Geological And Geochemical Characteristics Of Early Cretaceous Granitophyre In Jianshan,Inner Mongolia

Jianshan in Inner Mongolia is located in the great hinggan mountains magmatic belt,which is the superposition of paleo-asian ocean tectonic domain and littoral Pacific tectonic domain.Jianshan granite porphyry is widely exposed and the degree of study is low.Based on the field geological characteristics,petrology,geochemistry and u-pb isotope of zircongrantie porphyry.The geological and geochemical characteristics of granite porphyry in jianshan area are summarized,and the petrogenesis and geotectonic background of jianshan area are discussed.Inner Mongolia Jianshan granite porphyry,exposed is widespread,mainly distributed in the study area in southwest Xiarigayinbudun,1028 highland,Hulegenhundi,the exposed area of about 7.99 km²,a rock wall and nodular north north east to zonal distribution,in Xiarigayinbudun mound region into the Early Cretaceous Epoch Baiyingaolao and upper Jurassic,Manketouebo,Manitu,on Hulugenhundi region into Jura,head of the Manketouebo.Most of the rocks are light flesh red granite porphyry,and the main mineral components are potassium feldspar(15?20%),plagioclase(5?10%),quartz(<10%)and a few dark minerals.According to petrology and geochemistry,Jianshan granite porphyry is characterized by high silicon(Si O₂ content of 69.73?77.65%),alkali rich(Na₂O+K₂O of7.40?8.13%),low magnesium and calcium.Trace and rare earth elements are characterized by enrichment of large ion lithophilic elements(LILE)Th and U,deficit of high-field strong elements such as Nb,Ta and Ti,with high Rb/Sr value.The total amount of rare earths is relatively high,the enriched type of light rare earths is relatively high,and Eu is negatively abnormal.The characteristics of rare earths indicate that the magma source area is A crust-source material.Based on the analysis of these chemical data,it is concluded that Jianshan granite porphyry belongs to a-type granite.According to the distinguishing diagram of tectonic environment,it can be judged that Jianshan granite porphyry was formed in post-orogenic extensional environment.According to the dating results of LA-ICP-MS zircon U-Pb,the granite porphyry in the study area was formed at 129.3±1.6Ma,indicating that the granite porphyry in Jianshan area was formed in the early cretaceous.