Spatial and Temporal Distribution of Granitoids in the Middle Segment of the Sino-Mongolian Border and Its Tectonic and Metallogenic Implications

Zircon U-Pb dating of the granitoids in the middle segment of the Sino-Mongolian border has yielded ages of 459-454Ma(Bainaimiao gneissic quartz diorite),268±6.9Ma(Daituojikashan miarolitic syenogranite of Xilin Hot),261.7±6.1 Ma(Baiyichagan hornblende biotite granodiorite of Xianghuang Banner),262.7±6.0 Ma(Xianghuang Banner monzogranite),277.2±2.9 Ma(Hadamiao biotite quartz diorite of Xianghuang Banner),231.1±7.6 Ma(Bayanxile syenogranite of Xilin Hot),216.9±5.4 Ma(Sonid Left Banner/Dongsu monzogranite) and 152.1±2.5 Ma(Shaertala alkali feldspar granite of Sonid Left Banner),respectively.Based on these ages and the chronological data already available,the authors hold that the granitoids have regular spatial and temporal distribution,i.e.,the granitoids were emplaced along three main belts and the intrusive epoch can be divided into five major stages,namely Early-Middle Paleozoic(490-387 Ma),Carboniferous(342-302 Ma),Permian(282-257 Ma),Triassic(249-204 Ma) and Late Mesozoic(152-118 Ma).There exist two giant alkaline granite belts in this area,i.e.,Permian alkaline granite belt near Dongwuzhumuqin and Late Triassic alkaline syenite belt along the northern margin of North China Craton,with magmtic activities being asymmetric.Regional geological,petrological and chronological evidence indicates that the Hegenshan ophiolite belt near the southern margin of the Siberian plate and Solonker-Xaro Morn ophiolite belt near the northern margin of Sino-Korean plate represent two oceans respectively.The Hegenshan Ocean was closed before middle Permian,and the Solonker-Xaro Morn Ocean(residual Paleo-Asian Ocean) was closed during the Late Permian-Early Triassic period,and the terminal collision between Sino-Korean and Siberian plates should have occurred at this time.Lots of granite-related mineral deposits have been found in this area,which include copper,tungsten,zinc and other deposits,produced mostly in the regional large-scale extensional setting of the post-orogenic or lithosphere delamination.