Provenance of Permian‐Triassic volcaniclastic sedimentary terranes in New Zealand: Evidence from their radiogenic isotope characteristics and detrital mineral age patterns

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, DunMountain-Maitai, and Murihiku Terrane metasediments (and their initial 87 Sr/ 86 Sr 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.

Episodicity of Mesozoic terrane accretion along the Pacific margin of Gondwana: implications for superplume-plate interactions

“…This deformation is interpreted to have resulted from collision between the Torlesse Terrane and Caples Terrane (Mortimer 1993), and corresponds in time to the Rangitata I orogeny (Bradshaw et al 1981). Rb-Sr method isochron ages of Brook Street, Dun MountainMaitai, and Murihiku Terrane metasediments of South Island show cooling age patterns that indicate low-grade metamorphism in latest Triassic and earliest Jurassic times (Adams et al 2002). This is possibly coincident with conglomerate deposition from 200-180 Ma that recorded docking between the Median Tectonic Zone and Brook Street terranes .…”

Tracing the Caples Terrane through New Zealand using detrital zircon age patterns and radiogenic isotope signatures

“…Analogous data from Permian, Triassic, and Jurassic fossiliferous localities in the adjacent Torlesse, Waipapa, and dun mountain-maitai Terranes have been attributed to widespread regional metamorphism associated with the Rangitata Orogeny, Phases i and ii, during the latest Triassic to early Jurassic and early Cretaceous, respectively (Adams & Graham 1996, and a more local event in the early Triassic (Adams et al 2002;Adams & maas 2004a). The Caples/Pelorus Rb-Sr ages thus well reflect the latter two metamorphic events.…”

“…The early Jurassic metamorphism is widespread, northeast of the Caples Terrane, throughout the Torlesse Terrane of South Canterbury (Adams & maas 2004a), and to the east it is similarly well recorded within the anomalous Caples block (Tuapeka Group) of eastern Otago (Adams & Robinson 1993;Adams & Graham 1997) and the Chrystalls Beach Complex . The Triassic metamorphism is well dated in the Permian sector of the Torlesse Terrane in South Canterbury at c. 235 ma (Adams & maas 2004a) and in maitai Group metasediments immediately to the west of the Caples Terrane in northern Southland and Nelson at c. 210-235 ma (Adams et al 2002). At the Caples/ dun mountain-maitai Terrane boundary on the west side of the mavora lakes ( fig.…”

Jurassic silicic volcanism in the Transantarctic Mountains: Was it related to plate margin processes or to Ferrar magmatism?

“…5). In the New Zealand region, parts of the Brook Street and Murihiku terranes indicate an Early Jurassic magmatic arc (Adams et al, 2002), and the Bounty Islands granite has an age of 183±9 Ma (Adams and Campbell, 2005). The Jones Mountains granite has an age of 198±2 Ma (Pankhurst et al, 1993), and a pluton in central Antarctic Peninsula an age of 181 Ma (Leat et al, 1995).…”