Basement geology from Three Kings Ridge to West Norfolk Ridge, southwest Pacific Ocean: evidence from petrology, geochemistry and isotopic dating of dredge samples

We present new petrographic, X-ray fluorescence, electron microprobe, Ar-Ar radiometric, fission track, and Sr, Nd and Pb isotopic data for igneous and metamorphic rocks from 18 dredges from a number of basins and ridges in the southwest Pacific Ocean. The dredge samples can be divided into four groups: (1) Permian to Cretaceous gabbroids, granitoids and hornfelses from the West Norfolk and Wanganella Ridges; (2) mainly Cretaceous mafic igneous rocks from the Reinga Ridge and Vening Meinesz escarpment; (3) subduction-related Late Oligocene and Early Miocene basalts and shoshonites from the Three Kings and southern Norfolk Ridges; and (4) back-are basin and intraplate basalts of Early Miocene age in the South and North Norfolk Basins, respectively, and intraplate basalts of Pliocene age in the Reinga Basin. Our dredge data, combined with regional magnetic and gravity data, provide much-needed tests of earlier tectonic interpretations of the region. Correlatives of the Permian Brook Street Terrane and Mesozoic Median Tectonic Zone of onshore New Zealand clearly extend along the West Norfolk and Wanganella Ridges. The Three Kings Ridge was active at least in the 19- to 20-Ma period, and was probably generated above a west-dipping subduction zone. The Norfolk Basin was a back-are basin to this are, and had opened by 18-20 Ma. The oldest Cenozoic volcanic rocks in the region are 26-Ma subduction-related volcanic breccias on the southern Norfolk Ridge; they probably predate opening of the Norfolk Basin and associated eastward migration of the Three Kings Ridge. (C) 1998 Elsevier Science B.V. All rights reserved.