Arc-arc collision in the Central Asian Orogenic Belt: insight from the eastern segment of the Irtysh Shear Zone, NW China.

As the largest accretionary orogen, the Central Asian Orogenic Belt (CAOB) involved episodic accretion/collision of arc terranes or microcontinental blocks from Neoproterozoic to late Paleozoic. Understanding the time and processes of such collisional events is crucial for the tectonic reconstruction of the CAOB. Here we focus on the Irtysh Shear Zone that represents the suture of the Peri-Siberian orogenic system (Chinese Altai Orogen) with the Kazakhstan orogenic system/East Junggar Terrane. On a basis of a combined structural and chronological study along the eastern segment of the Irtysh Shear Zone (Qinghe area), we reconstructed the collisional processes of the Chinese Altai Orogen with an intra-oceanic island arc of the East Junggar Terrane. Our results show that the oceanic basin between the Chinese Altai Orogen and the East Junggar Terrane was completely consumed in the late Carboniferous. The following arc-arc collision was characterized by early stage of orogen-perpendicular contraction, followed by orogen-parallel extension and transpressional deformation. The orogen-parallel extension, which is demonstrated by originally sub-horizontal foliation and associated orogen-parallel stretching lineation, may have be responsible for Permian high-temperature metamorphism and extensive magmatism in the southern Chinese Altai. On a scale of the western CAOB, the sinistral kinematics of the Irtysh Shear Zone, together with dextral shearing farther south in the Tianshan, suggests eastward tectonic wedging in the Permian, possibly in response to the coeval convergence of the Siberian, Baltic, and Tarim cratons.

E-mail addresses: pengfeili@gig.ac.cn, pengfeili2013@gmail.com (P. Li).

Acknowledgements: this study was financially supported by the National Natural Science Foundation of China (41872222), the National Key Research and Development Program of China (2017YFC0601205), Hong Kong Research Grant Council (HKU17302317) and a project from Guangdong Province (2019QN01H101).