太行山东缘石家庄南部地壳结构及断裂活动性探测

Survey of crustal structure and fault activity around southern Shijiazhuang in the eastern margins of Taihangshan Mts

采用深、浅地震反射和钻孔地质剖面相结合的方法,对太行山东缘石家庄南部的地壳结构和隐伏断裂的活动性进行了研究.深地震反射探测结果表明,该区地壳厚度33～38km,莫霍面从华北平原向太行山下倾伏.石家庄—晋县凹陷是受拆离断层控制的盆岭构造,太行山山前断裂为凹陷的西边界断裂,表现为上陡下缓的铲形断裂.石家庄—晋县凹陷中还发育北席断裂和栾城断裂,它们与太行山山前断裂一样受拆离断层的控制,未错断早更新世晚期以来沉积的地层不属于活动断裂.深地震反射剖面的中部还揭示了一个近垂直的穹窿状反射异常体,它可能起源于莫霍面,向上,穿过上、下地壳分界面,并延伸至上地壳.穹窿状反射异常体内部反射波视频率随深度增加而降低,在莫霍面附近的壳幔过渡带也出现明显的频率降低、界面扭曲和变形现象,推断它可能是上地幔岩浆上涌到地壳内部的侵入体.结合电磁测深结果可以发现,上地幔热物质的上涌和东、西向拉张可能是形成石家庄—晋县凹陷的动力学机制.探测结果为深入理解石家庄地区的深部地球动力学过程、华北克拉通破坏机制、深浅构造关系和地震构造提供了依据.

We used the method combining deep and shallow seismic reflection to explore the fine crustal structure and buried faults in the Shijiazhuang segment along the Taihangshan piedmont fault zone.Deep seismic reflection results show that the crust is 33~38km thick,and the Moho plunges from under the north China plain to the Taihangshan Mts.The Shijiazhuang-Jinxiandepression is a basin-ridge structure controlled by a detachment fault.The west boundary fault of the Shijiazhuang-Jinxian depression is the eastern piedmont fault of the Taihang Mts that is characterized by a listric fault.The Beixi fault and Luancheng fault are also in the ShijiazhuangJinxian depression,this two faults like the eastern piedmont fault of Taihang Mts is controlled by the detachment fault.Eastern piedmont fault of Taihang Mts,Beixi fault and Luancheng fault,both do not cut the late-period sedimentary formation of early Pleistocene,thus are not active faults.The middle part of deep seismic reflection profile also reveals a reflective abnormal body that is of a nearly vertical dome shape.This abnormal body may be originated from the Moho,cutting the interface of upper-lower crust upward,and entering the upper crust.The internal reflection wave frequency in the abnormal body decreases with increasing depth.Nearby the Moho,the reflection waves were distorted and deformed obviously,suggesting that upper mantle magma intruded into crust.Combined with broadband magnetelluric（MT）survey results,we also find that the upwelling of hot material from upper mantle,the east-west directed tension may be form the dynamics mechanism of the Shijiazhuang-Jinxian depression.Our survey results provide a basis for understanding the deep geodynamic process,the north China craton destruction mechanism,deep-shallow structure relations and seismotectonics of the Shijiazhuang area.