Characteristics of Middle-Late Triassic Structural Deformation in Central Southwestern Fujian

The Middle-Late Triassic structural deformation in the southwestern Fujian province is the earliest record of the passive to active continental margin transformation of South China during the Early Mesozoic. However, this relatively short deformation process has not been studied in detail due to vegetation cover. We carried out LA-ICP-MS zircon U-Pb isotopic dating of the Weipu granite and its southeastern ‘dikes’ in the central part of Southwestern Fujian. The analytical results show that these granites, once considered to be formed in the Indosinian period, were formed at the end of the Early Paleozoic. Accordingly, the relationship between the granites and the overlying Upper Paleozoic different strata should be normal fault contact rather than the once believed intrusive contact. On this basis, we established the Mesozoic structural framework of the study area and identified three-stage deformation structures during the Middle and Late Triassic through field observations and structural analysis of the Upper Paleozoic strata on the southeast edge of the Weipu granite. From early to late, 1) NE-trending regional folds commonly associated with axial cleavages, 2) Top-to-SSW detachment faults, and 3) Top-to-E or -SE regional thrust. It reflects that the Early Mesozoic regional tectonic system experienced two transformations: from compression to extension to compression, which may be attributed to the combination of the far-field compression caused by arc-continent collision and the near-field extension induced by the upwelling of deep abnormal high heat flow. © 2023 Science Press. All rights reserved.