New Zealand Journal of Geology and Geophysics abstracts
Emplacement depths of Paleozoic-Mesozoic plutons from western New Zealand
estimated by hornblende-Al geobarometry
A. J. TULLOCH
Institute of Geological & Nuclear Sciences
Dunedin Research Centre
Private Bag 1930
Dunedin, New Zealand
G. A. CHALLIS*
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
*Present address: 16 Grey Street, Motueka, New Zealand.
Abstract Emplacement depths of 33 rocks from 27 Paleozoic and
Mesozoic plutons from western New Zealand have been estimated utilising the
hornblende-Al barometer of Anderson and Smith. Emplacement depths for plutons
from the Median Batholith/Median Tectonic Zone (Median and Separation Point
Suites) plutons range from 8 to 27 km. The greatest emplacement depths are
found along the western edge of the batholith, in areas dominated by plutons of
the Separation Point Suite; together with geochronological data they suggest
significant uplift in the interval 118 to c. 110 Ma. Emplacement depths of
c. 8-10 km are typical along the eastern side of the batholith in mainly
Triassic plutons. No trend along the length of the batholith is apparent.
Plutons associated within the lower plates of metamorphic core complexes were
emplaced in the range 19-23 km, and were uplifted over a similar, but possibly
slightly later, time interval. No significant consistent difference in
amphibole type or chemistry was observed between the suites. Epidote believed
to be of magmatic origin occurs in 11 plutons which record emplacement
pressures of 3.1 kbar or greater, in conflict with the notion that such epidote
indicates pluton emplacement pressures >=6-8 kbar.
Keywords hornblende; amphibole; granite; plutons; epidote;
tectonics; Mesozoic; geobarometry; Westland; Nelson; Fiordland; Stewart
Island
New Zealand Journal of Geology & Geophysics, 2000, Vol. 43:
555-567
0028-8306/00/4304-0555 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (1517K); (scanned from paper original: notes about this process)
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