Paleomagnetic-tectonic study of the New Caledonia Koh Ophiolite and the mid-Eocene obduction of the Poya Terrane

Abstract

A paleomagnetic study was carried out on the allochthonous Late Paleozoic Koh Ophiolite of New Caledonia to determine its formation site. Four outcrops (20 sites) were sampled from weakly metamorphosed pillow lavas and dike rocks. Usable directional data were obtained from 18 sites, and 2 magnetization components were identified. A high-stability component thought to be of primary origin is recognised in 11 sites. It is westerly orientated, but the large spread of directions makes it impossible to deduce with any precision the latitude at which the Koh Ophiolite formed, a "subequatorial to mid-latitude Southern Hemisphere location" being the strongest justifiable statement. An overprint (partial/total) was identified in 9 sites/4 outcrops. It is northerly directed, upward dipping (c. -57.0 ± 5.8°; i.e., of normal polarity), and equates to a paleolatitude of 37.6 ± 6.2°S. The overprint may be tectonically significant; it corresponds to the position New Caledonia was at when it was overthust by the oceanic Poya Terrane in the middle Eocene.