Palaeozoic late collisional strike-slip deformations in Tianshan and Altay, Eastern Xinjiang, NW China

Abstract

In Central Asia, thrusts and shear zones resulting from Palaeozoic accretional events were reworked by E-W-trending ductile strike-slip faults during late Palaeozoic-early Mesozoic time. In the Tianshan range, microstructures and quartz C-axis fabrics show a main dextral shearing associated with sinistral localized shear zones. The relationship between these conjugate structures indicates a NNW-SSE-trending bulk shortening. In the Chinese Altay mountains, the existence of δ-type microstructures in an important sinistral mylonitic zone infers high rates of deformation. This shear zone is bordered by a late dextral ductile fault synchronous with a granite emplacement. Field evidence and datings from the literature provide chronological constraints. In the late Carboniferous, the sinistral mylonitic deformation took place in the Erqishi-Irtysh shear zone in the northeastern part of Xinjiang and in Kazakhstan. During the Early Permian, a regional dextral event occurred in the Tianshan range and under the whole of northern Xinjiang.