Geodynamics of Sundaland since the Eocene

Abstract:

Sundaland is the continental core of southeast Asia bounded by subduction zones since early Mesozoic. Many Sundaland basins, extensional in origin, have formed since Late Eocene. These rift basins experienced extensive inversion since early Miocene. The basins and the adjacent continental crust subsided with a regional sea level rise during a period of basin inversion and falling global sea level, suggesting control beyond eustasy and lithospheric deformation. The mechanism of this large-scale synchronous inversion and subsidence is not well understood. We use four dimensional dynamic models that explicitly assimilate the plate tectonic history and additional geological and geophysical data to investigate the underlying causes for the enigmatic evolution of Cenozoic Sundaland basins. The assimilation method honors both empirical data at the surface (including the seafloor age, plate motion velocity, subduction history) and mantle dynamics at depth and predicts mantle structure, surface topography and intraplate stress. These later expressions are compared against independent observations. With continuously closing plates, we embed deforming plates into the conventional rigid plate models in GPlates, thus enabling us to model continental deformation and mantle dynamics jointly. Models are initiated in the early Eocene with the temperature field derived from the backward integration of the present temperature field synthesized from seismic models. The velocity-temperature perturbation scaling ratio and depth and temperature dependent viscosity are derived by fitting the geoid. Our models are consistent with a slab avalanche occurring beneath Sundaland in the early Miocene. The slab avalanche induced large scale subsidence and compression across the southern Sundaland region, which correspond to the synchronous marine inundation and basin inversion since early to middle Miocene regionally. The model results suggest that the evolution of Sundaland basins is dominated by both surface lithospheric deformation and deep mantle dynamics.