Spatial and temporal distribution of the Carboniferous-Permian granitoids in northern Xinjiang and its adjacent areas,and its tectonic significance

Numerous granitoids occur in northern Xinjiang and its adjacent areas,with Carboniferous-Permian granitoids being most typical.This paper summarizes the spatial and temporal distribution characteristics of these granitoids.Carboniferous-Permian granitoids show different features in different units,and the peak values of their formation epochs are also different.Formation epochs of the Carboniferous-Permian granitoids in Altay are mainly concentrated in early Permian (289～266 Ma),and late Carboniferous seemed to be a distinct magmatic calm period.Western Junggar Carboniferous-Permian granitoids formation periods can be subdivided into early Carboniferous (340～320 Ma) and late Carboniferous-early Permian (310～290 Ma),with the latter being more stronger.Aluminum A-type granites,concentratedly formed at about 300 Ma,are widely spread,constituting an important feature of western Junggar.Carboniferous-Permian granitoids in eastern Junggar occur along the fault zones and were formed mainly from late Carboniferous to early Permian (320～270 Ma),characterized by the continuous emplacement of quite a number of alkaline (A-type) granites in this region in this period.Carboniferous-Permian granitoids in western Tianshan can be divided into three stages:early Carboniferous (355～345 Ma),late early Carboniferous-late Carboniferous (335～305 Ma) and early Permian (300～255 Ma).The early Permian granitic magma activity is the strongest,and Carboniferous granitoids mainly intruded into northern Tianshan,and the early Permian alkaline (A-type) granitoids are not only distributed in a large zonal area of southern Tianshan but also spread in northern Tianshan.Eastern Tianshan-Beishan is an area with most developed Carboniferous-Permian granitoids,characterized by both large quantities and wide distribution.Zircon ages show two obvious peaks,being respectively at 335～310 Ma and 300～270 Ma.Granitoids in eastern Tianshan are mostly Carboniferous ones,whereas granitoids in Beishan are mostly Carboniferous ones.In general,Carboniferous-Permian granitoids of northern Xinjiang and its adjacent areas were mainly formed in the late Carboniferous-early Permian period,especially during the early Permian,showing synchronization in the whole region.This period is also characterized by most developed alkaline (A-type) granitoids,which is regarded as the reflection of the extensional setting,maybe revealing extension characteristics in different tectonics.This is a microcosm of lots of acid and mafic-ultramafic magmatism in the Central Asian Orogenic Belt and the implication of its extensional setting.