Evolution of subduction dip angles and seismic stress patterns during arc-continent collision: Modeling Mindoro Island

Abstract

Here we dynamically model the temporal development of arc-continent collision, with particular attention to the evolution of slab dip angles and stress fields during approach to collisional locking (suturing). Our modeling is based on a simplified representation of Mindoro Island and the southern Manila Trench, which provide a natural laboratory in that convergence is ongoing to the north but collision is complete in the south, so that distance of 2D slices along the arc may serve as a reasonable proxy for time. We consider in detail the effects of the negative petrological buoyancy imparted to the slab upon encountering the thermally uplifted “410-km” (wadsleyite-forming) phase transition, as well as the effects of initial separation distance between the incoming Palawan continental fragment and the overriding Philippine Mobile Belt assemblage of arc-continent terranes. Despite simplifications in representing this tectonically complex region, our model reproduces important seismic observations, including the progressive steepening of slab dip and the growth of down-dip extensional stresses during the progress of collision. It also reveals that a significant contribution (of order 100 MPa) to the maximum attainable down-dip extensional stress arises from the negative petrological buoyancy of the uplifted “410-km” transition, and it illuminates how the initial separation of arc-continent fragments controls the temporal offset between collisional locking and the onset of negative petrological buoyancy. Finally, associated calculations of maximum shear stress may offer a partial explanation for the aseismic nature of tomographically proposed slab extensions below the Wadati-Benioff zone.