Deep Seismic Reflection insights into the crustal structure and deformation characteristics of the Haiyuan Arcuate Fault Zone, NE Tibet

Abstract:

The Haiyuan triangular region in northeastern Tibet is located in the triple junction area of Tibet, Alxa block and Ordos block. Since the late Cenozoic, owing to the ongoing India-Eurasia collision, the NE Tibetan Plateau has been reactivated, resulting in initiation of a series of arcuate faults along the leading edge of the northeastern margin of Tibet. Previous studies on the collisional history between the Qilian and Alxa blocks in the early Paleozoic have provided great information for understanding deep structure of this region, and on the other hand, have indicated significant differences between the Haiyuan triangular region and Qilian Mountain to the west. Meanwhile, it is quite different from the Longmen Mountain area in tectonics, landform and petrology of eastern margin of Tibet. In this study, we carry out an integrated analysis on deep structure of the Haiyuan Arcuate tectonic zone with employment of a N-striking deep seismic reflection profile that cuts across NE Tibet and field data. With combination of geology and geophysics, we construct a crustal-scale architecture of the Haiyuan Arcuate tectonic zone. The obtained structure suggests that the Haiyuan Arcuate tectonic zone is located in the tectonic transitional zone of a back-arc basin accretionary complex belt, the northern Qilian orogenic belt, and the southern Alax bloc, where interactive magmatism in the early Paleozoic has additionally featured the special crust material in the Haiyuan triangular region. All these scenarios indicate the Haiyuan Arcuate tectonic zone is not stable and has potential to collapse when it reaches a certain elevation with the onset of northward compression from the Indian crust. Sinistral shearing on both sides was triggered as an accommodation.