New Zealand Journal of Geology and Geophysics abstracts
The Paleozoic–Mesozoic recycling of the Rakaia Terrane, South
Island, New Zealand: sandstone clast and sandstone petrology,
geochemistry, and geochronology
Anekant M. Wandres
John D. Bradshaw
Department of Geological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand
anekant.wandres@canterbury.ac.nz
Trevor Ireland
Geochronology and Isotope Geochemistry
Research School of Earth Sciences
The Australian National University
Canberra ACT 0200, Australia
Abstract The Torlesse terranes—part of the New
Zealand Eastern Province—are accretionary complexes that comprise an
enormous volume of quartzofeldspathic sandstones and mudstones with
subsidiary conglomerates plus minor oceanic assemblages. Two terranes
are recognised in the South Island—the Permian to Late Triassic Rakaia
Terrane and the Late Jurassic to Early Cretaceous Pahau Terrane.
Sandstone clasts from two Rakaia Terrane and two Pahau Terrane
conglomerates were collected. We present the first combined detailed
information on petrography and geochemistry of Torlesse conglomerate
sandstone clasts and use our own and published U-Pb SHRIMP detrital
zircon age data to demonstrate the recycling of the Rakaia Terrane into
Rakaia strata itself and into Pahau Terrane strata. Sandstone clast
major and trace element chemical data largely support petrographic
observations derived from thin-section analysis. The similarities of
petrographic and geochemical data between sandstone clasts from the
Rakaia Terrane and Rakaia sandstones suggest that clasts in the Permian
Te Moana and Late Triassic Lake Hill Conglomerates were derived by
autocannibalistic reworking of older, consolidated, Rakaia sediments.
Data from sandstone clasts from the Pahau Terrane suggest that uplift
of the Rakaia Terrane continued into the Cretaceous. These Pahau
Terrane clasts indicate that at the time of the Pahau sedimentation
Permian to early Late Triassic Rakaia rocks were exposed and recycled
into the Pahau Basin.
Keywords sandstone; provenance; Terrane recycling;
petrography; geochemistry; zircon; geochronology; Pahau Terrane; Rakaia
Terrane; Gondwana margin
G03067; Received 3 November 2003; accepted 13 July 2004; Online
publication date 25 May 2005
New Zealand Journal of Geology & Geophysics, 2005, Vol. 48:
229–245
0028–8306/05/4802–0229© The Royal Society of New Zealand 2005
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