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

Abstract

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.

Andesites as Magmatic Liquids or Liquid-crystal Mixtures; Insights from Egmont and Ruapehu Volcanoes, New Zealand Research Article

“…Ruapehu first became active more than 230 000 years ago, periods of more intense activity occurring 200, 134, 45, 22 and <15 ka years ago [6]. The 1995-96 events were consistent with the eruptive style of the previous c. 2 ka [39]; prior to 2 ka eruptive activity was marked by more abundant lava effusion [40]. From 20 to 10 ka the eruption style from Ruapehu differed again, comprising frequent plinian pumice eruptions which culminated in the c. 10 ka pyroclastic flow events of the climactic Taurewa Eruptive Episode [41].…”

Using geochemistry as a tool for correlating proximal andesitic tephra: case studies from Mt Rainier (USA) and Mt Ruapehu (New Zealand)

“…Most published data pertains to the cone-building lava flow sequences Waight et al, 1999;Stockstill et al, 2003). In this study, our focus is on use of glass and whole-rock geochemistry to distinguish andesitic tephra.…”

“…Waight et al, 1999;Gamble Figure 7 Total alkali silica diagram (after Le Bas et al, 1986) comparing glass compositions in Ruapehu and Rainier tephra with those of tephra erupted from neighbouring volcanic centres (see Appendix 1 for representative data). All data normalised to a loss-free basis before plotting.…”

“…Mullineaux, 1974;Vallance and Donoghue, 1999;Waight et al, 1999;Donoghue and Neall, 2001). The proximal tephrostratigraphy at both volcanoes is, however, complex, and much of the detail of the recent volcanic record at these volcanoes is unresolved.…”

Reconstructing the largest explosive eruptions of Mt. Ruapehu, New Zealand: lithostratigraphic tools to understand subplinian–plinian eruptions at andesitic volcanoes

“…Research on the coeval andesitic volcanoes has principally concentrated on their effusive activity and petrology (e.g. Cole 1978;Hackett 1985;Cole et al 1986;Graham and Hackett 1987;Hackett and Houghton 1989;Graham et al 1990;Hobden et al 1996;Stewart et al 1996;Hobden 1997;Waight et al 1999;Gamble et al 2003;Price et al 2005), along with the tephras and lahars produced by their most frequent vulcanian-strombolian and phreatomagmatic historical eruptions (Houghton et al 1987;Cronin et al 1997aCronin et al , 1998Nakagawa et al 2002;Bonadonna and Houghton 2005). Donoghue (1991), Donoghue et al (1995a, b), Neall et al (1995), Wilson et al (1995), Cronin et al (1996a), Donoghue et al (1997), Cronin and Neall (1997), Nairn et al (1998), Nakagawa et al (1998), Donoghue et al (1999), and Hitchcock and Cole (2007) have also described some aspects of explosive eruptions that may be two to three orders of magnitude larger than recent examples.…”