龙门山北段冲断前锋构造带特征

龙门山构造带北段大致从广元到安县一带,其冲断前锋构造带由北向南主要包括矿山梁、天井山、青林口和中坝等典型背斜构造。野外地质事实和地震剖面构造解释证实,龙门山北段前锋构造带中广泛发育了晚三叠世和新生代两期挤压构造变形,但在各背斜构造表现出不同变形特征。矿山梁和天井山构造表现为一个双重构造:浅层是一个晚三叠世形成的断层转折褶皱;深层则是新生代形成的多个逆冲岩片叠置所构成的隐伏堆垛背斜构造。青林口和中坝构造主体表现为叠瓦状逆冲,构造前锋是深部隐伏的断层转折褶皱和断层传播褶皱。从整体上看,龙门山北段冲断前锋构造带变形表现为上覆早期构造变形之下隐伏后期逆冲构造,从而形成双层结构。在龙门山北段前锋构造深部的隐伏冲断构造中可以进行油气勘探。

Characteristics of thrust structures in the northern Longmenshan front belt

The northern Longmenshan front belt extends along Guangyuan to Anxian and includes the typical anticlines such as Kuangshanliang, Tianjingshan, Qinglinkou and Zhongba. Field investigations and seismic interpretation ascertained two episode tectonic deformations in the Late Triassic and the Cenozoic periods in this front belt. The Kuangshanliang and Tianjingshan structures show a duplex comprising of a shallow fault-bend fold in the Late Triassic period and a deep buried stacking anticline imbricated by several thrust sheets in the Cenozoic period. The Qinglinkou and Zhongba structures show a imbricate structure in the Late Triassic and a buried fault bend fold and fault-propagation fold, which may be created or altered in the Cenozoic period. The front belt of the northern Longmenshan exhibits a double-layer structural style characterized by shallow thrust structures and deep buried ones. The buried thrust structures are the frontier fields for hydrocarbon exploration in the northern Longmenshan area.