西准噶尔克拉玛依后山地区不同方向劈理特征及其动力学背景

Characteristics of Cleavages with Different Directions in Houshan Area of Karamay,Xinjiang,NW China and Their Geodynamic Background

劈理构造是一定应力场中形成的具有透入性的面状构造,一般代表变形过程中的最大压扁面.通过了解某一区域的劈理特征和发育序次,能对该区域的构造变形序次和大地构造演化研究有一定的指示意义.在准噶尔盆地西北缘扎伊尔山石炭纪地层中发育多组透入性的劈理构造,通过实地对研究区内劈理系统性地观察,理出了3类劈理:(1)早期与蛇绿混杂岩构造就位相关的劈理;(2)晚期顺达尔布特断裂和哈图断裂发育的断裂劈理以及(3)方位十分稳定,与层理发生不同程度置换,构成不同大小的夹角,代表近南北向区域性挤压运动的近EW向劈理.早期劈理产生于晚石炭世早晚之交,与研究区内蛇绿混杂岩系在晚石炭世陆块斜向汇拢洋盆汇聚闭合、蛇绿混杂岩陆续构造就位于上覆相对较新的地层系统有关;大型断裂劈理与区域内二叠-三叠纪大规模的北东-南西向断裂左旋走滑有关;东西向劈理切过305±15Ma的花岗斑岩脉,而未影响到不整合于石炭系地层之上的中生代地层(最老为晚三叠世),结合区域构造背景确定其形成时限为二叠纪末-早中三叠世,与第2类劈理近于准同时,可能与西伯利亚板块向南推挤导致的近南北向陆内挤压有关.

Cleavage is a type of penetrative planar rock feature produced under certain stress fields,commonly normal to the direction of maximum compression.Detailed investigation into the physical characteristics and sequences of different cleavages can facilitate the understanding of the regional deformational history,and further the tectonic evolution of a given area.Three categories of cleavages have been recognized through systematic observations of the penetrative cleavages developed in the Carboniferous turbidites in the Zaire Mountains of western Junggar：（1）relatively earlier cleavages associated with the tectonic emplacement of ophiolites;（2）later fault-related cleavages developed along major faults,such as the Darbut and Hatu faults;（3）cleavages with rather consistent east-west strike across region,and at various angles to bedding planes,which denote a widespread north-south regional compression.The earlier cleavages were formed during the Early-Late Late Carboniferous,when the older（Ordovician to Devonian）ophiolites got emplaced into the overlying younger（Carboniferous）strata due to the obliqueconvergence of different blocks and closing of ocean basins.The fault-related cleavages were related to extensive sinistral strike slip along NE-SW trending faults during the Permian-Triassic.The east-west cleavages didn＇t affect Mesozoic strata（the oldest of Late Triassic）in the region and crosscut granite porphyry veins dated as 305±15Ma.In the consideration of the extensional tectonic background of the area from the Late Carboniferous to Perimain,the east-west cleavages probably lasted from the latest Permian to Middle Triassic,roughly concurrent with the fault-related cleavages of the second type,both of which signify an intracontinental north-south compression concurred with the southward movement of the Siberian plate.