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

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 oblique convergence 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±15 Ma. 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.