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 tiltcorrected mean inclination of -57.2°, where alpha 95=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.