Geochemical And Isotopic Geochronology Of Mesozoic Granites In The Banjiashan Area, Inner Mongolia

The Banjiashan area is located in the eastern part of Inner Mongolia,China-Mongolia border.Plate tectonics position,located in the south of the Siberian continental margin hyperplasia plate parts,joint north of the North China craton and the Pacific Rim with the volcanic activity.In this area,because of the strong tectonic activities in the Mesozoic,large-scale magmatic intrusion and large-scale regional ore formation have always been the hot spots of scientific research.The area is rich in rock types,but its division is confusing and the disintegration of rock mass is not enough.Therefore,the basic geochemical and isotopic geochronological studies of the granite in this area are of great significance to the Mesozoic structural evolution in this area.Through the field mapping,profile measurement,and microscopic observations,we have known the rock mass of Banjiashan.The main lithology of this rock body is positivity granite,and the mineral composition is quartz,potassium feldspar,plagioclase and a small amount of biotite.The result of artificial heavy sand test is that the sub-mineral combination type is zircon-magnetite-apatite type,which has good indication significance for mineralization.From the early to the second time,the evolution of the structure of the unit followed the rules of fine grain?fractured fine grain?less spotty fine grain?spotty coarse grain,and the lithology difference was only due to the differentiation of magma evolution.The ICP-MS zircon U-Pb dating results,139.8�1 Ma,136.4�1.4 Ma,and 136.3�1.1 Ma.Accurately shows that the age of rock mass emplacement in this area was Early Cretaceous,and the original Late Devonian mapping unit did not exist.Through the study of rock chemistry and rock geochemistry,the granite rocks in this area are peraluminous,high-potassium,calcium-alkaline and high-I isotopic I-type granites.Eu has a moderate negative anomaly,light rare earth is significantly enriched,trace elements are right-leaning,and has a four grouping effect.The magmatic generative discriminant diagram is FG type granite;Nd/Ta,La/Nd,La/Ta values reflect the source of diagenesis of granite in the area.Sr-Yb low value of the reaction zone and crustal thickening related granite.According to the petrological comparison,the corresponding rock types in this area are K-rich calcareous granites(KCG)and light-grained granites(MPG);the discussion of major elemental mapping results shows that the granites in this area are CCG type and POG type,R1 The R2 diagram shows that the tectonic setting is a transitional environment of late orogeneous and post-orogenic granites;trace element diagrams were cast in the intersection of Syn-COLG,volcanic arc(VAG)and intraplate environment(WPG).Formed by post-impact magmatic action.On the whole,granite Inner classes Jiashan area basic structure environment for the orogenic collision environment-extensional environment within the board postorogenic,mainly after collision environment,As for the cause of the stretching environment,it may be related to the Pacific plate activity.