3D Geodynamic Models for HP‐UHP Rock Exhumation in Opposite‐Dip Double Subduction‐Collision Systems

Abstract

AbstractThe dynamics of high pressure (HP) and ultra‐high pressure (UHP) rock exhumation in opposite‐dip double subduction‐collision systems remain enigmatic. Here, we present 3D thermo‐mechanical numerical models to study the geodynamics of continental‐margin subduction, collision, and crustal exhumation of HP‐UHP metamorphic rocks in oppositely dipping adjacent subduction zones. In our model setups, an initial transform‐fault separates a purely oceanic subduction zone from an adjacent oceanic subduction zone that in time transforms into continental‐margin subduction. The results show that most simulations cause continental‐margin deep subduction within the collisional belts. In contrast to the results of 2D and 3D single subduction‐collision systems, the slab‐slab interactions strongly modify the down‐channel Couette flow and the up‐channel Poiseuille flow in the interplate region when the plate edges are close to each other. This prevents the exhumation of UHP metamorphic rocks to the Earth's surface. However, far from the interplate region, rapid exhumation of UHP rocks occurs in Alpine‐type models with a low Moho temperature, strong lower crust, and fast upper‐plate divergence, whereas the Taiwan‐type models occur for a high Moho temperature, weak lower crust, fast convergence, fast erosion, and are likely to facilitate rapid dome‐like HP exhumation. Based on our results, we suggest that the main characteristics, such as deep crustal subduction and rapid exhumation of HP‐UHP metamorphic rocks during mountain building in Taiwan (∼8 Ma to present) and in the Western Alps (∼49–35 Ma), may be the result of opposite‐dip double subduction‐collision systems.