Zircon U-Pb Dating and Geochemistry of the Late Jurassic A-type Granite in Hadaengeer of Inner Mongolia and Its Tectonic Significance
Lying along the Solonker-Linxi collisional orogenic suture zone in Sonid Youqi of Inner Mongolia,the Hadaengeer A-type granite intruded into the Lower Permian Dashizhai Formation.LA-ICP-MS zircon U-Pb dating yielded a weighted average age of 151.9±0.7 Ma.The age suggests that the granite was emplaced in the Late Jurassic.The granite is geochemically characterized by high SiO2(71.36％～74.81％)and alkali(Na2O+K2O=8.12％～10.05％),but low CaO(0.71％～0.96％)and MgO(0.18％～0.28％).The obvious negative Eu anomaly(δEu=0.12～0.15),relative enrichment of Rb,Th,U,K and Ga,depletion of Ba,Sr,P and Ti,as well as high 10 000 Ga/Al(2.43～3.37),K2O/MgO(16.07～33.17),(Na2O+K2O)/CaO(8.45～12.56)values show the characteristics of A-type granite.According to the chemical subdivision diagrams of the A-type granitoids,the Hadaengeer A-type granite belongs to A2-type granitoid,which was formed and emplaced in a post-collisional extension setting.At the same time,in connection with the temperature and pressure conditions of magma origin,it shows that the pluton may be caused by the partial melting of hornblende rocks containing plagioclase in the crust under the condition of dehydration caused by the underplating of mantle derived basaltic magma caused by the separation of previously subducted plate fragments in the shallow low-pressure environment in the post orogenic stage.Furthermore,together with other A-type granites scattered in the eastern block of the Central Asian Orogenic Belt,the Hadaengeer A-type granite is recognized as the product of the post-orogenic extension of the Mongolian-Okhotsk tectonic domain in the Late Jurassic,which indicates the extensive middle-lower crust extension in the Middle-Late Jurassic.
A-type graniteLate Jurassicpost orogenic extensionSonid Youqi of Inner Mongolia
万方数据
维普
