Paleostress reconstruction of the Chaling-Yongxing basin in the central South China Block: Bulk (areal or multisite) vs. site stress tensors

A critical problem in fault-slip data stress analysis is separating the heterogeneous fault-slip data into homogeneous subsets. Recent attempts to solve this problem use tectonostratigraphic criteria based on the age of the sites where site stress tensors are calculated with a best-fit stress inversion method. The present study calculates bulk (areal or multisite) stress tensors from fault-slip data published in the Chaling-Yongxing Basin (CYB) in central South China with the Tensor Ratio Method (TRM). These tensors are compared with published site stress tensors to examine whether bulk or site stress tensors define regional or local stress regimes and similar or not paleostress history. Two regional stress regimes for the Late Cretaceous-Paleogene period, describing an older Late Cretaceous stage with transpression-strike-slip (TRP-SS) tectonics (NNE-SSW contraction and WNW-ESE extension) and a younger Paleogene stage with radial-pure (RE-PE) extensional tectonics (WNW-ESE extension), are defined. These stages are interpreted to be transitive through a transtension (TRN) tectonics of similar WNW-ESE extension and responsible for the formation and evolution of the CYB under tectonic processes related to the India-Asia collision and the retreat of the (Paleo)Pacific plate. The present analysis shows that tectonostratigraphic criteria based on the age of the exposed rocks might be insufficient for the coherent correlation of stress tensors resolved in sites of limited size and, thus, for unraveling the paleostress history of a region.