MORPHOTECTONIC INDICATORS OF HOLOCENE FAULTING IN CENTRAL TIEN SHAN, KAZAKSTAN, AND GEODYNAMIC IMPLICATIONS

Abstract

The Holocene deformations of the central part of the Tien Shan mountain range in Kazakstan were studied in the field and by photointerpretation in order to reconstruct the geometry, kinematics and rate of faulting. The area is characterized by a complex pattern of widespread Holocene faults mainly striking ENE, E-W and ESE, in order of frequency, with left-lateral reverse, right-lateral reverse and reverse right-lateral motions, respectively. Each fault set has a bimodal dip with a high-angle inclination of motion planes. The calculated slip rate is 3–47 mm/a along the ENE striking faults, 3–28 mm/a along the ESE striking faults, and 1.5–3 mm/a on the E-W striking faults. The geodynamics of the area is consistent with a N-S directed shortening of the mountain belt, accompanied by an orogen-parallel escape mainly westward. This westward asymmetry is explained in terms of the structural heritage and presence of the Tarim Block which acts as an indenter to the SE of the study area.