New Zealand Journal of Geology and Geophysics abstracts
Geophysical characterisation of large silicic volcanic structures in the
Coromandel Peninsula, New Zealand
BARBARA MALENGREAU1,2
DAVID SKINNER3,4
CHRIS BROMLEY5
PHILIPPA BLACK1
1Geology Department
The University of Auckland
P.O. Box 92 019
Auckland, New Zealand
2Present address: PYROS SARL, 27 Route du Cendre, F-63800 Cournon
d'Auvergne, France.
3Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
4GeoGnostics Consultancy
New Zealand
5Wairakei Research Centre
Private Bag 2000
Taupo 2730, New Zealand
Abstract Previous stratigraphic and tectonic studies of
Coromandel Peninsula, New Zealand, have defined regionally significant
structures, including calderas, of Miocene age. A new gravity map of the area
reveals significant details not seen in the earlier geophysical surveys.
Results from a new low-level aeromagnetic survey and from two new
magnetotelluric resistivity soundings help interpret the volcanic structures.
2-D/2.5-D models are used to visualise the internal structure.
Basement greywacke and andesite signatures are observed in the northern and
western parts of Coromandel Peninsula, and in the areas of the Aldermen Islands
and Mercury Islands, offshore to the east. Rhyolite and ignimbrite signatures
define four main volcanic structures: (1) the Whitianga Caldera over the
Whitianga Volcanic Centre, with an estimated volume of low-density material of
179 km3, a diameter of 15 km, and a depth of
1-1.5 km; (2) the Kapowai Caldera, previously defined by geological
evidence, with a volume of remaining material of 256 km3 and a
depth of 1.1-1.4 km; (3) a north-south-trending area south of the Kapowai
Caldera which could be a trough filled with low-density silicic rocks and
includes the previously suggested but undocumented Wharekawa Caldera; and (4) a
trough filled with low-density silicic rocks offshore of the east coast of
Coromandel Peninsula.
Keywords Coromandel Peninsula; New Zealand; silicic volcanic
structures; calderas; gravity surveys; low-level aeromagnetic survey;
magnetotelluric resistivity soundings; hydrothermal alteration
New Zealand Journal of Geology & Geophysics, 2000, Vol. 43:
171-186
0028-8306/00/4302-0171 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (4599K); (scanned from paper original: notes about this process)
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