Geochronological,Geochemical Characteristics And Tectonic Setting Of Mesozoic Granitic Rocks In Tuquan-Keerqinyouyizhongqi Region

This study elucidates the distribution range,characteristics,forming age,petrogenesis,magma source,and tectonic environment of the granitic rocks of Tuquan-Keerqinyouyizhongqi Region,based on the studies of field characteristics,petrology,petrography,LA-ICP-MS zircon U-Pb ages,and whole-rock major and trace element geochemistry.Then,the paper studied the petrogenesis and attributes of magma source of these samples.Finally,the paper divided several mesozoic magmatism and defines the tectonic setting of the granitic rocks of Tuquan-Keerqinyouyizhongqi region.In this study,several samples from four different area in this region were dated by the LA-ICP-MS technique,the tested result indicates that granodiorite of Mengentaolegai pluton was emplaced at 241±3Ma,the Bayanwula syenite was emplaced at 148±1Ma;the monzonitic granite of Baogetu pluton was emplaced at 226±1Ma and the granite porphyry of the Majiatun pluton was emplaced at 125±1Ma.Combining with previous and adjacent geological data,the authors differentiated magmatic activity into four periods which contains Middle Triassic,Late Triassic,Late Jurassic and Early Cretaceous.The study of mineral composition,characteristics of main trace elements,discriminating rock origin,covariation relationship and magmatic source area indicate that the Mengentaolegai granitoids are S-type granites,which are thickened by partial melting of the lower crust.The Baogetu granites are highly differentiated I-type granites,and their magmatic source regions are characterized by the mixing of crust and mantle;Bayanwuula granites are A₂ type granites,which are the products of partial melting of the subsurface shell material;The Majiatun granite porphyry are highly differentiated I-type granites which might generated from the partial melting of young crust material that has grown from depleted mantle.Combining with previous and adjacent geological data,we propose that the Middle Triassic S-type granites might indicate syn-collisional regional compressive background related to the closure of Paleo-Asian Ocean,while the Late Triassic I-type granites may be the product of post-oregenic lithospheric extension related to the closure of Paleo-Asian Ocean;However,The late Jurassic A₂ granites were mainly affected by the subduction and impact of the Pacific plate,and were fomed a transitional background from compression to extension.The Early Cretaceous I-type granites were formed from post-arc extensional tectonic setting caused by the withdraw of the Pacific plate subduction zone.