THE SIGNIFICANCE OF THE TECTONIC FACIES ANALYSIS BASED ON THE STUDY OF THE FOREL AND FOLD-THRUST BELT
Xiao Wenjiao1, Li Jiliang2, He Haiqing3
1. Institute of Geophysics, Chinese Academy of Sciences. Beijing 100101; 2. Institute of Geology, Chinese Academy of Sciences, Beijing 100029; 3. Institute of Geology, China Oil & Gas Corp., Beijing 100083
The NW Zhejiang was previously considered as "Caledonides" (Huang, 1980). Based on the discovery of the deep-water turbidites in the Upper Permian Dalong Fm. (P2d), and Changxing Fro. (P2c), and the Lower Triassic Zhengtang Fm. (T1z), the authors think that the NW Zhejiang is of SE-dipping passive continental margin from the Paleozoic to the Early Triassic. Together with the foreland molasse basin during the Late Triassic (T3w), the tectonics of the study area is characterized by a significant transition at some time between Early and Late Triassic period, when the study area experienced NW-ward deformation of folding and thursting. From SE to NW, the deformational style varies from multi-duplex, antiformal stack to hinterland-dipping duplex, and then to Jura Mountain-type fold zone with fold-style varying gradually from large-scale tight fold to mid-scale chevron fold, then to cylindrical fold. The zonation is shown as follows: 1) Northwest Zone; 2) Middle Zone; 3) Southeast Zone; 4) Chencai Zone. All the structural and sedimentary characteristics support the work hypothesis of Li jiliang (1989). By using the latest marine stratum involved in the deformation of the foreland fold and thrust belt and the oldest molasse basin as two significant constraints for the time of orogeny, the tectonic facies analysis provides a powerful tool for investigating tectonic evolution of orogenic belts.