从反射地震剖面认识龙门山断裂带彭灌杂岩深部结构

Deep Structural Characteristics of Pengguan Complex in Longmenshan Fault Zone Derived from Seismic Reflective Profile

彭灌杂岩位于龙门山断裂带中段,是龙门山区域地质构造重要组成部分.通过对一条穿过彭灌杂岩中部的深地震反射剖面进行分析解释,描述该区域彭灌杂岩深部结构特征及形成机制.地震反射剖面分析表明彭灌杂岩在纵深上存在分层结构,且彭灌杂岩存在底界面,在该区域表现出无根特征,参考岩体层倾向推断原岩应来自现位置西北方向更深部;同时剖面能量图上映秀-北川深部断裂位置发育在彭灌杂岩体不同分层间隙,未破坏彭灌杂岩主岩体深部结构,彭灌杂岩体浅部的断层发育与龙门山地表断裂系统一致,表明彭灌杂岩成岩时间早于龙门山构造运动;综合岩性及成岩时间推断彭灌杂岩源于现有位置的西北方向大陆基底,由印支期板块运动中松潘陆块基底物质多期次上涌形成,并在喜山运动期受到西北方向应力推覆隆起到达目前位置.

Pengguan complex is located in the middle part of Longmenshan fault zone, which is an important part of Longmenshan regional tectonics. In this paper, the deep seismic reflection profile through the long axis of Pengguan complex is analyzed and interpreted, and the deep structural characteristics and formation mechanism of Pengguan complex are described. The analysis of seismic reflection profile shows that Pengguan complex is stratified in depth, with a bottom interface, and Pengguan complex shows rootless characteristics. Based on the analysis of its structural characteristics, it can be inferred that the in-situ rocks come from deeper and more western locations. The development of faults in the shallow part of Pengguan complex is consistent with the surface fault system of Longmenshan Mountain, which indicates that the diagenesis time of Pengguan complex is earlier than that of Longmenshan tectonic movement. At the same time, the Yingxiu-Beichuan fault in the deep part of the section energy map develops stratified gaps in different stages of Pengguan complex rock mass, which means it did not destroy the deep structure of Pengguan complex main rock mass. Referring to lithology and diagenetic time, it is inferred that Pengguan complex originated from the Songpan block basement material which was upwelled by compression during the Indosinian movement, the basement magma upwelled several times during the plate movement, and was uplifted by stress nappe in the northwest direction during the Himalayan movement to its present position.