东海西湖凹陷平湖斜坡带裂陷期变换构造特征及其演化规律

The Characteristics of Tectonic Transform Evolutional Rules of Chasmic Cycles in Pinghu Slope of Xihu Depression of East China Sea

综合应用地震剖面解释结果和构造编图成果,对东海西湖凹陷平湖斜坡带区域构造变换带特征进行了系统地分析。研究区经历了3次裂陷,每个裂陷旋回期的变换构造带根据其对区域构造分段作用的规模可以分为3个级别,分别控制了相邻构造带间和构造带内的构造演化和构造线展布、构造样式与变形程度的差异。变换带的发育演化是动态的过程,与各裂陷时期构造活动的强弱具有很强的相关性:第一裂陷旋回时期,以主干断裂为主,发育规模较大,一级变换带具有明显的地势转换特征,以带间变换为主;第二裂陷旋回时期,受强烈拉张作用,三级变换带的数量和类型增多,各个构造单元内的构造组合型式更加复杂,部分一级变换带的类型也逐渐改变;第三裂陷旋回时期,伸展作用减弱,大部分断裂停止活动,三级变换带大量减少,大部分变换带的类型发生改变,构造单元间无明显区分性的特征。根据分段正断层的倾向及其组合特征,可将研究区局部的变换构造带分为转换斜坡型、斜向背斜型、地垒型3类,它们多是油气聚集的有利地区,对油气的勘探有指导意义。

The characteristics of the tectonic transform zones in the Pinghu slope of the western slope in Xihu Depression of East China Sea were analyzed systematically by comprehensively using the results of seismic profile interpretation and tectonic diagram.The studied area experienced three chasmic cycles.In different chasmic cycles,each tectonic transform zone of the chasmic cycles could be classified into three levels based its regional tectonic segment.They dominate the structural-sedimentary evolution,the expansion of structural lines,structural pattern and the difference of deformation extent between and inside the structural zones.Its growth evolution was closely related to the tectonic activity.During the first chasmic cycle,the main faults were dominated with a large scale of development,resulting in the obvious transition of geographic features in the first level transform structure and the transform was dominated between the zones.In the second chasmic cycle,the strong extension created many kinds and types of third level tectonic transform zones and the tectonic assemblages were more complex.Some of the first level transform structural zones were changed gradually.During the third chasmic cycle,with the extension was weakened,the most of faults stopped moving and the third tectonic zones were reduced at the large scale and the most of its types were changed without difference between the tectonic units.According to the attributes and consociation,the tectonic transform zones in the study area are classified into the transfer slope region,oblique anticlines and half graben.Most of them are favorable area for hydrocarbon accumulation.It provides a guidance for the exploration of oil and gas.