柴达木盆地西部阿拉尔断裂新生代构造变形特征及意义

Cenozoic tectonic deformation characteristics of Alar fault in southwestern Qaidam Basin and their significance

依据二维、三维地震资料,精细分析位于柴达木盆地西南部的阿拉尔断裂的几何学特征、水平缩短量及活动时间等,并探讨了其整个新生代的运动学特征、形成机制和油气地质意义。结果表明,阿拉尔断裂平面上可分为NWW走向的西段和近SN走向的东段,两段近于垂直;剖面上,其西段倾向南,倾角相对较小,而东段倾向西,断面近乎直立。阿拉尔断裂自新生代初期开始活动,西段以逆冲为主,水平缩短量和竖直抬升量均达到3 km以上,走滑量约为1 km;东段以右旋走滑为主,水平缩短量和竖直抬升量为1 km左右,走滑量达到3 km。阿拉尔断裂的形成和活动受南侧祁漫塔格造山带向北挤压和西侧阿尔金左旋走滑断裂的共同影响,柴西南地区断裂活动与油气形成具有良好的时空匹配关系,对形成油气藏具有重要意义。

Based on 2 D and 3 D seismic data,this study analyzes the geometric characteristics,horizontal shortening,and active time of the Alar fault in the southwestern Qaidam Basin in detail and explores the kinematic characteristics,formation mechanisms,and significance for hydrocarbon accumulation during the whole Cenozoic.The results are as follows.The Alar fault can be divided into the western segment in NWW trending and the eastern segment in nearly NS trending,which are nearly vertical.As shown in sections,the western segment inclines southward with a relatively small dip angle,while the eastern segment inclines westward with an almost vertical section.The Alar fault has been active since the Early Cenozoic.The activities of the western segment are dominated by thrust,with horizontal shortening and vertical uplift both exceeding 3 km and strike-slip motion for about 1 km.The activities in the eastern segment are dominated by dextral strike-slip motion,with horizontal shortening and vertical uplift of about 1 km and strike-slip motion of up to 3 km.The formation and activities of the Alar fault are jointly affected by the northward compression imposed by the Qimantage orogenic belt to the south and the Altun left-literal strike-slip fault to the west.There is a close spatial-temporal matching relationship between the fault activities and the formation of oil and gas in the southwestern Qaidam Basin.Therefore,the fault activities are of great significance for the formation of oil reservoirs.