【摘要】 已有活动构造研究结果表明,天山北缘具有典型的大陆内部活动构造特征,表现为多排平行山体的背斜和逆断裂.为了研究乌鲁木齐坳陷区的地壳细结构、主要断裂展布和深、浅构造关系,2004年底,在乌鲁木齐西部的天山与准噶尔盆地之间的过渡带上,完成了一条近SN向的长度为78 km的深地震反射探测剖面.结果表明,该区地壳以双程走时9~10.5 s左右的强反射带为界分为上地壳和下地壳,上地壳厚约26~28 km,下地壳厚约23~25 km.双程走时5 s以上,反射层位丰富,构造形态清晰,且在剖面横向上具有明显不同的构造特征;在西山以南的区域,为一系列近东西向展布、南北向排列的逆冲背斜构造和一组自南向北逆冲的断裂,它们在深部均受到滑脱带的控制;在西山和王家沟一带,为一套向北陡倾的反射层系和一组沿层间滑动的断裂;剖面北部显示出了典型的沉积盆地图像,沉积盆地最深处约为10~12 km.双程走时6~9 s之间,为一些延续长度较短、反射能量较弱、且无规律可寻的凌乱反射,表明这部分地壳结构具有明显的"反射透明"性.Moho过渡带出现的时间位于双程走时14~17 s,对应壳幔过渡带厚度约为9~10 km.本区Moho面自北向南逐渐加深,剖面北部其深度约为50~52 km,在靠近北天山附近,其深度约为54~55 km.在剖面中部的西山附近,上、下地壳分界面反射和Moho过渡带反射变得模糊,且浅部地层还出现隆起和褶皱,推测与准噶尔盆地和天山的挤压过程有关.更多还原

【Abstract】 It is known from the active tectonic research results that the northern margin of Tianshan mountains is characterized with typical intra-continental active tectonics,which has thrust faults and anticlines with multiple parallel mountains.In order to investigate the fine crustal structures and the main fault geometries as well as the deep-shallow tectonic relations in rümqi depression,a deep seismic reflection profile of 78 km long,running in nearly SN direction,was completed in 2004.This profile is located in the transition zone between Tianshan mountains and Junggar Basin of the western rümqi.The results show that the crust beneath the investigated area is divided into upper and lower crusts by a strong reflective zone with about 9～10.5 s TWT.The thicknesses of the upper and lower crusts are about 26～28 km,23～25 km,respectively.There are rich reflective layers and clear tectonic patterns above 5s TWT while presenting obviously different tectonic features along the profile.In the southern region of Xishan,the stacked deep seismic reflection section has a series of thrust anticlines extending in the EW direction and arranging in the SN as well as a group of faults thrusting from south to north.All of those are influenced by the deep detachment zone.In the Xishan and Wangjiagou area,it shows a set of steeply north-dipping reflective layers and a group of faults slipping along the layers.The northern part of the profile shows the images of typical sediment basin and its deepest depth is about 10～12 km.Between 6 and 9 s TWT,the stacked deep seismic reflection section shows disordered reflections with comparatively short continuing time and weak energy.These indicate that this part of the crust is evidently possessed with "reflection transparence".The Moho transition zone occurs at 14～17 s TWT,and the zone thickness is about 9～10 km.In the studied area,the Moho discontinuity gradually deepens from north to south.Its depth is about 50～52 km at the northern segment of the profile and is about 54～55 km near north Tianshan.In the neighbourhood of Xishan at the middle profile,the reflections from the boundary between upper and lower crusts as well as Moho transition zone become misty while the shallow stratums show signs of uplift and fold,which may have something to do with the extrusions between Junggar basin and Tianshan mountains.更多还原