New Zealand Journal of Geology and Geophysics abstracts
Heavy minerals in the Torlesse Terrane of the Wellington area, New Zealand
DAVID SMALE
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
Abstract Heavy minerals from dated sandstones of the Torlesse
Terrane in the Wellington area show several distinct assemblages. Samples from
the Rakaia Subterrane (n = 19) have assemblages of two types:
one dominated by secondary minerals (mainly in the Terawhiti area), and one by
detrital biotite (mainly in the eastern part of the subterrane). Both types
were present in the Kapiti Island area. Pahau (n = 3) and Esk
Head samples of Pahau affinity (n = 3) are distinct from
Rakaia samples in containing more than trace amounts of garnet, and suggest a
different provenance (i.e. little reworking). The remaining two Esk Head
samples resemble the biotite-rich assemblage of the Rakaia but contain minor
pyroxene and no epidote minerals. The distinction between epidote-rich Pahau
and biotite-rich Rakaia assemblages has a parallel in North Canterbury.
Semi-opaque debris and pumpellyite indicate low-grade metamorphism of Pahau
rocks and of some Rakaia rocks from near Cape Terawhiti. However, the
difference between the two Rakaia assemblages is unlikely to be due solely to
this metamorphism, as zircon morphology and garnet compositions suggest
different provenances. Many of the garnet compositions in Pahau and Esk Head
samples are distinct from those in Rakaia samples, suggesting that the Rakaia
Subterrane was not the provenance.
Systematic distinctions such as these in Torlesse rocks offer potential for
refining provenances of overlying Cretaceous-Cenozoic sandstones.
Keywords Torlesse; Wellington; heavy minerals; provenance;
metamorphism
New Zealand Journal of Geology and Geophysics, 1997, Vol. 40: 499-506
0028-8306/97/4004-0499 $7.00/0 (c) The Royal Society of New Zealand
1997
PDF file of entire paper: medium quality (791K); (scanned from paper original: notes about this process)
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