Mantle avalanche as a driving force for tectonic reorganization in the southwest Pacific

The mechanism responsible for the recent, dramatic reorganization of the tectonic plate boundary in the New Hebrides region of the southwest Pacific has remained elusive. We propose that an ongoing avalanche of cold, dense slab material into the lower mantle, imaged by high-resolution seismic tomographic methods, provides the necessary driving force for this enigmatic evolution. Numerical experiments demonstrate that the avalanche model reconciles a broad suite of observational constraints, including the change in polarity of plate subduction, the rapid migration of the New Hebrides arc and opening of the North Fiji Basin, and the present-day geometry of slabs associated with both active and extinct subduction zones. (C) 2003 Elsevier Science B.V. All rights reserved.