Paleomagnetic study of Late Paleozoic rocks in the Tacheng Basin of West Junggar (NW China): Implications for the tectonic evolution of the western Altaids

To better understand the tectonic evolution of West Junggar in the western Altaids, we have conducted a combined paleomagnetic and geochronological study on Late Devonian (D-3), Late Carboniferous (C-2) and Early Permian (P-1) successions from the Tacheng Basin, northwest of China. Both primary and secondary characteristic remanent magnetization components have been successfully isolated and yield three reliable paleomagnetic poles of C-2 and Late Permian (P-2) ages. The C-2 and P-2 poles reveal a significant clockwise rotation of 35.6 degrees +/- 10.4 degrees which is comparable to the rotation deduced in the western part of the Chingiz Range during the time interval C-2 to P-2. Similar rotation patterns for the two units suggest that the Chingiz-West Junggar has remained as a quasi-rigid block by the Py time and constituted the northeast limb of the Kazakhstan Orodine. The differential rotation of ca. 25 degrees to 30 degrees deduced between the northeast and middle limbs of the Kazakhstan Orocline further suggests that at least a part of the curvature of the Balkhash Arc was acquired during the C-2 to P-2 interval and was a continuation of the middle Paleozoic oroclinal bending. Moreover, the C-2 poles for West Junggar and the Junggar Block are significantly different while the P-2 ones almost overlap supporting the view that final closure of the Balkhash-Junggar Ocean occurred during the C-2 to P-2 interval. On the other hand, a large-scale counterclockwise rotation of ca. 80 degrees to 90 degrees is observed in West Junggar and Junggar relative to the western part of the Chingiz Range since the Py time, and this rotation probably represents an important intracontinental deformation within the western part of the Altaids. A reconstruction of the Paleo-Asian Ocean has been proposed in which the Kazakhstan Orocline was emphasized by using the paleomagnetic results and geological evidence. (C) 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.