新疆塔里木库车冲断带东段更新世变形特征及其与西段的对比

PLEISTOCENE DEFORMATION FEATURES OF THE EAST SEGMENT,KUQA THRUST BELT IN TARIM,XINJIANG AND ITS COMPARISON WITH THE WEST SEGMENT

库车新生代前陆褶皱冲断带经历了两期重大的挤压变形事件:中新世晚期-上新世早期近东西向的逆冲活动及伴生的近北西向左行剪切变换带在全区有统一的变形样式;更新世变形使库车冲断带分为东、西两段。西段(西秋里塔格)山脉高耸,背斜及其核部冲断层延绵长逾百千米,仅见一条近北西向的左行剪切断层;东段发育一组近南北向的右行剪切断层,把东秋里塔格山脉切成若干段,东秋背斜的北翼断层、南翼断层和核部断层在每一段内都有自己的特点。更新世变形还造成冲断带东、西两段的地貌和水系有明显不同。作为油气藏盖层的膏盐层在其东、西两段有不同的层位和厚度,东段膏盐层的层位高且相对较薄,早期形成的油气藏经更新世变形改造后的保存情况逊于西段,据此讨论了东段油气勘探中应注意的问题。

The Cenozoic Kuqa foreland fold-and-thrust belt experienced two episodes of compressive deformation. The earlier one occurred in Late Miocene-Early Pliocene （sedimentary period of the Kangcun Formation ）, with the latitudinal thrusting and NW-strike shearing having a same deformation style in Kuqa area. The Pleistocene compressive deformation resulted in segmentation of the Kuqa thrust belt, which could be summarized as follows. 1 ） The gypsum-sah layers had varied stratohorizons and thicknesses in the west and east segments of the Kuqa belt. The reservoir traps formed in Late Miocene-Early Pliocene might be poorer preserved by the Pleistocene latitudinal thrusting in the Yiqikelike structural belt of the east segment,where the gypsum-sah layer was shallow-buried and thinner. 2） The Pleistocene anticlines and core thrusts well developed in the West Qiulitag of the west segment,and elongated more than 100km. The East Qiulitag anticline of the east segment was cut by a group of longitudinal faults,and became several sections. Correspondingly, the both had its own distinct geomorphies. 3 ） In the west segment, the transfer structure was NW-strike sinistral shear faults, and only one Pleistocene shear fault was found so far. While in the east segment the dominant transfer structure was longitudinal dextral shear fractures. Among them the Kuqa River fault acted in Late Miocene-Early Pliocene,and others occurred in Pleistocene. Owing to action of a group of longitudinal faults, the northern limb faults, southern limb faults and core faults of the East Qiulitag anticline had its own characters in each section. 4） The drainages had different features. In the west segment, the current was NW-direction,then turned towards east-by-northeast along the northern piedmont of the West Qiulitag Mountains. While in the east segment, a group of longitudinal rivers flowed through the East Qiulitag Mountains. Based on what mentioned above, the paper discussed, furthermore, some attentional problems of oil-gas exploration in the east segment in near future.