中上扬子区关键构造变革期、构造变形样式与油气保存

Key tectonic changes,deformation styles and hydrocarbon preservations in Middle-Upper Yangtze region

由于受不同的地球动力学背景和构造应力场控制,中、上扬子区在地史发展的各个阶段经历了多期的构造变革,形成了各种样式的断裂、褶皱和不整合构造,期间共经历了广西运动、印支运动、燕山运动和喜马拉雅运动等4期关键构造变革期。广西运动在研究区形成了大范围北东走向的构造变形;印支运动主要表现为海陆转换;燕山期为大型陆相湖盆沉积阶段;喜马拉雅期研究区遭受了来自3个方向的挤压。4期关键构造变革期对油气保存的影响主要表现为泥岩盖层的发育和保存。广西运动使中、上扬子区重要的志留系泥岩盖层大面积遭受破坏;中、下三叠统泥岩在印支运动遭受广泛剥蚀;燕山中期的构造运动对四川盆地以外早燕山期的区域盖层造成了严重的剥蚀;喜马拉雅运动使得隆起区上部的中、上中生界和新生界泥岩盖层完全破坏,仅在局部坳陷地区得以保存。除了泥岩盖层的发育以外,关键构造变革期的构造变形样式也制约了中、上扬子区的油气保存。川东地区主要以发育隔档式褶皱为主要特征,由紧闭背斜和宽缓向斜组成;湘鄂西地区的滑脱层较川东地区滑脱层深,主要为志留系和下寒武统泥岩;雪峰隆起由东南向西北的逆冲作用,使得其西北缘发育大量的地表高角度突破断层;在湘鄂西地区则发育低角度的逆冲断层,与下寒武统和志留系盖层形成了重要的油气保存条件。

Controlled by different geodynamic backgrounds and tectonic stress fields, the Middle-Upper Yangtze region had experienced stages of tectonic movements, resulting in styles of faults, folds and un- conformities. There were 4 key tectonic movements including the Guangxi, the Indosinian, the Yanshanian and the Himalayan. During the Guangxi Movement, large-scale NE-trending tectonic deformations were formed in the study area. The changes from marine to continent took place in the Indosinian Movement. Large terrestrial facies sedimentary was well developed during the Yanshanian period. The study area was extruded from 3 directions during the Himalayan period. The 4 key tectonic movements played important roles in development and preservation of mudstone cap formations. The Guangxi Movement made a large destruction of the Silurian mudstones which were important cap formations in the Middle-Upper Yangtze region. The Middle-Lower Triassic mudstones suffered extensive erosion during the Indosinian Movement. Tectonic movements during the middle Yanshanian period strongly destroyed the regional cap formations of the early Yanshanian period except for those in the Sichuan Basin. Due to the Himalayan Movement, the Middle-Upper Mesozoic and the Cenozoic mudstone cap formations in the uplift were completely destroyed, only preserved in some regional depressions. Besides the mudstone cap formations, tectonic deformation styles of the key tectonic movements also controlled hydrocarbon preservation in the study area. Chevron anticlines and relieved synclines were well developed in the east of Sichuan. Detachments in the west of Hunan and Hubei （mainly composed of the Silurian and the Lower Cambrian mudstones） were deeper than those in the east of Sichuan. The Xuefeng Uplift thrusted from SE to NW, resulting in large amounts of high-angle breakthroughs in the northwestern periphery. Meanwhile, in the west of Hunan and Hubei, low-angle thrusts matched with the Lower Cambrian and the Silurian cap formations, providing good conditions for hydrocarbon preservation.