New Zealand Journal of Geology & Geophysics abstracts
Alteration, age, and emplacement of the Tangihua Complex Ophiolite,
New Zealand
K. N. Nicholson1*
P. M. Black2
C. Picard3
P. Cooper1
C. M. Hall4
T. Itaya5
1Department of Geology
Ball State University
Muncie, IN 47306, USA
2Department of Geology
University of Auckland
Private Bag 92019
Auckland 1142, New Zealand
3University of New Caledonia
Laboratoire de Géologie
BP 4477 Nouméa, New Caledonia
4Department of Geological Sciences
University of Michigan
2534 C.C. Little Building
425 E University Ave
Ann Arbor, MI 48109-1063, USA
5Research School of Natural Sciences
Okayama University of Science
Ridai-cho, Okayama 700-0005, Japan
*Corresponding author: knichols@bsu.edu
Abstract The Tangihua Complex, New Zealand,
represents an upper sequence of Late Cretaceous oceanic crustal
material: massive basalt flows, pillow lavas, and dolerites. Three
phases of alteration are preserved within the complex, each
characterised by zeolite precipitation, which correlate to
stratigraphic position. The mylonitised sole contains greenschist
assemblages (c. 325°C) grading upwards into the
initial phase of alteration (250—300°C), and
is
characterised by actinolite, epidote, albite, and Na-rich zeolites.
This phase is cut by lower temperature veins of chlorite-smectite and
Ca-rich zeolites. The final alteration phase (<50°C)
precipitated K+ and Ca2+-rich minerals, including
apophyllite and calcite.
Disruption of Ar/Ar spectra around 50 Ma
correlate with rifting in the Loyalty Basin and initiation of obduction
along the Loyalty—Three Kings Ridge system. We suggest
that these
events resulted in initial dismemberment, alteration, and movement of
the ophiolite, whereas Ar/Ar plateaux at 25—35 Ma
correspond to
ophiolite emplacement and the last phases of alteration.
Keywords alteration; ocean floor metamorphism;
Ar/Ar dating; tectonics; Southwest Pacific
G06029; Online publication date 18 May 2007; Received 22 September
2006; accepted 16 April 2007
New Zealand Journal of Geology & Geophysics, 2007, Vol. 50:
151—164
0028-8306/07/5002-0151 © The Royal Society of New Zealand 2007
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