New Zealand Journal of Geology and Geophysics abstracts

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Provenance of Permian–Triassic volcaniclastic sedimentary terranes inNew Zealand: evidence from their radiogenic isotope characteristics and detrital mineral age patterns

C. J. Adams

Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand

M. E. Barley

Department of Geology & Geophysics
University of Western Australia
Nedlands, WA 3907, Australia

R. Maas

Department of Earth Sciences
La Trobe University
Bundoora, VIC 3063, Australia

M. G. Doyle

Department of Geology & Geophysics
University of Western Australia
Nedlands, WA 3907, Australia

Abstract  Detrital mineral age patterns, Rb-Sr age, and initial strontium isotope ratio variations are reported for metasediments of the Brook Street, Dun Mountain-Maitai, and Murihiku Terranes (informally grouped as “central arc terranes”) of New Zealand. U-Pb SHRIMP detrital zircon age populations in Late Permian Tramway Formation, sandstones of the Dun Mountain-Maitai Terrane in Nelson and Southland, New Zealand, show restricted Late Permian (253–268 Ma) and broader Devonian–Carboniferous (330–373 Ma) age components in about equal proportions, with a minor (<20%) proportion of early Paleozoic and Mesoproterozoic ages. The Permian component is related to contemporaneous volcanic inputs, whereas the older Devonian–Carboniferous component is derived from a mixture of exhumed continental crust of Lachlan Fold Belt, and possibly New England Fold Belt age characteristics. A detrital zircon age population of Jurassic Barretts Formation sandstone of the Brook Street Terrane in Wairaki valley, Southland, carries a major (75%), dominantly Middle Jurassic to Late Triassic (170–230 Ma) component derived from contemporary volcanic inputs of uncertain origin, and a minor (<25%) Middle Triassic to Late Permian (229–254 Ma) component. Rb-Sr isochron ages (t) of Brook Street, Dun Mountain-Maitai, and Murihiku Terrane metasediments (and their initial ⁸⁷Sr/⁸⁶Sr ratios (i) at the time of metamorphism), reveal cooling age patterns consequent upon low-grade metamorphism in latest Triassic and earliest Jurassic times. The (t)-(i) data define a central arc terranes group consistently less radiogenic than Permian and Triassic time correlatives in the Torlesse Supergroup of the Rakaia Terrane. This feature suggests a provenance that includes sediment detritus dominantly from less radiogenic I-type igneous sources in both Lachlan and New England Fold Belts in similar proportions, and with little contribution from their Precambrian and early Paleozoic hinterlands.

Keywords  Permian; Triassic; volcaniclastic sediments; U-Pb geochronology; Rb-Sr; strontium isotopes; terranes; provenance

G01009 Received 24 April 2001; accepted 3 April 2002
New Zealand Journal of Geology & Geophysics, 2002, Vol 45: 221–242
0028–8306/02/4502–0221 $7.00/0 © The Royal Society of New Zealand 2002

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