Proto-South China Sea plate tectonics using subducted slab constraints from tomography
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The past size and location of the hypothesized proto-South China Sea vanished ocean basin has important plate-tectonic implications for southeast Asia since the Mesozoic. Here we present new details on proto-South China Sea paleogeography using mapped and unfolded slabs from tomography. Mapped slabs included: the Eurasia-South China Sea slab subducting at the Manila trench; the northern Philippine Sea plate slab subducting at the Ryukyu trench; and, a swath of detached, sub-horizontal, slab-like tomographic anomalies directly under the South China Sea at 450 to 700 km depths that we show is subducted ‘northern proto-South China Sea’ lithosphere. Slab unfolding revealed that the South China Sea lay directly above the ‘northern Proto-South China Sea’ with both extending 400 to 500 km to the east of the present Manila trench prior to subduction. Our slab-based plate reconstruction indicated the proto-South China Sea was consumed by double-sided subduction, as follows:  The ‘northern proto-South China Sea’ subducted in the Oligo-Miocene under the Dangerous Grounds and southward expanding South China Sea by in-place 'self subduction' similar to the western Mediterranean basins;  Limited southward subduction of the proto-South China Sea under Borneo occurred pre-Oligocene, represented by the 800-900 km deep 'southern Proto-South China Sea' slab.