关键词: 浅层构造, 深部结构, 脆-韧转换带, 韧性剪切带, 玛纳斯地震区

Abstract: The Tianshan Mountains are a late Cenozoic rejuvenated mountain range in central Asia. The Urumqi Range front Depression is located along the northern margin of the Tianshan Mountains, consisting of a series of reverse fault-and-fold zones that form a typical thin skinned structural system. The southern Junggar Fault separates the Tianshan Mountains from the Urumqi Depression, in which three rows of reverse fault-and-fold zones are developed. From south to north, the three fault-and-fold zones are named Qigu reverse fault-and-fold zone, Manas reverse fault-and-fold zone and Dushanzi reverse fault-and-fold zone, respectively. Except for the anticlines in Qigu reverse fault-and-fold zone, the other anticlines in the Manas and Dushanzi reverse fault-and-fold zones are fault propagation fold. The shallow seismic exploration profiles show that the anticline consists of an overthrust fault zone, backward reverse fault and two partial anticlines. Four oil seismic exploration profiles show that the lower detachment fault exists in the Jurassic coal bearing strata, and the upper detachment fault exists in Paleogene strata. Some active folds are only formed on the ramps at the front of detachment fault. 2D electrical structure, deep seismic reflection profiling and crustal velocity structure across the northern Tianshan piedmont indicate that the active multilayered thrust tectonic system in the Urumqi Depression joins to a low-velocity(low resistance)layer through a brittle ductile transition zone in the crust of the Tianshan. The low-velocity layer in the upper crust of the Tianshan may be an active ductile shear zone. The brittle ductile transition zone under the Qigu reverse fault fold belt is the key link between the deep-seated active ductile shear zone and the shallow brittle fracture, and it is also the place of strong earthquake generation. The active surface structures in Manas earthquake region recorded only a part of the information of the activities of the deep-seated ductile shear zone.

Key words: shallow structure, deep structure, brittle ductile transition zone, ductile shear zone, Manas earthquake area