Lower to Middle Miocene Sediments on Maewo, New Hebrides, and their Relevance to the Development of the Outer Melanesian Arc System

Abstract

Lower to Middle Miocene sediments on Maewo contain clasts derived from the 'Vitiaz arc', a former tholeiitic volcanic belt similar in age, lithology and geochemistry to Upper Eocene?Middle Miocene rocks on Viti-Levu, Fiji. The configuration of Outer Melanesia from the New Hebrides through Fiji to Tonga-Lau in the Early to Middle Miocene was a double arc compising a frontal arc (Vitiaz arc ? Viti Levu ? Tonga Ridge) and a rear arc (Western Belt?Lau Ridge) couple. Tectonism in the Middle Miocene brought about inter-arc rifting between the Vitiaz arc?Western Belt couple and the anti-clockwise rotation of Viti Levu into a rear arc position; further fragmentation and the development of marginal basins had also affected the Tonga-Lau couple by the Early Pliocene. Mio-Pliocene lavas of the New Hebrides Eastern Belt were erupted in the Vitiaz arc?Western Belt inter-arc basin in response to further rifting and crustal thinning associated with the developing proto-North Fiji Basin. Expansion of this basin was accompanied by subduction reversal from the eastern to western margins of the New Hebrides Ridge which then migrated south-westwards to its present position. The present configuration of the New Hebrides Ridge is a typical of that usually attributed to SW Pacific arc systems.