Petrology and petrogenesis of volcanic rocks from the Taupo Volcanic Zone: a review

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: Geological Settingmentioning

confidence: 99%

“…1) (Graham et al 1995). North of New Zealand, volcanic activity along the Kermadec Ridge is dominantly basaltic (Ewart et al 1977), whereas volcanism in the North Island of New Zealand is dominantly (>90%) rhyolitic, with considerably lesser andesitic activity and sparse (>1%) basaltic volcanism (Cole 1986;Gamble et al 1990).…”

Section: Geological Settingmentioning

confidence: 99%

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

“…In the late Miocene-Pliocene, voluminous and dominantly rhyolitk volcanism characterised the central and southern parts at the Coromandel Peninsula and Tauranga area. By 1.5 Ma BP, all arc volcanism was concentrated along the Taupo White Island -Kermadec arc (Graham et al 1995;Wilson et al 1995), but the volcanic products of this youngest arc are also found on the southern part of Coromandel Peninsula.…”

mentioning

confidence: 99%

Geophysical characterisation of large silicic volcanic structures in the Coromandel Peninsula, New Zealand

Malengreau

Skinner

Bromley

et al. 2000

Previous stratigraphic and tectonic studies of Coromandel Peninsula, New Zealand, have defined regionally significant structures, including calderas, of Miocene age. A new gravity map of the area reveals significant details not seen in the earlier geophysical surveys. Results from a new low-level aeromagnetic survey and from two new magnetotelluric resistivity soundings help interpret the volcanic structures. 2-D/2.5-D models are used to visualise the internal structure.

“…2 and 3, along with a field for the present-day whole rock Pb isotopic compositions of Jurassic greywackes from the Pahau ('Younger Torlesse') Terrane in North Island, New Zealand (data from Graham et al 1992, andMcCulloch et al 1994).…”

Section: Resultsmentioning

confidence: 99%

“…3 (A, B) Lead isotopic compositions of sulphides from goldbearing veins and vein breccias in the northwestern Otago and Southern Alps, together with fields for sulphide Pb compositions from gold-bearing veins and shear zones in the main part of the Otago Schist belt (from Mortensen et al 2010). The present-day fields for Pb isotopic compositions of Pahau Terrane greywackes on North Island, New Zealand, are shown for reference (data from Graham et al 1992;McCulloch et al 1994). Age-corrected fields for Pb isotopic compositions of Pahau Terrane greywackes at 25 Ma are also shown; these were calculated using Pb evolution parameters as discussed in the text.…”

Section: Discussionmentioning

confidence: 99%

Lead isotope constraints on the origin of Cenozoic orogenic gold systems in the Southern Alps and northwestern Otago, South Island, New Zealand

Mortensen

Craw

MacKenzie

et al. 2010

Lead isotopic compositions were determined for sulphides from Pliocene-Pleistocene gold-bearing veins in the Alpine Schist and from Miocene gold-bearing veins and vein breccias from the Shotover-Macetown area in the northwest Otago Schist belt. The lead isotopic signatures are consistent with derivation of Pb in the vein minerals predominantly from metasedimentary rocks that underlie the region. Differences in Pb isotopic signatures between deposits are interpreted to result from lateral and vertical lithological variability within the source rock mass. The host rocks also contain metabasic rocks with N-MORB, E-MORB or within-plate basalt chemistry. However, the observed Pb isotopic signatures in the gold-bearing veins preclude incorporation of significant amounts of Pb from the metabasites. The Pb isotopic signatures of lamprophyre dikes that were intruded into the Otago Schist coeval with Miocene gold mineralisation are distinctly more radiogenic than those of the hydrothermal veins. Thus, although the lamprophyre dikes were emplaced into similar extensional structural sites to the gold-bearing veins, there was no genetic relationship between lamprophyre dikes and gold mineralisation.