Current tectonics of the Tonga New Hebrides region

This paper proposes a present-day tectonic map of the Tonga-New Hebrides re gion, the result of combining data from bathymetry, satellite-derived gravi ty, seismicity, magnetic measurements and GPS observations. Focal mechanism s and a large amount of bathymetric data collected during the last decade i n the Lau and North Fiji back-are basins indicate a deformation distributed over numerous spreading ridges rather than diffuse and shear-dominated as was previously thought. The region is also characterised by a large Variati on of both consumption rate along the arcs and opening rate along the back- are basins spreading centres. Geometry and rate of spreading in the Lau and North Fiji back-are basins, and segmentation of the Tonga and New Hebrides arcs, are closely related to, and significantly influenced by, the subduct ion of aseismic ridges, namely the Louisville, D'Entrecasteaux and Loyalty ridges. Where subducting aseismic ridges enter the trenches, we observe slo wer convergence, are-transverse strike-slip faulting, thrusting at the rear of arcs, and slow or absent back-are spreading. Rapid subduction correlate s with fast back-are opening. Sometimes parallel spreading ridges in the ba ck-are domain are required to accommodate the fast motion of convergence. ( C) 1998 Elsevier Science B.V. All rights reserved.