Mesozoic-Cenozoic structural deformation characteristics of Yuanling-Mayang basin and regional tectonic setting

Abstract: The Yuanling-Mayang basin is a giant Mesozoic continental basin in the middle segment of Xuefeng orogen. At present, the features of the Mesozoic-Cenozoic faults and folds in the basin is lack of systematic and deep research. The authors studied such aspects of this problem as Mesozoic-Cenozoic structural framework, characteristics of the faults and folds, deformation sequences and epochs and regional tectonic settings through tectonic profile and field geological investigation, and reached the following conclusions: (1) The principal tectonic framework of the Yuanling-Mayang basin is composed of NNE- to NE-trending normal faults, thrust faults and gentle folds, accompanied by other folds and faults of different trends and natures. In the western and middle basin, main deformations are normal faults which formed complex horst-graben structure, with weak fold deformation. On the east margin of the basin, controlled by the Huaihua-Yuanling fault belt, there occur strong deformations, such as thrust faults which mostly dip east and subordinately dip west, often accompanied by overturned tight folds. (2) The basin has undergone several tectonic events since Middle Triassic: ① Regional NW to NWW-striking compression in late Middle Triassic Indosinian movement which formed NE to NNE-trending folds and thrust faults. ② Regional NS-striking compression during Late Triassic-Early Jurassic which formed EW-trending folds and kinks. ③ Regional NWW to EW-striking compression in late Middle Jurassic Yanshanian movement which formed NS- and NNE-trending folds and thrust faults involving Upper Triassic and Lower-Middle Jurassic on the east margin of the basin. ④Regional NW-SE striking extension in Early Cretaceous which formed NE- to NNE-trending normal faults of different scales. ⑤ Regional NS-striking extension in Late Cretaceous which formed EW-trending normal fault. ⑥ Regional NE-striking compression during middle-late Paleogene which formed NW-trending folds and thrust faults, NEE- to NE-trending sinistral strike-slip faults, NNE-trending dextral strike-slip faults, and NEE- or NNE-trending conjugated shear joints involving Cretaceous and early layers. ⑦Regional NW compression during late Late Paleogene-Early Neogene which formed NE-trending folds, NE- to NNE-trending thrust faults and NS-trending thrust faults involving Cretaceous and early layers. Among them, the most important deformations are normal faults which originated from the NW-SE-striking extension in Early Cretaceous, the folds and thrust faults originated from the NW-striking compression during late Late Paleogene-Early Neogene. (3) The klippes located in the eastern basin and east periphery, defined by Previous researchers, such as Wangbinpo, Huangjin’ao, Tanwan and Mayang, do not exist. The so-called “klippes” are actually faulted blocks with deep roots, and the Banxi Group located in Paleozoic and Mesozoic were related to the movement of thrust faults or normal faults.