The Petrology And Litho-geochemistry Characteristics Of The Granitoid Rocks Of Mts.mangkangshan Area In East Tibet

Mts.Mangkangshan is located in Mangkang County,Changdu City,Tibet.The administrative division is basically under the jurisdiction of Mangkang County in Changdu City,Tibet autonomous region,and a small part of the southeast of this erea belongs to Batang County,Sichuan province.The predecessors have done many basic geological work in this area,but due to the influence of scale accuracy,job level and geoscience theory,there are still some problems:the relationship between tectonic conditions and intrusive activity of magma,the output mechanism of rock mass,the properties of magma source area and its relationship to mineralization,and the regional metallogenic geological background are lack of investigation;and the precise age of magmatic rocks in the study area is not inadequate,which affects the accurate understanding to the period of tectonic magma evolution;the research in petrology and petrogeochemistry to granite in the area is lack of systematic study,which makes the achievement research production discovered rather fragmented.Although predecessors have obtained the research achievements of granitoid rocks in this area,they have not systematically analyzed and discussed the tectonic background of the granitoid rock through these achievements,and did not use these achievements to carry out metallogenic evaluation.Therefore,this paper hopes to reveal its spatial and temporal distribution,the composition of the crustal source area and the petrogenesis through the study in petrology and petrogeochemistry to granitoid rocks of Mts.Mangkangshan area,and to restore the tectonic setting of the granitoids in the area and discuss its mineralization.The tectonic location of Mts.Mangkangshan area is located in the Changdu-Lanping block of the northern part of the Sanjiang orogenic belt,which belongs to Jiangda-Weixi arc belt of continental margin.In the region,the rock association is relatively simple,granite-porphyry and granodiorite-porphyry are in the majority.The intrusion of magma may be divided into two phases through the known two isotopic ages?38-47 Ma and 81-102 Ma?.Therefore,the main magmatic activity is the product of the plate subduction in Indosinian and the orogeny movement in the Yanshan period,which indicates that Old Tethys was closed at the end of Indosinian.In the middle of Himalaya,the oceanic plate subducted to the north and the Jinsha River ancient continental block began to crack due to the closure of neo-Tethys.After the orogenic movement,the lagging magmatic activity produced a large number of porphyry,thus the granitoid rocks of Mts.Mangkangshan area were formered.The granite in the study area is mainly intruded in Upper Triassic Adula Formation,Duogaila Formation,Bolila Formation and Middle-Lower Triassic Malasongduo Formation with irregular nervation.The lithology is mainly intermediate-acid intrusive rocks in Himalayan,including granite-porphyry,granodiorite-porphyry,quartz diorite porphyrite,and a small amount of ivernite,diorite-porphyrite and andesitic porphyrite.The sequence of granitoid magmatic evolution is:monzodiorite,granodiorite-porphyry,granite-porphyry.By analyzing the geochemical data of the samples,it can be found that the content of SiO₂ is between 66.52%-71.80%and the content of Al₂O₃ is between14.51%-15.59%According to the relationship diagram of the major element,we found that the granite-porphyry belongs to the transition region between calc alkaline series and high potassium calc alkaline series,and the granodiorite-porphyry belongs to the high potassium calc alkaline series,and the quartz diorite porphyrite belongs to the shoshonite series.According to the analysis to the spider diagram,we found that the high field strength element?HFSE?and the large ion stone element?LILE?have obvious differences.The rock samples are enriched with Rb,Th,U,K,La,Ce,Sr and other large ionic stone elements,and have a loss of high field strong elements such as Ta,P and Ti.Ba is depleted which is relative to Rb and Th.Combined with the values of Nb*,K*and Sr*,it is suggested that granitic rocks may be formed in the island arc area.Through the analysis of the geochemical characteristics of rare earth elements,we found that the distribution curve of the rare earth element chondrites is inclined to the right,the value of?La/Yb?_N is more than 1,and there is slight Eu negative anomaly,which indicates that the granitic rocks of Mts.Mangkangshan area may belong to the crustal remelting type?S type?,and the enrichment of light REE may show the potential of mineralization.The age data obtained from U-Pb Zircon Dating is 36.41±0.3Ma?MSWD=1.19?,which indicates that the magmatic activity in this area is late Eocene.Through the analysis of the major and trace elements of granite in Mts.Mangkangshan area,and combining with the zircon U-Pb age data and the chemical characteristics of the granite rock,it is found that the granite in Mts.Mangkangshan area belongs to post-COLG.The deposits related to granites of Mts.Mangkangshan area are mainly porphyry copper-molybdenum deposits and skarn copper deposits.The geophysical and geochemical anomalies in the study area show more mineralization background related to Cu,Mo,W,Sn and Bi and so on.It shows that there are the geochemical background conditions of copper,molybdenum,tungsten,tin and other metallogeny of Mts.Mangkangshan area.Moreover,the enrichment of LREE indicate this erea may have potential for mineralization from the geochemical characteristics of rare earth element.