天山北缘为典型的大陆内部活动构造特征，发育准噶尔盆地南缘逆冲带，主要表现为新生代时期形成的多排平行山体的背斜和逆冲断层。野外地质考察、地表填图指出，第二排背斜带玛纳斯背斜和吐谷鲁背斜核部均发育一条逆冲断层，背斜北翼发育一条逆冲断层，并导致河流阶地变形和断层崖的形成。地震资料解释和钻井数据证实玛纳斯背斜和吐谷鲁背斜北翼和核部存在多条向北逆冲的断层，在这些背斜和南侧第一排构造清水河背斜和奇古背斜之间的向斜之下存在隐伏的东湾背斜。二维地震测网构造解释指出东湾背斜为同时活动的、叠置的双重逆冲构造，并造成玛纳斯背斜和吐谷鲁背斜浅层发育一系列无序叠瓦逆冲断层。野外观察和地震解释的生长地层和地层不整合分析证实，这些无序逆冲断层形成时间主要为中新世晚期，一直到第四纪西域组（Q1 x）和乌苏群（Q2）时期和第四纪中晚期（Q4）。我们提出准南地区多个逆冲断层同期活动模式不同于新逆冲断层向前陆方向扩展时，旧断层不活动的模式。同期逆冲作用模式展示由于深部有序逆冲作用形成的双重逆冲构造发育期间，同期活动的逆冲作用可在浅层地表形成一系列无序逆冲断层，类似于叠瓦扇逆冲断层。%The Tian Shan is characteristic of typical intra-continent activities and hosts one thrusting zone in the southern margin of Junggar basin.The thrusting zone presents mainly as several rows of anticline and thrust fault which are parallel to trending of the maintains.Field investigation and mapping show that one thrust fault was developed within the core of the Manasi and Tugu anticlines and one thrust fault in the north wing of the anticline,both of which resulted in the formation of stream terrace deformation and fault escarpment.Drilling data,along with seismic data,show the existence of several north-trending thrusting faults in the Manasi anticline,and the north wing and core of the Tugu anticline,and of hidden Dongwan anticline beneath these faults and syncline between the Qingshuihe and Qigu anticlines.Interpretation of ETM remote data and 2D seismic data indicates that the Dongwan anticline was an active superimposed dural thrust structure,which resulted in a series of out-of-sequence thrusting imbricated faults developed shallowly in the Qinshuihe and the Qigu anticlines.The seismic interpretation for growth and stratum unconformity also suggests that the buried Dongwan anticline is a synchronous duplex and ‘out-of-sequence’ thrust fans was mainly formed from late Miocene to present. We follow the Boyer ’s synchronous thrust model to interpret the structural styles of the South Junggar thrust and fold belt which differs from a relatively simple hinterland-to-foreland (piggy-back)progression of thrusting,in which older thrusts were assumed to become deactivated as new thrusts propagated toward the foreland.The mode of synchronous thrusting indicates that during the development of dual thrust structure triggered by deep sequential thrusting,the synchronous thrusting in the subsurface can produce out-of-sequence thrusting at the surface,similar to imbricated thrust fault.
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