Abstract

The Alxa Block is a significant tectonic unit in the middle part of the southern Central Asian Orogenic Belt that was affected by multiple Paleozoic and Meso-Cenozoic deformation events. In this study, the results from detailed mapping and structural analysis coupled with new U-Pb zircon ages indicate that the northeastern Alxa Block has experienced ten deformation events since the late Paleozoic. Four separate structural domains are identified in the study area, and these domains contain intrusive and structural crosscutting relationships that allow the complex deformational history to be determined. Each deformation phase can be related to regional tectonic events associated with the consolidation of Central Asia's crust and subsequent intraplate reactivation. The first three events are tied to convergence between the Alxa Block, the North China and the Yangtze Cratons prior to and during closure of the Paleo-Asian Ocean in the Mid-Late Permian. Subsequently, sinistral displacement occurred between the Alxa Block and the North China Craton during the Triassic. Since the late Mesozoic, reactivation of the northeastern Alxa Block occurred repeatedly as an intraplate response to the subduction of the Paleo-Pacific Plate, the closure of the Mongol-Okhotsk Ocean, the collision between the Qiangtang and Lhasa blocks and the later collision between India and Eurasia. The Alxa Block provides a superb case study of how continental interior regions that evolve from plate boundaries to intraplate settings may remain susceptible to reactivation in different kinematic modes in response to distant plate margin-derived forces and internal gravitational forces that evolve through time.