Rodriguez-Corcho, Andres1,2 Móron-Polanco, Sara1,2; Farrington, Rebecca1; Beucher, Romain3; Moresi, Louis; Montes3, Camilo4.
1The University of Melbourne, Melbourne, Parkville, Australia, 2The University of Sydney, Sydney, Camperdown, Australia, 3Australian National University, Canberra, Australia, 4Universidad del Norte, Barranquilla, Colombia
Arc-continent collision is the process by which intra-oceanic arc crust is accreted to continental margins. It is a process which commonly occurs in the tectonic-cycle and the most important mechanism that enables the growth of the continental crust since Phanerozoic times. We use numerical visco-plastic mechanical models to explore how compositional density contrasts and crustal-mantle dynamics control the formation of basins in continental margins during arc-continent collision. We performed a series of simulations only varying the thickness of the arc as it has been suggested to control the density profile (buoyancy) and rheology of intra-oceanic arcs and therefore the dynamics of collision. Modelling results show that arc-continent collision can evolve into two mechanisms: i) arc transference in dense arcs (15-31km in thickness), where the middle-lower arc crust is at least 2.1% denser than the adjacent continental crust-lithosphere; and ii) slab break-off in buoyant arcs (32-35 km in thickness), where the density contrast between the middle-lower intra-oceanic arc crust and the adjacent continental crust-lithosphere is lesser than the 2.1%. In turn, these two mechanisms trigger the partition of stress into extension in the continental margin and compression towards the subducting plate. We interpret that the partitioning in stress into compression and extension in all simulations is caused by a gravity-driven flow that equilibrates the contrasts in gravitational potential energy (GPE) stored in the lithosphere during arc-continent collision and episodes of lithospheric thickening. We argue that this gravity-driven flow applies a horizontal gravitational force directed from the collided arc towards the subducting plate (compressional) and the continental margin (extensional). This simultaneous occurrence of compression and extension in an active plate boundary allows the formation of basins in the continental margin without the need of the fore-arc or back-arc extension mechanisms. Finally, we conclude that the large-scale mantle return flow emerged from crustal-mantle dynamics (slab-anchoring) facilitates the stress partitioning by enhancing: i) compression and lithospheric thickening; and ii) the contrast in GPE between the accreted arc and the continental margin during collision.
Andres is a 3rd year PhD student at the University of Melbourne which research interests are the understanding of the evolution and dynamics of subduction zones and accretionary continental margins. Specifically, his research focus on the dynamics of arc-continent collision and how this process relates to basin formation