Speculations on the impact of catastrophic subduction initiation on the Earth System

Abstract

The physics of subduction initiation can be studied with numerical models of lithosphere dynamics, to the extent where we can now test the potential consequences of a catastrophic subduction initiation event on the Earth System. The South American Atlantic passive margin is here used to show that, once subduction has catastrophically initiated there, a major geodynamic reconfiguration of the South American plate (SAm) is likely to take place: (1) compression in the east will be inverted to extension, because ridge push will be replaced by subduction rollback and trench retreat; (2) compression in the west will be inverted to extension due to absolute rollback; and (3) without buttressing from the east and west, the Andes will collapse. Extension at both margins of continental SAm will produce two new volcanic arcs, several thousands of kilometres long each, bounded by trenches and two new back-arc basins. The spreading rate of the Mid-Atlantic Rift will significantly increase, because of the cumulative effect of ridge-push and slab-pull in the same direction. The substantially increased volcanism all around SAm and in the MAR will most likely release massive amounts of greenhouse and (toxic) gases into the atmosphere and oceans, which might lead to major oceanic and atmospheric circulation changes. We present new numerical modelling that supports the proposed evolution of the SAm after subduction has catastrophically initiated at its eastern passive margin.