New Insights Into Phanerozoic Tectonics Of South China: Part 1, Polyphase Deformation In The Jiuling And Lianyunshan Domains Of The Central Jiangnan Orogen

摘要

The central Jiangnan Orogen, genetically formed by the Proterozoic Yangtze-Cathaysia collision, presents as a composite structural feature in the Phanerozoic with multiple ductile and brittle fabrics whose geometries, kinematics, and ages are crucial to decipher the tectonic evolution of south China. New structural observations coupled with thermochronological and geochronological studies of these fabrics document four main stages of deformation. The earliest stage in early Paleozoic time (460–420Ma) corresponds to combined E-trending dextral and northwest directed thrust shearing that was variably partitioned in anastomosing high-strain zones under greenschist-facies conditions (~400–500°C), related to the continued Yangtze-Cathaysia convergence externally driven by the suturing of south China with Australia. This event was heterogeneously overprinted by the second stage characterized by ~E-oriented folding in middle Triassic time, geodynamically resulting from the continental collision of south China with Indochina and North China. The third stage was locally developed by northwest and southeast vergent thrusts that truncated ~E-oriented folds in the Late Jurassic, due to northwestward subduction of the Paleo-Pacific plate. The latest stage involved normal faulting and tectonic unroofing in Cretaceous time, which resulted in basin opening and reset footwall 40Ar/39Ar ages in proximity to the Hengshan detachment fault, associated with roll-back of the subducting Paleo-Pacific plate.