麻江地区节理发育特征及对应力场转换的指示

Joint development features and their functions as indicators for stress field transformation in the Majiang area

贵州麻江地区发育的麻江古油藏是我国南方海相残留单元中特大型古油藏之一。该地区受多期构造运动的影响,具有复杂的构造演化过程,岩层中发育大量节理。节理是地表岩石经历多期构造演化和多期构造应力场作用下的最终表现,而它作为应力场特征的敏感示踪标志,可用来恢复应力场的状态及其演化(转换)过程。通过对麻江地区不同地层中节理的实地测量,统计分析了节理性质、产状以及几何样式等;依据节理交切关系及其与断层的切割关系,并结合区域地质背景,认为麻江地区主要发育五期节理,由老到新依次为NEE-SE向早期平面X型共轭剪节理、SEE-NNE向X型共轭剪节理、NE向节理、SSE向节理和近EW向节理。这五期节理分别是都匀运动、广西运动早期、广西运动晚期、印支运动和燕山运动的产物。最后依据节理产状要素反演了每期构造应力场,计算结果表明麻江地区主压应力场依次发生了SEE—SE—SSE—EW的顺时针方向的转换。

The Majiang paleo-reservoir of hydrocarbon formed in the Majiang area, Guizhou Province, is one of the large-scale paleo-reservoirs in the residual units of marine strata in southern China. Affected by multi-stages of tectonic movements and experiencing complicated tectonic evolution processes, a large amount of joints were developed in the strata in the area. Joints are the final representation of surface rocks being reshaped and reformed by multi-stages of tectonic evolution and stress fields, and can be used to reconstruct stress status and evolution（transformation） processes as indicators for tracing the stress fields. Actual measurements of joints in different strata in the Majiang area are gathered for a statistical analysis on characteristics, occurrence, and geometries of the joints. The regional geological background as well as the intersecting relationship of joints and their crosscutting relationship with faults indicate that there are five stages of joints developed in the Majiang area.They are, from the oldest to the youngest, the planar X-shaped conjugated shear joints of early conjugated shear joints of SEE-NNE orientation, joints of NE, SSE, and near EW orientations stage, X-shaped , which are the products of the Duyun Movement, early Guangxi Movement, Indo-China Movement, and Yanshang Movement respectively. The tectonic stress field calculation shows that the principle of each stage is reconstructed through inversion with joint occurrence. The stress field in the Majiang area had shifted clockwise from SEE to SE,SSE, and finally EW.