Marginal basins of the SW Pacific and the preservation and recognition of their ancient analogues: a review

Abstract

Summary Marginal basins of the SW Pacific floored by oceanic lithosphere comprise those formed by sea-floor spreading immediately behind active magmatic arcs (back-arc basins) and those created by the rifting of continental crust without obvious connection to an arc system (small ocean basins). The basins opened rapidly, range greatly in shape and size, and show diverse relations to sediment sources. Thick sediment piles mainly accumulated adjacent to emergent continental margins or active arcs, with thin sequences of pelagic sediments, ash, and fine grained turbidites on basin floors. Facies are commonly asymmetrically distributed. Basaltic magmatic activity, mild deformation and submarine erosion affect both types of basins. Ancient back-arc basins should be identifiable on the basis of their temporal relations to magmatic arcs and the volcanic influence in their sedimentary sequence, but distinguishing between small and major ocean basins is often difficult. Narrow marginal basins may collapse following accumulation of a thick sediment pile, but most basins close by subduction. Similarities are recognized between the present-day SW Pacific and the formative stage of the North American Cordillera. The Late Mesozoic palaeogeography of the Western Alps resembles the complex of small ocean basins and continental fragments west of the Norfolk Ridge, and the Ordovician palaeogeography of central Newfoundland bears close resemblance to the assemblage of back-arc basins, remnant arcs and active arc east from the Norfolk Basin.