Introduction to the special issue on Volcanism in Zealandia and the SW Pacific

ABSTRACT

The New Zealand Journal of Geology and Geophysics has prepared a two-part Special Issue on volcanism in Zealandia and the southwest Pacific. Part 1, published in 2020 as Issue 4 of Volume 63, summarises regional aspects of Zealandia volcanism as well as South Island and Antarctica volcanism. Part 2, published in 2021 as joint issue 2–3 of Volume 64, summarises North Island volcanism. In this preface, I summarise the content of these issues and point out some (but certainly not all) outstanding topics.

KEYWORDS:

• Volcanism
• Zealandia
• special issue
• Antarctica
• SW Pacific

Introduction

In 1986, the Royal Society of New Zealand published a 371-page special volume titled ‘Late Cenozoic Volcanism in New Zealand’ (Smith 1986) for the International Volcanological Congress held in Rotorua that same year. The articles in that book have been extensive references for New Zealand volcanic fields, but much has been discovered in the subsequent 35 years. With the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Scientific Assembly – an expanded successor of the International Volcanological Congress – planned to run in Rotorua in 2023, the New Zealand Journal of Geology and Geophysics has compiled a two-part Special Issue that offers a collection of updated articles addressing volcanoes and volcanism across Zealandia and surrounding areas, with topics spanning continental- to micro-scale. Part 1, published in 2020, provides regional summaries as well as South Island and Antarctic volcanism. Part 2, published in 2021, summarises North Island volcanism.

Developments since 1986 and papers in this volume

One of the most significant changes since the 1986 Late Cenozoic Volcanism in New Zealand has been the global recognition that the New Zealand islands form only the small emergent portion of a vast ∼5 M km² continent (Figure 1). This continent, Te Riu-a-Māui/Zealandia, is roughly half the size of Australia but 94% is beneath sea level (average elevation being about −1500 m). Therefore, while many of the Special Issue articles cover onshore volcanism, some offshore volcanic occurrences are described too; Mortimer and Scott (2020) briefly summarise the continental scale of Zealandia volcanism, and Bischoff et al. (2020) utilise seismic data to delineate the extent of buried offshore volcanic fields (Figure 1). Being largely underwater means that water-magma interaction has occurred throughout Te Riu-a-Māui/Zealandia’s volcanic history, and Németh and Kósik (2020) review this extensive record of hydro-volcanism. Volcanic eruptions often produced ash clouds, and the tephra record is summarised by Hopkins et al. (2021b) with Peti et al. (2021) providing a case study for the Auckland Volcanic Field (Figure 2(A)).

Figure 1. Locations shown in magenta correspond to topics covered in this Special Issue. The satellite gravity map is from LINZ.

The Special Issue features review papers on iconic stratovolcanoes such as Mount Taranaki (Figure 2(B)) (Cronin et al. 2021), Mount Ruapehu, Mount Tongariro and Mount Ngauruhoe (Figure 2(C)) (Leonard et al. 2021). Any summary of the Taupō Volcanic Zone (TVZ) must include Taupō, for which the Oruanui eruption is one of the largest known on Earth in recent times (Barker et al. 2021). In addition, there are reviews of Tarawera (Rowe et al. 2021), which was the former home of the world-renowned pink and white terraces, and Whakaari/White Island (Kilgour et al. 2021), New Zealand’s most active volcano. Case studies are presented on the crystal cargo occurring in TVZ andesitic lavas (Zellmer et al. 2021), spectral imaging of hydrothermal alteration of rocks at Mount Ruapehu (Kereszturi et al. 2021), hydrothermal sulphate associated with TVZ magmatic systems (Chambefort 2021), and gravity anomalies across the TVZ (Stagpoole et al. 2021). While the TVZ forms one of the most prominent manifestations of volcanism in New Zealand, Pittari et al. (2021) outline the history North Island volcanism immediately preceding the formation of the TVZ, with a particular focus on the Tauranga Volcanic Zone.

Figure 2. Some volcanic landscapes of New Zealand. A, Mount Eden in the Auckland Volcanic Field. B, Mount Taranaki. C, Arc volcanoes of the southern Taupō Volcanic Zone. D, Intraplate Dunedin Volcano of the Dunedin Volcanic Group. E, Intraplate Banks Peninsula volcano. Image credits Lloyd Homer, GNS Science.

Te Riu-a-Māui/Zealandia has a remarkable temporal and spatial record of intraplate volcanism. North Island contains intraplate volcanic provinces of Miocene to Holocene age, occurring from Northland to Waikato (Smith and Cronin 2020). The youngest intraplate eruption is the ∼500 year old Rangitoto eruption within the Auckland Volcanic Field (Hopkins et al. 2021a), which post-dates Polynesian arrival to New Zealand. South Island, too, has many intraplate volcanic provinces (Figure 2(D and E)), and this Special Issue features reviews of the Oligocene-Miocene Dunedin Volcanic Province, which at 7800 km² is the largest on-land intraplate volcanic province in the country (Scott et al. 2020a), the lamprophyric-carbonatitic Alpine Dyke Swarm in West Otago (Cooper 2020), and the Waiareka-Deborah Volcanic Field, which erupted continental shelf when almost all of Zealandia was submerged (Scott et al. 2020b). There remains debate on the origins of the Zealandia intraplate magmas, with asthenosphere, lithosphere and combinations of both having been suggested to be mantle reservoirs; this topic requires further work, but the mantle peridotite datasets summarised by Scott (2020) provide a foundation for examining the role of Zealandia’s mantle. Detailed micro-analytical studies of components within the intraplate magmas provide insight into how xenoliths of mantle (Auer et al. 2020) or crust (Scanlan et al. 2020) have reacted with host magma, as well as the formation of amphibole megacrysts in Westland and the Alpine Dyke Swarm (Serre et al. 2020).

Concepts about volcanism have also changed since 1986. Extensive research is now being undertaken on the hazards associated with volcanism. In this Special Issue, eruption scenarios are presented for the >1 M population of Auckland (Hopkins et al. 2021a), and Cronin et al. (2021) and Procter et al. (2021) cover the dangers of lahars on Mount Ruapehu and Mount Taranaki. Modern volcanological studies now commonly include remote sensing and geophysical techniques, and Hamling (2020) utilises satellite imagery to assess volcano deformation of Tongariro and White Island, whereas Kereszturi et al. (2021) combine petrological data with airborne hyperspectral imaging and aero-magnetic data to analyse flank instability on Mount Ruapehu.

It is important to acknowledge Zealandia’s volcanic connections to Gondwana. Prior to 84 Ma, Zealandia lay along the accretionary margin of Gondwana, and so there are opportunities to study volcanic record in some of the accreted terranes, such as the Permian Brook Street Terrane island arc assemblage, which is well exposed in southern South Island (Mawson et al. 2020). There are also similarities in the styles of volcanism between Zealandia and Antarctica (Smellie et al. 2020).

Where to from here?

Despite its wide content, this Special Issue is far from exhaustive in describing all Te Riu-a-Māui/Zealandia volcanic systems. This is in part because either some volcanoes already have up-to-date syntheses, or the fields have not had a comprehensive examination in recent times. The Tonga-Kermadec Arc, for example, was comprehensively reviewed in a collection of by papers in the Journal of Volcanology and Geothermal Research Special Issue ‘Making and breaking the arc: a volume in honour of Professor John Gamble’ (Wysoczanski et al. 2010). Regional-scale reviews of on-land intraplate volcanism have been provided by Weaver and Smith (1989) and Timm et al. (2010), with the latter study also documenting many offshore volcanoes. Chatham Islands volcanism is well-summarised by Panter et al. (2006), although an outstanding question is why this area has repeatedly experienced pulses and long hiatuses of magmatism since the Late Cretaceous. New Zealand’s subantarctic Antipodes Islands (Scott et al. 2013), Campbell Island (Morris 1984), and the Carnley Volcano on the southern Auckland Islands (Gamble et al. 2018) have been synthesised. However, the Antipodes and Campbell Island volcanic centres have extensive but poorly described phreatomagmatic components, and the relationship of Carnley Volcano to the apparently coalescing Ross Volcano in the northern Auckland Islands remains unclear (Scott and Turnbull 2019).

The most comprehensive descriptions of Oligocene to Miocene volcanic fields in Canterbury remain those by Duggan and Reay (1986) and Sewell and Gibson (1988) but these provinces are worthy of more examination since these are unusual in that they have erupted alkaline and sub-alkaline basaltic magmas. This is also true for the North Island Alexandra Volcanic Field (Pittari et al. 2021) and the South Island Waiareka Deborah Volcanic Field and Dunedin Volcanic Group (Scott et al. 2020a, 2020b). The location of Mount Taranaki remains a conundrum since the slab is extremely deep beneath the area, yet the magmatism is apparently arc-related. The best descriptions of Cretaceous to Oligocene volcanic rocks in South Westland remain brief summaries by Sewell and Nathan (1987) and Phillips et al. (2005); these rocks are significant because they were erupted when Westland was still part of the Campbell Plateau ∼480 km to the south and so provide insights into an area of Zealandia that was close to Antarctica. Jurassic-Cretaceous volcanism in Fiordland and Stewart Island has been summarised by Williams (1978), Allibone (1991), Ewing et al. (2007) and Scott et al. (2008), yet the only major isotopic studies of those rocks are oxygen isotope data, which indicate volcanism at very high latitudes (Blattner and Williams 1991).

While this is not the place to review all volcanic research opportunities in Zealandia, it is safe to say that there remain many research directions to pursue; this Special Issue, therefore, provides a platform for future research.

Acknowledgments

I thank all contributors and reviewers of articles for the Special Issue. Fei He and Jasmine Gabrielle-Hinchey from the Royal Society of New Zealand Te Apārangi were instrumental in developing this Special Issue. GNS Science permitted the use of Lloyd Homer images from the Visual Media Library (http://vml.gns.cri.nz). Nick Mortimer, Richard Wysoczanski and an anonymous reviewer are thanked for their comments on this Introduction.

Disclosure statement

No potential conflict of interest was reported by the author(s).