准噶尔盆地西北缘冲断构造新解  

A new insight into the thrust structures at the northwestern margin of Junggar Basin

作　　者：孟家峰[1,2] 郭召杰[1,2] 方世虎[3] 

机构地区：[1]造山带与地壳演化教育部重点实验室 [2]北京大学地球与空间科学学院,北京100871 [3]中国石油勘探开发研究院,北京100083

出　　处：《地学前缘》2009年第3期171-180,共10页Earth Science Frontiers

基　　金：国家油气重大专项(2008ZX05009-001)课题;国家重点基础研究发展计划"973"项目(2007CB411305)

摘　　要：准噶尔盆地西北缘最重要的构造特征是发育一组冲断构造。对这组冲断构造的冲断时限和冲断性质的认识不同,导致对准噶尔盆地的属性存在断陷盆地与前陆盆地之争。西北缘花岗岩及其中发育的岩墙群的精确年龄限定了研究区在314～255Ma中处于伸展状态。西北缘侏罗系沉积范围较三叠系广,早侏罗世发育碱性玄武岩,这些都表明准噶尔盆地在侏罗纪处于伸展阶段,盆地范围不断扩大。西北缘晚三叠世地层不整合覆盖于花岗岩之上,这种现象将本区冲断构造发生的时间限定为晚二叠世至早三叠世,最晚不超过晚三叠世。在地震资料解释的西北缘剖面上,冲断构造的前缘二叠纪地层平缓且厚度稳定。西北缘二叠系发育火山岩,沉积层序具从下到上粒度由粗变细的正旋回沉积特征,沉积速率稳定,沉降曲线由陡变缓,且古地温梯度和大地热流值均较高。西北缘的圈闭类型以岩性地层等非构造圈闭为主,以构造-岩性圈闭为辅。笔者认为西北缘冲断构造的性质是在314～255Ma伸展阶段与侏罗纪伸展阶段之间发育的一次短期反转构造,发育基底卷入的高角度冲断带,并非大规模与造山作用相关的前陆冲断带。The uppermost tectonic feature of the northwestern margin of Junggar Basin is a group of thrusts there. Disputes over these thrust structures are mainly about their formation time and attributes, and the relevant debate of whether the Junggar Basin is a faulted depression or a foreland basin. At the northwestern margin, jgranite and dyke swarms developed, suggesting that the studied area underwent an extension from 314 Ma to 255 Ma. The facts that the sedimentary scope of Jurassic is wider than that of Triassic and the alkali basalt developed in the early Jurassic indicate that the Junggar Basin underwent an extension and kept expansion in Jurassic. The late Triassic strata unconformably overlying the granite indicates that the formation time of these thrust structures might be from the late Permian to the early Triassic, no later than the Late Triassic. The seismic profile of northwestern margin shows gentle and stable Permian strata in thrust fronts. As to Permian sedimentation, its major characteristics include volcanic development, positive cycle fining up in the long term, higher depositional rate, a steep-to-gentle pattern of subsidence curve, as well as higher paleo-geothermal gradient and heat flow values. The main hydrocarbon traps are non-structural traps, like litho-stratigraphic traps, while the tectono-lithological traps are the minority. Based on the analysis above, we believe that the thrust structures are short term inversion structures occurring between 314-255 Ma extension and Jurassic extension, rather than large scale thrust belts associated with orogeny.

关 键 词：准噶尔盆地西北缘 二叠纪末到三叠纪 冲断构造 反转构造 

分 类 号：P542[天文地球—构造地质学]