Role of double-subduction dynamics in the topographic evolution of the Sunda Plate

Abstract

SUMMARY The Sunda Plate has shaped itself in a complex tectonic framework, driven by the interactions of multiple subduction zones in its history. Using thermomechanical computational fluid dynamic models we show in this paper how the in-dip double-subduction dynamics has controlled the first-order 3-D topography of this plate, currently bounded by two major N–S trending active trenches: Andaman–Sumatra–Java and Philippines on its western and eastern margins, respectively. We consider six E–W transects to account for an along-trench variation of the subduction parameters: subduction rate (Vc), shallow-depth (200–300 km) slab dip (α) and intertrench distance (ITD, λ) in our 2-D numerical experiments. The deviatoric stress fields and the topographic patterns are found to strongly depend on λ. For large ITDs (λ = 2000–3000 km), the overriding plate develops dominantly tensile stresses in its central zone, forming low topographic elevations. Decreasing λ results in a transition from extensional to contractional deformation, and promotes topographic uplift in the southern part. We explain these effects of λ in terms of the sublithospheric flow vortex patterns produced by the subducting slabs. Large λ (> 2000 km) generates non-interacting flow vortices, located close to the two trenches, leaving the mantle region beneath the overriding plate weakly perturbed. In contrast, small λ results in their strong interaction to produce a single upwelling zone, which facilitates the overriding plate to gain a higher topographic elevation. The stress field predicted from our model is validated with the observed stress patterns. We also interpolate a 3-D topographic surface and vertical uplift rates from the serial model sections, and compare them with the observed surface topography of the Sunda Plate.