Mountain building on top of a flipping subduction zone

Abstract:

The Taiwan orogeny in the framework of southeast Asian tectonics is of global importance, as subduction zone polarity reversals along the Eurasian margin occurred probably twice since in the Cenozoic. Additionally, due to oblique collision, and potential along strike variations of the passive margin its plate tectonic setting is exceptional, featuring transition of active subduction and ongoing collision at its southern termination and a more mature orogeny farther north. This allows for investigating the influence of the overriding plate on subduction dynamics, but also, vice versa, for understanding how subduction changed the overlying orogeny in three dimensions.

We present here a revised analysis of the plate tectonic framework of Southeast Asia since the Late Cretaceous, using global plate tectonic reconstructions focusing on the evolution of the Eurasian margin. In the Late Cretaceous, the morphology of the overriding Eurasian plate has been modified due to slab rollback of the Pacific Plate, which resulted in its thinning, back arc spreading, opening of the Proto South China Sea, and formation of extensional allochtons. When the young and buoyant Philippine Sea Plate reached the relatively older oceanic lithosphere of the Proto South China Sea, subduction polarity reversal along the Eurasian margin was triggered, which subsequently propagated northwards.

Polarity reversal along the margin was followed by the Taiwan orogeny, which involved accretion of an extensional allochton into the mountain belt. This, in combination with subduction reversal controls present day mountain building in Taiwan. Despite providing general insights on subduction dynamics, our results challenge the general view for the Taiwan orogen that it is possible to replace space and time, due to its plate tectonic configuration.