite through the study of quartz-monzonite and quartz diorite porphyrite by comparing with predecessors.Therefore,it has a certain indicating significance for looking for porphyry copper gold polymetallic deposit and skarn magnetite deposit in Ludian area.