--> Large-Scale Retreat and Advance of Shallow Seas in Southeast Asia Driven by Mantle Flow

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Large-Scale Retreat and Advance of Shallow Seas in Southeast Asia Driven by Mantle Flow

Abstract

The basins of Southeast Asia have recorded a complex tectonic history from long-term convergence between the Eurasian, Tethyan, (proto-) Pacific and Australian plates. They host some of the world's most productive and prospective hydrocarbon resources. Almost half of Sundaland is presently submerged beneath a shallow sea, similar to the extent of flooding during the mid Cretaceous. However, most of Sundaland was emergent in the Late Cretaceous to Paleocene, resulting in widespread erosional environments and an enigmatic regional unconformity. We present new plate reconstructions of Southeast Asia for the post-Pangea timeframe using evolving plate topologies and modelled seafloor age-grids. We propose a model for the opening of the Proto South China Sea as a Late Cretaceous back-arc basin that detached a number of continental fragments from South China and transferred them to northern Borneo and the Philippine Archipelago. In addition, we present the first oroclinal bending model for Sundaland that reconciles paleomagnetic, geological and geophysical constraints of Borneo rotation, rifting in the Java Sea and the continuity of granitoid belts across the Tin Belt islands. Coupling this latest plate reconstruction developed in GPlates with simulations of global mantle flow in CitcomS, we demonstrate that a ~10–15 Myr hiatus in subduction along southern Sundaland in the Late Cretaceous, as a consequence of the accretion of the Woyla terranes and the east Java-West Sulawesi continental fragments to Sundaland, results in ~200 m of dynamic uplift by Eocene times. Renewed subduction along the Sunda Trench resulted in dynamic subsidence from ~30 Ma, leading to widespread long-term flooding of Sundaland even during rapid eustatic sea level falls, thus highlighting the strong control of dynamic topography in this region. However, the shift to regressive deltaic sedimentation in most Southeast Asian basins from ~15 Ma is likely a combination of the sea level falls and basin inversions resulting from the collision of the Australian margin with Sundaland. Our approach highlights the power of data-driven geodynamic simulations for understanding regional tectonic evolution and frontier hydrocarbon exploration.