New Zealand Journal of Geology and Geophysics abstracts
The Chrystalls Beach-Brighton block, southeast Otago, New Zealand:
petrography, geochemistry, and terrane correlation
D. S. COOMBS
C. A. LANDIS
Geology Department
University of Otago
P.O. Box 56
Dunedin, New Zealand
S. HADA
Research Institute for Higher Education
Kobe University
Kobe 657-8501, Japan
M. ITO
Graduate School of Science and Technology
Kobe University
Kobe 657-8501, Japan
B. P. ROSER
Department of Geoscience
Shimane University
1060 Nishikawatsu
Matsue 690-8504, Japan
T. SUZUKI
S. YOSHIKURA
Department of Geology
Faculty of Science
Kochi University
Kochi 780-8520, Japan
Abstract The Chrystalls Beach-Brighton coastal block in
southeast Otago has commonly has been placed in Caples Terrane, but has
recently been described as a geochemically anomalous area of uncertain terrane
affinity. Data points on discriminant diagrams occupy fields centred between
those for type Caples Group and Torlesse Terrane, overlapping both. The
psammites average 71.9% SiO2, closely comparable to Torlesse Terrane psammites,
in contrast to the majority of type Caples Group psammites (av. 64.3%) and
Waipapa Terrane psammites (64.4%). QFL plots show the Chrystalls Beach
psammites as a petrofacies distinct from those described hitherto for Torlesse
Terrane (lithic feldsarenites) and Caples Group and Murihiku Terrane
(volcarenites).
Phosphatic nodules in melange zones associated with metabasites and cherts in
the Chrystalls Beach Complex contain Middle Triassic radiolarians. Middle-Late
Triassic tube fossils Torlessia sp. and Titahia corrugata Webby
occur in the Chrystalls Beach Complex as in the Torlesse Terrane, but are
unknown in type Caples Group sediments in which the only dated fossils are
Permian.
Both the trench or trench-slope Chrystalls Beach-Brighton psammites and the
late Middle to early Late Triassic Kaihikuan sediments of the Murihiku Terrane
were derived from regions of largely felsic volcanism with underlying
granitoids. The geochemical match is imperfect and the sedimentary facies are
different. The Chrystalls Beach-Brighton block is unlikely to be a tectonically
introduced and atypical part of the Torlesse Terrane. It may be: (1) an
atypical and geochemically more evolved part of the Caples Terrane, younger
than dated rocks preserved in the type area, or (2) a separate terrane fragment
with a different history from its neighbours. A suggested correlation with the
North Island Waipapa Terrane invites questions as to the true terrane affinity
of the rocks concerned and of Caples-Waipapa relationships in general.
Keywords Caples Terrane; Torlesse Terrane; Chrystalls Beach
Complex; Murihiku Terrane; geochemistry; Otago Schist; Waipapa Terrane
New Zealand Journal of Geology & Geophysics, 2000, Vol. 43:
355-372
0028-8306/00/4303-0355 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (1940K); (scanned from paper original: notes about this process)
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