塔里木巴楚隆起北缘吐木休克楔形基底卷入构造

A Large-scale Basement-involved Wedge Structure of Tumuxiuke Fault in Northern Margin of Bachu Uplift in the Tarim Basin, Northwest China

石油地震资料揭示出塔里木盆地中央巴楚隆起为结晶基底和古生代地层相对隆升区,多数地区缺失中新生界,顶部为第四系陆相碎屑岩不整合覆盖隐伏隆起。在隆起南北两侧构造变形比较强烈,均发育基底卷入的逆冲构造和古生界内逆冲构造。运用断层相关褶皱理论,通过对研究区的二维地震测网解释及钻井标定,综合研究得出巴楚隆起北侧吐木休克卷入基底逆冲断层倾向南,向北逆冲,前寒武系基底到早古生代地层被错断。新生代时期的生长地层特征指示基底卷入构造于古近纪、中新世-上新世和更新世均有活动。构造分析表明基底卷入构造于中生代末期还有一次活动,说明吐木休克构造由多期构造运动形成。向北逆冲的吐木休克基底断层和盖层褶皱构造的向南反冲逆冲断层或滑脱断层共同组成基底卷入楔形构造,楔形点同时位于基底和盖层中。盖层构造以中寒武统膏岩为滑动面,向南逆冲,发育断层扩展或滑脱背斜构造。基底断层和盖层滑脱断层在剖面上组成典型的楔形构造几何形态,平面上形成三角形构造。地震剖面综合解释成果图显示,吐木休克弧形逆冲构造东部盖层反冲构造,即基底卷入楔形构造表现较为清楚,向西则表现不太明显,但地震反射波组(地层转折)指示盖层中仍存在这些反冲构造。纵向地震剖面和联络地震剖面均显示出存在该类构造。吐木休克基底卷入断层弧形构造顶部位移最大,盖层变形相对最小;向东西两侧基底断层位移逐渐减小,盖层构造位移相应逐渐增加。研究认为,塔里木巴楚隆起系挤压作用下,刚性地壳发生挠曲而形成的变形区带。

Seismic data show that the crust at the Bachu buried uplift in the central Tarim consists of the crystallinebasement and Paleozoic strata overlain by the Quaternary terrestrial clastic rocks.Both north and south margins of theBachu uplift have intense deformation with basement-involved structures and thrust fault in the Paleozoic cover.Alarge-scale northward actuate structure of the Tumuxiuke basement-involved fault is developed in the north margin ofthe Bachu Uplift.Using the fault-related theories,we have interpreted2D seismic lines which revealed the Tumuxiukefault is a basement-involved fault that dips to south with the Precambrian and Paleozoic strata thrusted northward.Tectonic analysis indicates that the Tumuxiuke thrust belt was initiated in the Late Mesozoic.The Cenzoic growth stratashows that the Tumuxiuke thrust belt was reactivated in the Paleocene,Miocene?Pliocene and Pleistocene,and formedby multi-period tectonic movement.The Tumuxiuke thrust belt is composed of a northward thrust basement-involvedfault and a detachment fold in the Cambrian or fault-propagation fold in the cover.The thrust belt is a wedged-shapedbasement-involved structure with the wedged points located in both the basement and the cover,a triangle-shapedstructure in plane view.The seismic data show that the wedge-shaped basement-involved structure is obvious in the eastpart,ambiguous in the west part and central part of the arcuate Tumuxiuke thrust belt.In addition,back-thrust issupported by the analysis of axial surfaces of the seismic reflection sequences.We suggest that both the longitudinal andtransverse seismic lines exhibit same geometries.The displacement in the arc-shaped top of the Tumuxiukebasement-involved fault is largest,while the displacement decreases toward east and west ends and within the cover.Basement-involved structures(or thick-skinned structures)are generally developed in fore-bulge of the foreland basin orthe trailing edges of the foreland thrust-fold belt.Basement-involved structure in the forebulge of the foreland basin mayresult from foreland thrust-fold belt absorbing of horizontal shortening of an orogenic belt.Our results show that theBachu uplift in the central Tarim is a deformational belt that formed through buckling of rigid Tarim crust due to acompressional deformation corresponding to the Indian?Eurasia collision during the Cenozoic.