Basement geology of Taranaki and Wanganui Basins, New Zealand

Detailed mapping and sampling on Turoa skifield and surrounding areas on Mt Ruapehu has enabled identification of individual flow packets that represent small scale eruptive events during the major cone-building episodes previously identified on Ruapehu by Graham & Hackett. The area is dominated by plagioclase-pyroxenephyric andesitic lavas of Mangawhero Formation, which are petrographically and geochemically typical of post-120 ka Ruapehu lavas. Although the lavas are from a relatively small area of the volcano, geochemical and isotopic compositions show a range in variation similar to that observed for the entire volcano. Examination of geochemical variations between individual flow packets and also between sequential C98039Received 15 October 1998; accepted 15 June 1999 lava flows indicates complex processes of assimilation and influx of "new", variably evolved and fractionated magmas into high level magma chambers. These chambers are most likely heterogeneous, and individual eruptions may also sample compositionally distinct regions of the same chamber. It is probable that a complex plumbing system exists beneath Ruapehu with at least two levels of magma storage, evolution, and crustal interaction. Consequently, attempts to numerically quantify such a complex system using models such as assimilation-fractional crystallisation processes are inherently oversimplifications.

Section: Discussionmentioning

confidence: 96%

Stratigraphy and geochemistry of the Turoa area, with implications for andesite petrogenesis at Mt Ruapehu, Taupo Volcanic Zone, New Zealand

Waight

Price

Stewart

et al. 1999

“…later discussion of the northern extent of the Torlesse terranes). Long-distance transport does not appear to be an obstacle to this interpretation, since clasts under consideration are of granule size, and sediment gravity flows are capable of transporting material for hundreds of kilometres (e.g., Simm & Kidd 1984 Mortimer et al (1997Mortimer et al ( , 1999. E, area removed by later uplift and erosion (Walcott 1998).…”

Section: Modelmentioning

confidence: 99%

“…The boundary between the Waipapa composite and Torlesse accretionary terranes in the North Island is nowhere exposed, though approximate positions have been determined in the central and southern parts of the North Island (Beetham & Watters 1985;Mortimer et al 1997). The matter of a possible northern Torlesse/Waipapa Terrane boundary in the Bay of Plenty area will also be discussed in this paper (cf.…”

Section: Introductionmentioning

confidence: 99%

“…Fig. 1 Basement terranes of the North Island, New Zealand, excluding younger covering strata, modified after Aita & Sporli (1992), Black (1994), Mortimer (1995a), and Mortimer et al (1997). Rocks of the Median Tectonic Zone are outlined in their assumed offshore distribution, all other terranes are presented in their interpreted onshore extent.…”

Section: Introductionmentioning

confidence: 99%

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Terrane affiliation and terrane boundaries of Mesozoic accretionary complexes, northeastern North Island, New Zealand: Some implications from recycled elastics

Leverenz

Ballance

2001

In the late Mesozoic Waioeka petrofacies in northeastern North Island, New Zealand, sandstone pebbles differ significantly in petrography from their enclosing sandy conglomerate matrix, and yield contrasting provenance signatures. The compositional contrast demonstrates the extrabasinal origin of most of the analysed clasts. Differences in clast provenance have been used to review boundaries and the terrane affiliation to the neighbouring Torlesse and Waipapa composite terranes.A previously postulated Cretaceous large-scale dextral strike-slip displacement of eastern North Island along the Wellington-Mohaka-Whakatane Fault is supported by these data. The timing for this movement can be further bracketed between c. 98 and 85 Ma. The Waioeka and Omaio petrofacies, formerly attributed to the Torlesse terranes as the Waioeka Subterrane, are reinterpreted to constitute a separate terrane (Waioeka-Mata River Terrane). However, the westernmost portion of the former Waioeka Subterrane, west of the Wellington-Mohaka-Whakatane Fault, is considered to be part of the Waipapa composite terrane.

“…1 Location of study area on Coromandel Peninsula, North Island, shown relative to distribution of Mesozoic basement terranes, general areas of suprabasement (Neogene, Late Cretaceous) strata, outline of the Wanganui Basin, and main area of Kawhia Syncline. Based on Kamp & Liddell (2000) and Mortimer et al (1997). Dix & Nelson-Torehina Fmn, provenance and geochemistry Torlesse Terranes west and south, respectively, of the study area (Ballance 1988;Baker & Staveley Parker 1989).…”

Section: Geological Settingmentioning

confidence: 99%

Provenance and geochemistry of exotic clasts in conglomerates of the Oligocene Torehina Formation, Coromandel Peninsula, New Zealand

Dix¹,

Nelson

2003

Non-marine pebble to cobble conglomerates of the lower Torehina Formation (Oligocene) crop out along western Coromandel Peninsula and overlie, with strong angular discordance, continental-margin metasedimentary rocks (Manaia Hill Group) of Mesozoic (Late Jurassic to ?Early Cretaceous) age. The conglomerates contain provenance information that identifies a pre-Oligocene depositional history obscured by the unconformable juxtaposition of these Tertiary and Mesozoic strata.Most clasts in the lower Torehina Formation are visually similar to local bedrock lithologies, including metamorphosed sandstones and argillites, but are kaolinitic and contain more detrital and authigenic chert, quartz, and potash feldspar. Local derivation of these clasts seems unlikely. By comparing geochemical ratios with those defined for continental margin sandstones, and well characterised New Zealand tectonic terranes, we interpret the majority of clasts in the lower Torehina Formation to have been derived from a dissected orogen, with mixtures of felsic and volcanogenic-derived sediment. The most likely sources are the Waipapa and Torlesse Terranes.The remaining 20-30% of the clasts in the lower Torehina Formation were originally friable, are coarse grained, and appear to be lithologically exotic relative to known metamorphosed sandstones in basement terrane sources on North Island. Some clasts contain coal laminae and particles, and all contain detrital kaolinite as lithic fragments and matrix. Such characteristics imply a non-marine to marginalmarine source containing sediment derived from strongly weathered granite or granodiorite. Mechanical fragility implies a likely proximal, easily erodible source. We propose that this group of clasts was derived from an Upper Cretaceous sedimentary cover, either part of a locally developed basin fill or part of a once regionally extensive cover on North Island. Either case defines a more widely distributed Cretaceous source than found today.