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ABSTRACT: Ridges Subduction/Collision along the New Hebrides Island Arc

J. Daniel, J. Boultin, J. Y. Collot, J. P. Eissen, M. A. Fisher, H. G. Greene, S. Lallemand, M. Monzier, B. Pelletier

As a part of the SUBPSO project, organized jointly by IFREMER and ORSTOM, the SUBPSO I cruise was devoted to the study of both the collision between (1) the d'Entrecasteaux ridges and (2) the Loyalty ridge and the New Hebrides island arc. Eleven dives of the French submersible Nautile were conducted at depths from 1600 m to 5500 m.

Four dives were made along the flanks of Wousi Bank, the area where the North d'Entrecasteaux Ridge is colliding with the arc. Observations indicate that the deformation front is marked by a 1-2 m high scarp composed of slighty indurated mudstones. The lower arc slope has a very rough morphology undoubtedly produced by scouring from turbidity flows.

Three dives were made in the Bougainville zone, where the Bougainville guyot, a subducting guyot of the South d'Entrecasteaux chain, collides with the arc. Three cross sections were constructed across the arc slope in front of the guyot. The distribution of the deformation, occurring in deeper levels of the arc slope, suggests that during the subduction of the guyot, the interplate decollement apparently migrated upward in arc slope rocks to reach the top of the guyot.

Four dives were conducted over the collision zone "Loyalty ridge/New Hebrides arc." Near the trench, the Loyalty ridge has been sliced by normal faults along which the reef limestones, capping basaltic and rhyolitic breccias, collapsed at least 4000 m. Southwest verging anticlines, in an unusual position on the outer wall, 1000 m above the trench, were observed. These folds affect rocks of the lower part of the ridge flank.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990