New Zealand Journal of Geology and Geophysics abstracts
Deep-ocean record of major late Cenozoic rhyolitic eruptions from New Zealand
Lionel Carter
National Institute of Water & Atmospheric Research Ltd
P.O. Box 14 901
Wellington, New Zealand
Brent Alloway
Institute of Geological & Nuclear Sciences
Private Bag 2000
Taupo, New Zealand
Philip Shane
Department of Geology
University of Auckland
Private Bag 92 019
Auckland, New Zealand
John Westgate
Geology Department
University of Toronto
Ontario M5S 1A1, Canada
Abstract A 12 m.y. record of large rhyolitic eruptions from the Coromandel (CVZ) and Taupo (TVZ) Volcanic Zones of New Zealand is contained in cores retrieved by Leg 181 of the Ocean Drilling Program. Site 1124, located 670 km from the TVZ, has a maximum of 134 macroscopic tephra layers with a total thickness of 13.18 m. These units, along with between 7 and 63 tephras from 3 other sites, were dated by a combination of magnetostratigraphy, biostratigraphy, isothermal plateau fission track determinations, and geochemical correlation with onshore tephra deposits. Additional time control for the last 3 m.y. came from an orbitally tuned, benthic, oxygen isotope profile for Site 1123.
Results extend the incomplete terrestrial record of volcanism by placing the
first major rhyolitic eruption in the CVZ at c. 12 Ma, c. 1.6-1 m.y. earlier
than previously known. Tephras became thicker and more frequent from the late
Miocene into the Quaternary-a trend that probably reflected (1) more frequent
and intense volcanism and (2) reduced distances between sources and depositional
sites on the evolving Australian/Pacific plate system. The passage from CVZ
to Quaternary TVZ occurred without a major hiatus in activity, suggesting the
transition was gradational. The ensuing TVZ volcanism was more continuous than
known previously from the onshore geology.
Ash dispersal was primarily eastward,
highlighting the dominance of westerly winds since the middle Miocene. Nevertheless,
variations in dispersal patterns suggest periodic changes in wind direction/speed
and/or ejection of ash beyond the Roaring Forties.
Keywords volcanism; Taupo Volcanic Zone; Coromandel Volcanic Zone; history; Ocean Drilling Program
G03061; Received 25 June 2003; accepted 10 December 2003; Online publication
date 7 September 2004R
New Zealand Journal of Geology & Geophysics, 2004, Vol. 47: 481-500
0028-8306/04/4703-0481 © The Royal Society of New Zealand 2004
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