江汉盆地潜北断裂带分段差异活动及演化

潜北断裂带对沉积充填和油气差异富集具有控制作用，断裂带不同段的结构、构造差异性显著。早期关于潜北断裂带的地质认识及构造样式的解剖精度已不能满足当前精细化油气勘探的需求。因此，为了精细解析潜北断裂带的分段差异性及其成因演化，根据断层类型、几何学特征及成因演化，将潜北断裂带自西向东依次划分为6段，即新农段、钟市段、蚌湖段、潭口南段、潭口北段和三合场段。潜北断裂带不同段构造特征差异明显：新农段发育断阶构造和复合地堑；钟市段发育“荆沙红墙”和复杂断块；蚌湖段构造相对简单，发育同向断阶；潭口南段发育“座椅状”主断裂和复杂断块；潭口北段发育“躺椅状”主断裂和复杂断块；三合场段发育平缓斜坡及断阶、地堑—地垒构造。潜北断裂带分段差异活动受潜北地区多期、多方向不同性质区域应力所控制，且“荆沙红墙”、盐岩层、深部岩浆活动及先存构造等对断裂带分段差异活动也具有影响。断裂活动经历了四个构造演化阶段，即断陷期(沙市组—潜四下段沉积期)、断拗期(潜四上段—荆河镇组沉积期)、构造反转期(荆河镇组沉积末期—广华寺组沉积前)和拗陷及改造定型期(广华寺组—平原组沉积期)。该研究成果可为系统认识潜北断裂带分段差异活动机制及油气勘探实践提供理论参考。

Differential segmental activities of Qianbei fault zone in Jianghan Basin and its evolution

The Qianbei fault zone can control sedimentary filling and differential enrichment of oil and gas,and it demonstrates huge structural and tectonic differences in different segments. The previous geo-〖JP〗logical understanding of the Qianbei fault zone and the analysis accuracy of the tectonic style can no longer meet the needs of the current fine oil and gas exploration. Therefore,to finely analyze the segmental differences of the Qianbei fault zone and their cause evolution,this paper divides the Qianbei fault zone into six segments from the west to the east in accordance with the fault types,geometrical characteristics,and cause evolution,namely,Xinnong Segment,Zhongshi Segment,Banghu Segment,Tankounan Segment,Tankoubei Segment,and Sanhechang Segment. Significant differences in tectonic characteristics are identified in certain fault segments of the Qianbei fault zone:Fault terraces and compound grabens are developed in Xinnong Segment, and "Jingsha Red Walls" and complex fault blocks are developed in Zhongshi Segment; the structure in Banghu Segment is represented by synthetic fault terraces,which are relatively simple; armchair-shaped main faults and complex fault blocks are found in Tankounan Segment,and deck chair-shaped main faults and complex fault blocks are developed in Tankoubei Segment; Sanhechang Segment features a combination of gently-dipping slopes,fault terraces,and graben-horst structure. The differential segmental activities of the Qianbei fault zone are controlled by multi-phase and multi-directional regional stress with different properties,and "Jingsha Red Walls",salt layers, deep magmation,and pre-existing structures also exert a certain influence on those activities. The fault activities have experienced four stages of evolution,i.e.,the rift phase (the deposition period of Shashi Formation-lower 4th member of Qianjiang Formation),the fault-depression phase (the deposition period of the upper 4th member of Qianjiang Formation-Jinghezhen Formation),the structural inversion phase (the late deposition period of Jinghezhen Formation and pre-deposition period of Guanghuashi Formation),and the depression and reform-finalization phase (the deposition period of Guanghuashi Formation-Pingyuan Formation). The results can provide a theoretical reference for systematically understan-ding the differential segmental activity mechanism of the Qianbei fault zone and the practice of oil and gas exploration.