乌鲁木齐山前坳陷逆断裂-褶皱带及其形成机制

REVERSE FAULT AND FOLD ZONE IN THE URUMQI RANGE FRONT DEPRESSION OF THE NORTHERN TIANSHAN AND ITS GENETIC MECHANISM

乌鲁木齐山前坳陷位于天山新生代再生造山带北侧，南以准噶尔南缘断裂与天山相隔，内部发育了几排逆断裂 背斜带，每一排构造带又由多个逆断裂 背斜组成。最南的齐古逆断裂 背斜带形成于中生代末，其北的玛纳斯逆断裂背斜带包含霍尔果斯、玛纳斯和吐谷鲁逆断裂背斜，形成于上新世末、早更新世初，受上、下２ 个滑脱面和断坡的控制，形成上、下２ 个背斜。再向北的独山子逆断裂背斜带由独山子、哈拉安德和安集海逆断裂背斜组成，形成于早、中更新世之间，主逆断裂向下在８ ～９ ｋｍ 深处的侏罗系中变为近水平滑脱面。此外，在独山子和吐谷鲁背斜的西北和东北还分别发育有正在形成之中的西湖和呼图壁隆起。研究了这些逆断裂 背斜带的地表和深部的构造特征、二维和三维几何学及运动学后指出，它们是在天山向准噶尔盆地扩展过程中发育于近水平滑脱面和不同断坡上的断展褶皱，独山子和安集海逆断裂 背斜的水平缩短量分别为２ ９００ ，１ ３５０ ｍ ，缩短速率分别为３９７ ，１８７ ｍ ｍ／ ａ。霍尔果斯、玛纳斯、吐谷鲁逆断裂 背斜的水平缩短量分别为５ ９００ ，６ ５００ ，６ ０００ ｍ ，相应的缩短速率分别为２０２，２２３ ，２０６ ｍ ｍ／ａ，准噶尔南缘断裂和乌鲁木齐山前坳陷第四纪?

The Tianshan is a late Cenozoic rejuvenated mountain belt in central Asia. The Urumqi range front depression is located along its northern margin. It consists of a series of reverse fault and folds that form a typical range front “thin skin' structure system. The southern Junggar fault separates the Tianshan from the Zhungarer depression to the north. Three rows of reverse fault and fold zones are present in the Urumqi depression. From south to north they are the Qigu, Manas, and Dushanzi active reverse fault and fold zones. The Qigu zone comprises several anticlines and was formed near the end of Mesozoic period. The authors′ studies indicate that the Qigu fold zone and the southern Junggar fault are no longer active since late Quaternary(about 30000 years ago). The Manas active reverse fault and fold zone consists of the Huoerguoes, Manas, and Tugulu reverse faults and anticlines. It was formed during the time from the end Pliocene to early Pleistocene period, and it is controlled by two décollements which are associated with two ramps and two anticlines. The lower décollement is located in the Jurassic sediment rocks about 8 to 9km below the surface. An anticline is developed on the top of the lower ramp. The upper décollement is located in the lower Tertiary rocks at the depth of about 3 to 4km. It merges downward into the lower décollement surface. The ramp and the anticline associated with the upper décollement crop out on the surface. The third row of the reverse fault and fold zone consists of the Dushanzi, Hala ande, and Anjihai reverse faults and anticlines, which were formed between the early and middle Pleistocene time. The Dushanzi anticline is more strongly deformed than the other two anticlines. The major reverse fault merges into the subhorizontal décollement surface in Jurassic rocks about 8 to 9km below the surface. In addition, the Xihu and the Hutubi uplifts are present in the north of the Dushanzi and the Tugulu anticlines respectively. These two uplifts become the north verging anticlines below the surface. But on the surface only slight uplift can be observed. The crustal shortening across these reverse fault and fold zones is calculated by means of the balanced cross section technique. The crustal shortening across the Dushanzi and the Anjihai reverse fault and anticline zones is 2900m and 1350m, and their rates are 3.97 and 1.87 mm/a respectively. The crustal shortening across the Huoerguoes, Manas, and Tugulu reverse fault and anticline zones is 5900, 6500, and 6000m with the shortening rates as 2.02, 2.23, and 2.06mm/a respectively. The above mentioned reverse fault and fold zones can be attributed to the fault propagation folds that grew from the Tianshan in the south toward the Junggar Basin in the north. Each of the reverse fault and fold zones is formed on the top of respective ramp up on the décollement several kilometers below the surface. The crustal shortening across the southern Zhungarer fault and the above mentioned reverse faults and folds indicates as 13.5 to 14.6km horizontally according to the balanced cross section calculation.