3D analogue modeling of the South China Sea: A discussion on breakup pattern

The opening of the South China Sea is one of the most important Cenozoic events in SE Asia. In order to investigate its tectonic evolution, three analogue modeling experiments were compared. The modeling results suggest that rifting pattern and orientation change of the rift zone were related to initial rheological stratification. Affected by the ductile flow of silicone (lower crust) and honey (asthenosphere), the faults became flattened, especially close to the breakup area. We conjecture that the slope area may bear relatively hotter and thinner lithosphere than the shelf area from the beginning of rifting due to stretching and mantle upwelling associated with this regional extension, which in turn lead to the change in initial rheological stratification and therefore the rifting pattern from shelf to slope. In the experiments, breakup developed first at isolated points, which grew and coalesced to become a single spreading area. The conjugate boundaries were either all concave or all convex. Where a rigid massif was located at the divergent boundary, stretching history was different. In this case, the northern and southern areas thinned rapidly and developed into two deep troughs, which may finally evolve into spreading centers. The shape of the massif controls the orientation and boundary shape of the spreading area. It is interpreted that crustal breakup was more viscous in style, and the NW sub sea basin developed along the northern trough of the Zhongsha-Xisha massif (Macclesfield Bank).