Structural Deformation Responses In the Neoproterozoic Stratum to the Multiple Orogenesis Around the Southwestern Margin of the North China Craton

The structural deformations within the Neoproterozoic stratum along the southwestern margin of the North China Craton (NCC) offer a noteworthy illustration of the interactive relationship between structural deformation and orogenesis. Utilizing dating results from detrital zircons analyzed with U-Pb LA-ICP-MS and regional geological data, the sedimentary age of the epimetamorphic rocks, which outcrop in the southwestern margin of the Ordos Block, is constrained to the interval of 900-635 Ma. These rocks were deposited within a sedimentary basin encompassed by the Ordos Block, North Qinling orogenic belt, and Longshan structural belt. All three tectonic units contributed detritus, and the presence of interlayers of intraclast conglomerate suggests that the sedimentary setting experienced disturbance due to peripheral tectonic activities. Three episodes of structural deformation (D1, D2, and D3) are recognized in the epimetamorphic rocks. The D1 deformation is primarily characterized by parallel-bedding extensional deformation, likely induced by the opening of the Erlangping-Huluhe-Chenjiahe back-arc basin in the early stage of the Early Paleozoic. The D2 deformation is predominantly manifested as plastic compression deformation, likely induced by the closure of the Erlangping-Huluhe-Chenjiahe back-arc basin in the late stage of the Early Paleozoic. The D3 deformation is primarily characterized by a few parallel folds formed at the shallow-seated tectonic level under the compressional tectonic setting resulting from the closure of the Mianlue Ocean during the middle Triassic. It is suggested that the study area was located at the margin of the Ordos Block during the Mesoproterozoic, and the Longshan structural belt likely existed as an independent block at that time.