Guadalupian (Permian) onset of subduction zone volcanism and geodynamic turnover from passive- to active-margin tectonics in southeast China

The subduction of the Pacific plate (including the paleo-Pacific plate) has a profound and extensive impact on the shaping and transformation of the South China plate and even the East Asian continent. The determination of the earliest start of subduction of the Pacific Plate is crucial to understanding the evolution and geodynamics of the Indosinian-aged and Yanshanian-aged tectonic events in the South China. For a long time, there has been controversy about the onset of the subduction of the Pacific Plate, mainly from the Jurassic and Permian views. One of the fundamental questions is that the Permian records of volcanism directly related to subduction has not been discovered so far in south China.

In a new paper by Zhang et al. (2020), published in the Geological Society of America Bulletin (https://doi.org/10.1130/B32014.1), Dr. ZHANG Feng-Qi, an Associated Professor of the Zhejiang University, reported the first systematic documentation of the occurrence of ash-fall tuff layers in the Permian depositional record in the Chaohu area, Anhui Province, eastern South China, and explained that the Guadalupian (270-264) ash-fall tuff layers in the late Paleozoic foreland basin archive represented the first subaerial volcanic products of this magmatic arc and signified a major geodynamic turnover from passive- to active-margin tectonics in SE Asia.

Figure 11. Paleogeographic evolution and tectonic setting of the South China block during Permian time (modified after Liu and Xü, 1994; Li and Li, 2007). (A) During the Cisuralian, all of South China was covered by shallow-marine carbonate, as part of the passive margin of the southeastern (present coordinates; same hereafter) coast. (B) Tectonic switch to an active margin along the eastern coast (X.H. Li et al., 2006), with widespread convergent margin volcanism and coastal uplift in eastern South China and distal ash-fall tuff deposited in the Gufeng Formation during the Guadalupian (identified Permian ash locations are after Xia et al., 1994; Sun et al., 2016; Huang et al., 2017; this study; Permian metamorphic rocks and their ages on Zhoushan Island are after Jiang et al., 2016). (C) During the Lopingian active continental margin of southeastern China and the inferred westward propagation of clastic deposition as a result of the migration of the accretionary orogeny along the coast of southeast China (detrital zircon sample locations and their youngest peak ages are after X.H. Li et al., 2012; Li et al., 2017; Zhong et al., 2013; Liang et al., 2013; Hu et al., 2015; this study). LIP—large igneous province.