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 pelagi c 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 outcrop s (nine sites), spread over 250 km, yield a normal polarity tilt-corrected mean inclination of -57.2 degrees, where alpha 95 = 11.2 degrees and k = 67 .4, which suggests formation at 37.8 degrees (+/-12.1 degrees) S. The betwe en-outcrop declinations are, unfortunately, too scattered to be used in reg ional tectonic discussions; they indicate rotations that are localised and sometimes very large. Following reference to SW Pacific Late Cretaceous-Pal aeogene plate tectonic reconstructions, the inclination data suggest that t he Poya Terrane formed close to the New Caledonian portion of the Indo-Aust ralia plate. This interpretation is consistent with tectonic models where t he Poya Terrane is generated in a marginal basin immediately to the northea st of New Caledonia during the break-up of east Gondwana. The terrane was t hrust over New Caledonia in the middle Eocene, possibly in response to a ch ange 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 ultra mafic nappe and together they have since drifted northwards as passengers o n the Australia Plate. (C) 2000 Elsevier Science B.V. All rights reserved.