Significance of palaeomagnetic data from the oceanic Poya Terrane, New Caledonia, for SW Pacific tectonic models

Results from a palaeomagnetic study of pillow basalts and associated pelagic sediments of the Late Cretaceous–Palaeocene Poya Terrane of New Caledonia are presented. The Poya Terrane forms a nappe that was thrust SW over the island, i.e. the Pacific side, in the middle Eocene. Data from four outcrops (nine sites), spread over 250 km, yield a normal polarity tilt-corrected mean inclination of −57.2°, where α95=11.2° and k=67.4, which suggests formation at 37.8° (±12.1°) S. The between-outcrop declinations are, unfortunately, too scattered to be used in regional tectonic discussions; they indicate rotations that are localised and sometimes very large. Following reference to SW Pacific Late Cretaceous–Palaeogene plate tectonic reconstructions, the inclination data suggest that the Poya Terrane formed close to the New Caledonian portion of the Indo–Australia plate. This interpretation is consistent with tectonic models where the Poya Terrane is generated in a marginal basin immediately to the northeast of New Caledonia during the break-up of east Gondwana. The terrane was thrust over New Caledonia in the middle Eocene, possibly in response to a change in relative motion of the Australian and Pacific plates at about this time. A short time later it was overthrust by a supra-subduction zone ultramafic nappe and together they have since drifted northwards as passengers on the Australia Plate.