Collisional model for rapid fore‐arc block rotations, arc curvature, and episodic back‐arc rifting in subduction settings

Abstract

We review geophysical and geological data from 23 active and ancient plate boundaries to document a compelling spatial and temporal relationship between collision, plate boundary curvature, rapid tectonic rotations, and the occurrence of back‐arc rifting. Our observations support a conceptual model where the change from subduction to collision causes rapid fore‐arc rotation (when viewed in a reference frame relative to the bounding tectonic plates), leading to marked plate boundary curvature. Our global compilation reveals that most active back‐arc rifts are associated with rapidly rotating fore arcs and nearby collisions. Thus, we propose that collision and rapid fore‐arc rotations play a major role in the evolution and kinematics of back‐arc basins. We conduct numerical modeling to better understand the physical processes behind these observed rapid tectonic rotations at convergent margins. Our results suggest that the presence of an indentor or choke point in the subduction system (e.g., collision) can generate rapid rotation of the fore arc about a nearby pole and lead to back‐arc rifting. The rate of fore‐arc rotation and back‐arc rifting depends on the incoming indentor velocity and can be greatly enhanced by slab rollback and the presence of a low‐viscosity back arc. Where viscosity of the back arc is low, fore‐arc rotation dominates; where back‐arc viscosity is high, the formation of strike‐slip faults and tectonic escape dominates. Our observational and model‐derived results illustrate that shallow crustal forces produced by the entry of buoyant features into subduction zones are a fundamental mechanism for the generation of fore‐arc block rotations, plate boundary curvature, back‐arc rift evolution, and tectonic escape in subduction systems. Rollback of the subducting slab within the mantle will certainly enhance the processes we describe but it is not the only driving force.