The northern New Hebrides back-arc troughs : history and relation with the North Fiji basin

1989

Article

Charvis Philippe, Pelletier Bernard

Tectonophysics, 1989, 170, p. 259-277

The New Hebrides back arc troughs (southwest Pacific) are located between the New Hebrides trench arc system and the active North Fiji marginal basin. They are restricted to the southern and northern segments of the arc and were generally related to effects of the Indo Australian subducting plate (rolling back and/or subduction of the d'Entrecasteaux ridge). A detailed bathymetric and magnetic survey over the northern back arc troughs is used to propose a new model for the origin of the New Hebrides back arc troughs. The northern troughs extend over a width of 60 km and are composed of N S trending grabens and horsts, discontinuous along strike and associated with volcanism. The troughs are disrupted southward at 13° 30'S, where the Hazel Holme fracture zone intercepts the New Hebrides island arc. The E W trending Hazel Holme fracture zone is an extensional feature bisecting the North Fiji basin. In its western end, the Hazel Hohne fracture zone is composed of a succession of horsts and grabens striking N90 ° N100 ° E. Geometrical and structural relationships between the back arc troughs and the Hazel Holme fracture zone suggest that both these extensional features result from the same process and are closely linked. The northern troughs western end of the Hazel Holme fracture zone region is dominated by N130° 135°E trending magnetic lineations typical of oceanic crust. These lineations are oblique to the horsts and grabens systems, and are characteristic of the old North Fiji basin oceanic crust. Consequently we conclude that the northern back arc troughs are partly developed on the North Fiji basin oceanic basement and that extensional tectonic processes postdate the oldest North Fiji basin oceanic crust. Morphological and structural evidence suggests that both the back arc troughs and the Hazel Holme fracture zone are recent, still active and result from NE SW extensional tectonics. Because other tectonic features throughout the North Fiji basin are related to the same stress field, it is inferred that such a NE SW extension could be a large scale deformation affecting the North Fiji basin. It is proposed that the back arc troughs are primarily related to this recent extension within the North Fiji basin, but their locations along the arc are also influenced by the subduction of the d'Entrecasteaux ridge which produces, south of 13°30'S, nearly E W trending compression and prevents the formation of troughs. Possibly, these recent extensional tectonic processes result from a major reorganization in the spreading process of the North Fiji basin, and could be as young as 0.6-0.7 Ma.

Géophysique marine [066GPHMAR]

TECTONIQUE DE PLAQUES ; STRUCTURE ; BATHYMETRIE ; RELIEF SOUS MARIN ; MAGNETISME ; ARC INSULAIRE ; FOSSE OCEANIQUE

PACIFIQUE TROPICAL OUEST ; VANUATU REGION ; FIDJI REGION

Fonds IRD [F B010017480] ; Montpellier (Centre IRD) ; Nouméa ;

fdi:010017480