New Zealand Journal of Geology and Geophysics abstracts
The Awhitu volcanic complex, an offshore Pliocene volcano in the northern
Taranaki Basin, New Zealand
VAUGHAN STAGPOOLE
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
Abstract Interpretation of seismic reflection data indicates
that a volcanic complex of Pliocene age (between 5 and 2.2 Ma) lies
offshore in the northernmost Taranaki Basin at 173.8deg.E, 37.4deg.S. The
volcanic complex, here named the Awhitu volcanic complex, appears to be
completely buried beneath late Pliocene and younger sediments. It has an
irregular, unsymmetrical shape with at least three distinct peaks, and
interpretation of all available seismic reflection data indicate it to be
<700 m thick. Simple gravity and magnetic models, constrained by the
seismic reflection data, predict that the Awhitu volcanic complex is comprised
of rocks with a bulk density of 2350-2600 kg/m3 and a bulk
magnetisation of 3.5-12 A/m. A review of the density and magnetisation of
rocks from the region indicates that Miocene and Pliocene andesitic volcanoes
in the Taranaki Basin have a similar bulk density, but a lower bulk
magnetisation than the Awhitu volcanic complex. The magnetisation is, however,
within the observed range of basaltic rocks from volcanoes on the west coast of
the North Island, and although it is possible for the Awhitu volcanic complex
to be of andesitic composition, results from magnetic modelling suggest that it
is composed of basaltic rocks. The morphology of the volcanic complex is also
more characteristic of basaltic volcanic centres. The Awhitu volcanic complex
is likely to have a similar origin to the onshore Pliocene-Pleistocene
volcanoes of the South Auckland and Waikato districts, and if it is
subduction-related, its location relative to onshore volcanoes may reflect the
eastward migration of the subduction zone in the Pliocene-Pleistocene.
Keywords Awhitu volcanic complex; western North Island;
Taranaki Basin; Pliocene; volcanism; density; magnetisation; gravity modelling;
magnetic modelling
New Zealand Journal of Geology & Geophysics, 1999, Vol. 42:
327-334
0028-8306/99/4203-0327 $7.00/0 (c) The Royal Society of New Zealand
1999
PDF file of entire paper: medium quality (850K); (scanned from paper original: notes about this process)
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