Multiphase Palaeogene-Miocene deformation history and regional implications of the Yinggehai Basin, offshore Ailao Shan-red river shear zone

In this paper, we investigate the structure of the Yinggehai Basin in the offshore Ailao Shan-Red River Shear Zone (ASRRSZ) to obtain a clear understanding of the basin's multiphase development from the Palaeogene to the Miocene, with links to regional tectonic events. The results of our work indicate that the initial rift architecture of the Yinggehai Basin was associated with extensional faults oriented NW-SE to NNW-SSE driven by a NE-SW- to ENE-WSW-trending extensional stress field, likely resulting from the far-field effect of the India-Eurasia collision. The formation of E-W-striking normal faults in the Palaeogene section and the strike-slip movement of pre-existing faults support the occurrence of sinistral strike-slip deformation during the second rifting stage to the early Miocene. In response to the left-lateral shearing of the ASRRSZ, which mostly ended in the early Miocene, flower-like structures, strike-slip faults and associated folds were detected in the northern and southern portions of the basin. Subsequently, middle to late Miocene compression produced a series of folds in the central basin. A series of layer-bound normal faults are present in the middle Miocene section suggesting a compactional or gravitationally driven origin. Although activity on the major faults in the main part of the basin almost ceased at the end of the early Miocene, a greater thickness of post-rift sediment was present inside the basin. This study suggests an extensional origin for the Yinggehai Basin and implies that both multiphase tectonic evolution and post-rift sediment loading played key roles in the Cenozoic development of this basin.