New Zealand Journal of Geology & Geophysics abstracts

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Ultra-fast early Miocene exhumation of Cavalli Seamount, Northland Plateau, Southwest Pacific Ocean

N. Mortimer

GNS Science
Private Bag 1930
Dunedin 9054, New Zealand
n.mortimer@gns.cri.nz

W. J. Dunlap

Research School of Earth Sciences
Australian National University
Canberra, ACT 0200, Australia

Present address Department of Geology & Geophysics, University of Minnesota, Minneapolis MN 55455, USA

J. M. Palin

Department of Geology
University of Otago
PO Box 56
Dunedin 9054, New Zealand

R. H. Herzer

GNS Science
PO Box 30368
Lower Hutt 5040, New Zealand

F. Hauff

IFM-GEOMAR Leibniz Institute for Marine Sciences
Wischhofstrasse 1-3
D-24148 Kiel, Germany

M. Clark

NIWA
Private Bag 14901
Kilbirnie, Wellington 6241, New Zealand

Abstract We present new photographic, petrological, geochronological, and isotopic data for gneissic and granitic rocks obtained from six sample stations on Cavalli Seamount during two cruises in 2002. These data lead to revision of earlier conclusions based on two dredges of schist in 1999. Based on c. 100 Ma ages of zircon cores, and whole rock petrochemistry and tracer isotopes, we interpret the protoliths of paragneisses and orthogneisses to probably have been sedimentary and plutonic correlatives of the Late Cretaceous Houhora Complex. U-Pb dating of low Th/U zircon rims confirms an earliest Miocene high-grade metamorphic episode. A cooling history based on Ar-Ar K-feldspar dating indicates ultra-rapid cooling (c. 2000°C/m.y.) and vertical exhumation (c. 100 mm/yr) of the rocks at 19.9 Ma. Our preferred tectonic model relates the amphibolite facies metamorphism to Northland Allochthon emplacement and the rapid exhumation to dextral transtension along the Vening Meinesz Fracture Zone system and/or a rapidly retreating Pacific trench.

Keywords    New Zealand; Southwest Pacific Ocean; Northland Plateau; Vening Meinesz Fracture Zone; Northland Allochthon; tectonics; exhumation; strike-slip faulting; geochronology; Miocene

G07013; Online publication date 28 February 2008; Received 28 June 2007; accepted 18 December 2007

New Zealand Journal of Geology & Geophysics, 2008, Vol. 51: 29–42
0028–8306/08/5101–0029  © The Royal Society of New Zealand 2008

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