Abstract
It is generally accepted that during the Mesozoic NE−NNE-trending folds overprinted E−W-trending folds to form the Longshan dome in the central South China continent, although the interference map does not tell the relative ages of the fold sets. In an effort to deepen our understanding of the process of reworking the continent, paleostress analysis using calcite twins was carried out in this study to verify or falsify this model. Ten limestone samples were collected from Upper-Paleozoic limestones on the flanks of the dome and were measured using the universal stage for calcite e-twins. E-twins in the samples are divisible into two kinds, thick (≥1 μm) and thin (<1 μm), indicative of relatively higher and lower deformation temperatures, respectively. Stress estimates obtained using the improved version of Shan et al.’s (2019) method were grouped into two layer-parallel shortening (LPS) subsets and three non-LPS subsets. These subsets comprise four tectonic regimes: NWW−SEE compression (LPS1 and non-LPS1), NNE−SSW compression (LPS2 and non-LPS2), NW−SE extension (non-LPS3a) and NNE−SSW extension (non-LPS3b). They were further arranged in a temperature-decreasing order to establish a complex deformation sequence of the study area. In the sequence NE−NNE-trending folds have an older age than E−W-trending folds, something different from the model. The approximately N−S regional compression responsible for the former folds should have a profound effect on the intensely deformed continent, something ignored in earlier work.
Highlights
IntroductionKilometer-scale superimposed folds are common in ancient accretionary [1,2,3,4] and collisional [5,6] orogens
By comparing the best estimates in the current and untilted states we classified them into two types: layer-parallel shortening (LPS) and non-layer-parallel shortening
The oval-shaped Longshan dome is located in the central portion of the South China continent
Summary
Kilometer-scale superimposed folds are common in ancient accretionary [1,2,3,4] and collisional [5,6] orogens They are generally diagnostic of a complex plate convergence and, of practical significance in understanding the deformation history of the orogens. They are not peculiar to the orogens, for example, the classic dome-basin structure or Ramsay’s [7] type 1 cross fold formed in the central portion of the South China continent (Figure 1a), when the continent had undergone intense deformation and intense magmatism during the Mesozoic [8,9,10,11,12,13]. This interference was caused by two fold sets: NE−NNE-trending tight folds and nearly E−W-trending open folds (Figure 1b)
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