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本文依据断层相关褶皱几何学原理,对龙门山中段地震剖面进行了精细解释。研究发现,龙门山中段山前带浅层冲断系统存在多套滑脱层,具有上下分层变形特征。浅层滑脱层为上三叠统须家河组三段(T_3~x3)的碳质页岩夹煤层,其上发育双重构造和叠瓦构造;下三叠统嘉陵江组四、五段(T_1j~(4-5))的膏岩层,发育断层传播褶皱、冲起构造和构造楔;深层为下寒武统的泥页岩层,发育断层转折褶皱和滑脱褶皱。该区滑脱断层所控制的地层变形和缩短量各不相同,其中三叠系上统缩短量最大,大于30 km;三叠系下统至古生界地层缩短量约为14.5 km;侏罗系以上的地层缩短量则较小。研究区内的通济场断裂(F_3)为印支末期形成的一套逆冲断层组,其下部交于下寒武统滑脱层,深度约为10 km;关口断层(F_4)和彭县断裂(F_5)为晚侏罗世一早白垩世形成的逆冲断层,下部交与下三叠统嘉陵江组滑脱层,深度大约为8～10 km。这些断层以前展的方式破裂,并且长期活动。龙门山中段自中生代以来存在多期构造事件,主要发生诺利末期、印支晚幕、燕山期和喜马拉雅期。其中,燕山期和喜马拉雅期是龙门山活动最强烈的两个阶段,在龙门山中段山前带表现为大量断裂的长期活动,地壳缩短和龙门山快速隆升,并形成多种构造样式。
Based on the theory of fault-related fold geometry, this paper gives a detailed explanation of the seismic section in the middle part of Longmenshan. It is found that there are several sets of slip-off layers in the shallow-thrust system in the foreland belt of the middle Longmen Mountains, with the characteristics of upper and lower delamination delamination. The shallow skidding layer is a carbonaceous shale interbed in the third member of the Upper Triassic Xujiahe Formation (T_3 ~ x3), with dual structure and imbricate structure developed on the upper Triassic Xujiahe Formation. ~ (4-5)) gypsum strata, the development of fault propagation folds, uplift tectonic and structural wedge; deep shale layer of the Lower Cambrian, the development of fault fold folds and slip folds. The deformation and shortening of the strata controlled by the detachment fault are different in this area, of which the shortening of the Triassic system is the largest, more than 30 km, the shortening of the Triassic Lower Paleozoic strata is about 14.5 km, the Jurassic Above the strata to shorten the amount of smaller. The Tongji fault (F_3) in the study area is a set of thrust faults formed in the last Indosinian period, the lower part of which is intersected by the Lower Cambrian slip detachment and has a depth of about 10 km. The main fault (F_4) and Pengxian fault (F_5) is a thrust fault formed during the Late Jurassic and Early Cretaceous, and the lower part of the fault is connected with the Lower Triassic Jialingjiang Formation. The depth is about 8 ~ 10 km. These faults ruptured in the way they were before and long-term activities. Since the Mesozoic, there are multiple tectonic events occurring in the middle of the Longmenshan section, mainly occurring in the Noli end, the Indosinian, the Yanshanian and the Himalayan. Among them, the Yanshanian and Himalayan periods are the two most intense phases of the Longmenshan. Long-range activities of massive fractures in the middle Longmenshan show that the crust is shortened and the Longmen Mountains are rapidly uplifted, forming various tectonic styles.