期刊
NEW ZEALAND JOURNAL OF GEOLOGY AND GEOPHYSICS
卷 45, 期 2, 页码 -出版社
SIR PUBLISHING
DOI: 10.1080/00288306.2002.9514970
关键词
Permian; Triassic; volcaniclastic sediments; U-Pb geochronology; Rb-Sr; strontium isotopes; terranes; provenance
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 (330373 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 Sr-87/Sr-86 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.
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