中文摘要：

在北大巴山推覆构造带前缘,北—北东倾斜的城口断裂和南—南西倾斜的高桥断裂形成一背冲式逆冲推覆体系,以两断层为界,其间为一巨型冲起构造。该冲起构造因边界断裂的产状特征、活动强度沿走向的差异,而表现出明显的分段性：其北西段为双向逆冲的＂正花状＂结构;而南东段为反向逆冲为主的＂半花状＂结构。同构造低温变质绢云母40Ar-39Ar年龄显示,城口断裂在燕山期（约143.3Ma）存在一次强烈的构造活动,导致北大巴构造带进一步逆冲扩展和强烈隆升。在逆冲-推覆向前扩展过程中,受锋缘外侧阻抗的影响,沿前缘部位形成一系列反向逆冲断层,从而形成巨型冲起构造。

英文摘要：

In the front of northern Dabashan thrust belt,there is a huge pop-up structure bounded by the N-NE-dipping Chengkou fault in the south,and the S-SW-dipping Gaoqiao fault in the north.The pop-up structure can be divided into several different segments along its strike,due to the variance of the occurrence characteristics and intensity of tectonic activity.To the northwest,it is a bidirectional thrusting structure and displays a positive flower structure;by contrast,the southeastern part is composed of a vertical Chengkou fault and a series of north-directed backthrusts,showing a semi-flower structure.The ^40Ar-^39Ar dating of syntectonic microthermal metamorphic sericite showed that Chengkou fault had an intense deformation during Yanshanian epoch （about 143.3 Ma）,causing rapid uplifting and thrusting of northern Dabashan thrust belt.During the propagation of this thrusting,a series of backthrusts formed because of the obstruction from the frontier of Dabashan thrust belt,and as a result,the pop-up structure was built up.