New Zealand Journal of Geology and Geophysics abstracts
Geological interpretation of a deep seismic reflection profile across
the Eastern Province and Median Batholith, New Zealand: crustal architecture
of an extended Phanerozoic convergent orogen
N. Mortimer
Institute of Geological & Nuclear Sciences
Private Bag 1930
Dunedin, New Zealand
F. J. Davey
A. Melhuish1
J. Yu
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
N. J. Godfrey2
Department of Earth Sciences
University of Southern California
Los Angeles, California, USA
1Present address: Veritas DGC Ltd, P.O. Box 100, Mina Al Fahal,
PC 116 Sultanate of Oman.
2Present address: Landmark EAME, Hill Park South, Springfield
Drive, Leatherhead KT22 7NL, United Kingdom
Abstract An offshore seismic reflection profile provides
new information on the tectonic evolution of the Paleozoic-Mesozoic margin
of southern Gondwanaland. The 550 km long composite South East South Island
(SESI) profile extends from near Christchurch to near Stewart Island, New
Zealand. It crosses the Eastern Province geological basement terranes and
ends in the Median Batholith. The Median Batholith and all the basement
terranes appear to extend down to middle or lower crustal levels and are
not minor thin-skinned fault slices. A discontinuous, but generally strong
Moho reflector is observed along the profile varying from c. 22 to 32 km
depth. Upper to mid-crustal reflections can be related to Murihiku Terrane
bedding and Otago Schist foliation. Gravity and magnetic measurements indicate
that the Maitai Terrane dips northeast beneath the Otago Schist. The SESI
profile contains no evidence for stranded slabs of Mesozoic oceanic crust
beneath the Eastern Province. The Moho depth along the SESI profile, particularly
under the Median Batholith and Otago Schist accretionary prism, is markedly
shallower than in other circum-Pacific Mesozoic orogens. This, and and the
geometry of several fault-related reflectors in the SESI profile, can be
attributed to significant out-of-profile Late Cretaceous extension related
to Gondwanaland breakup. Three regions of strong, deep crustal reflectivity
are present, and their association with thinner crust suggests they may also
be extension-related features.
Keywords reflection seismology; SESI profile; crustal
structure; tectonics; South Island; New Zealand; Moho; Eastern Province terranes;
Median Batholith; Paleozoic; Mesozoic
G01021 Received 26 June 2001; accepted 25 June 2002 ; published 27 September
2002
New Zealand Journal of Geology & Geophysics, 2002, Vol. 45: 349-363
0028-8306/02/4503-0349 $7.00/0 © The Royal Society of New Zealand
2002
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