Although analyses of tephra-derived glass shards have been undertaken in New
Zealand for nearly four decades (pioneered by Paul Froggatt), our study is
the first to systematically develop a formal, comprehensive, open-access
reference dataset of glass-shard compositions for New Zealand tephras. These
data will provide an important reference tool for future studies to identify
and correlate tephra deposits and for associated petrological and
magma-related studies within New Zealand and beyond. Here we present the
foundation dataset for TephraNZ, an open-access reference dataset for
selected tephra deposits in New Zealand.
Prominent, rhyolitic, tephra deposits from the Quaternary were identified,
with sample collection targeting original type sites or reference locations
where the tephra's identification is unequivocally known based on
independent dating and/or mineralogical techniques. Glass shards were
extracted from the tephra deposits, and major- and trace-element geochemical
compositions were determined. We discuss in detail the data reduction
process used to obtain the results and propose that future studies follow a
similar protocol in order to gain comparable data. The dataset contains
analyses of glass shards from 23 proximal and 27 distal
tephra samples characterising 45 eruptive episodes ranging from Kaharoa (636 ± 12 cal yr BP) to the Hikuroa Pumice member (2.0 ± 0.6 Ma)
from six or more caldera sources, most from the central Taupō Volcanic
Zone. We report 1385 major-element analyses obtained by electron microprobe
(EMPA), and 590 trace-element analyses obtained by laser ablation
(LA)-ICP-MS, on individual glass shards.
Using principal component analysis (PCA), Euclidean similarity coefficients, and geochemical investigation,
we show that chemical compositions of glass shards from individual eruptions
are commonly distinguished by major elements, especially CaO, TiO2,
K2O, and FeOtt (Na2O+K2O and SiO2/K2O), but not
always. For those tephras with similar glass major-element signatures, some
can be distinguished using trace elements (e.g. HFSEs: Zr, Hf, Nb; LILE: Ba,
Rb; REE: Eu, Tm, Dy, Y, Tb, Gd, Er, Ho, Yb, Sm) and trace-element ratios
(e.g. LILE/HFSE: Ba/Th, Ba/Zr, Rb/Zr; HFSE/HREE: Zr/Y, Zr/Yb, Hf/Y;
LREE/HREE: La/Yb, Ce/Yb).
Geochemistry alone cannot be used to distinguish between glass shards from
the following tephra groups: Taupō (Unit Y in the post-Ōruanui
eruption sequence of Taupō volcano) and Waimihia (Unit S); Poronui (Unit
C) and Karapiti (Unit B); Rotorua and Rerewhakaaitu; and
Kawakawa/Ōruanui, and Okaia. Other characteristics, including
stratigraphic relationships and age, can be used to separate and distinguish
all of these otherwise-similar tephra deposits except Poronui and Karapiti.
Bimodality caused by K2O variability is newly identified in Poihipi and
Tahuna tephras. Using glass-shard compositions, tephra sourced from
Taupō Volcanic Centre (TVC) and Mangakino Volcanic Centre (MgVC) can be
separated using bivariate plots of SiO2/K2O vs.
Na2O+K2O. Glass shards from tephras derived from Kapenga
Volcanic Centre, Rotorua Volcanic Centre, and Whakamaru Volcanic Centre have
similar major- and trace-element chemical compositions to those from the
MgVC, but they can overlap with glass analyses from tephras from Taupō and
Okataina volcanic centres. Specific trace elements and trace-element ratios
have lower variability than the heterogeneous major-element and bimodal
signatures, making them easier to fingerprint geochemically.
Introduction
Tephrochronology is the method by which volcanic ash (tephra) deposits are
used as stratigraphic isochronous marker horizons (isochrons) for
correlating, dating, and synchronising deposits and events in geologic,
paleoenvironmental, and archaeological records (Sarna-Wojcicki, 2000; Shane,
2000; Dugmore et al., 2004; Lowe, 2011; Alloway et al., 2013). In regions
where rates of volcanism are high, and eruptive products are widespread,
tephrochronology is an essential tool in many aspects of geoscience and
associated research (e.g. Hopkins et al., 2021). Geochemical fingerprinting
of the glass shards within the tephra deposits is one of the most common
ways in which tephra is correlated. Traditionally, major elements were used
for correlations (e.g. Westgate and Gorton, 1981; Froggatt, 1983, 1992), but
more recent studies have included minor- and trace-element compositions as
well (e.g. Westgate et al., 1994; Pearce et al., 2002, 2004, 2007; Pearce,
2014; Knott et al., 2007; Allan et al., 2008; Denton and Pearce, 2008;
Turney et al., 2008; Westgate et al., 2008; Kuehn et al., 2009; Hopkins et
al., 2017; Lowe et al., 2017).
Trace elements are more strongly partitioned by fractional crystallisation
processes that occur during the formation of melt and therefore have the
potential to be unique for discrete eruption episodes (e.g. Pearce et al.,
2004). Specifically, a number of key trace elements have been identified as
important for the correlation of rhyolitic tephras, including the high field
strength elements (HFSEs) Zr and Nb; the large ion lithophile elements
(LILEs) Rb, Sr, and Ba; the heavy rare-earth elements (HREEs) Gd, Yb, Sc,
and Y; and the light rare-earth elements (LREEs) La and Nd. Trace-element
ratios are also identified as important, including (1) HFSE/HREE – for
example Zr/Y, Nb/Y, Hf/Y; (2) LILE/HFSE – for example Ba/Th; (3) LREE/HFSE
– for example Ce/Th, La/Nb; (4) LREE/HREE – for example La/Yb, Ce/Yb;
and (5) HFSE/HFSE – for example Zr/Nb, Zr/Th. Some studies have shown that
trace elements and trace-element ratios can distinguish between tephra beds
that have indistinguishable glass-shard major-element signatures and thus
are a robust way of providing accurate correlations (e.g. Westgate et al.,
1994; Pearce et al., 1996, 2002, 2004; Allan et al., 2008; Hopkins et al.,
2017).
Tephra correlation is also increasingly being quantified through statistical
approaches on geochemical data (Lowe et al., 2017), but many of these
approaches (e.g. supervised learning) often require a robust, comprehensive
set of “known” reference data against which to test the analyses of
“unknown” samples. Statistics can also scale data to make them comparable,
but they cannot account or correct for inter-laboratory or historical
variance in analyses. Therefore, incomplete datasets, or datasets
constructed from a range of data sources, will limit the ability to provide
holistic statistical correlations with accurate outputs. Consequently, the
formation of reference datasets that are run in one analytical session, in
one lab, with a consistent methodology is highly desirable for minimising
sources of error. The production of tephra databases is thus being
recognised as an exceptionally useful tool internationally (e.g. Lowe et
al., 2017), made more obtainable with open-access journals and online,
effectively limitless storage, leading to easier publication and maintenance
of large data repositories. Ideally, a global tephra database would exist,
but at present this is beyond the scope and remit of any individual
researcher, research group, or institute(s). Therefore separate, regional
databases for volcanically active (and other) regions are becoming
increasingly popular, such as TephraKam – Kamchatka (Portnyagin et al.,
2020); Tephrabase – Europe (Newton, 1996); AntT tephra database –
Antarctic ice cores (Kurbatov et al., 2014); Alaska Tephra Database
(Wallace, 2018); Klondike goldfields, Yukon (Preece et al., 2011); VOLCORE
– DSDP, ODP, and IODP marine tephra deposits (Mahony et al., 2020). In
addition, in an effort to produce comparable global datasets Abbott et al. (2021) have recently presented guidance for best practices, providing
recommendations and templates for tephra collection, sample preparation, and
physical and geochemical analysis.
Geologic setting
The volcanically active nature of New Zealand (Mortimer and Scott, 2020)
and the longevity and consistency of large-scale rhyolitic eruptions
(Howorth, 1975; Froggatt and Lowe, 1990; Houghton et al., 1995; Wilson et
al., 1995a, 2009; Jurado-Chichay and Walker, 2000; Carter et al., 2003;
Briggs et al., 2005; Wilson and Rowland, 2016; Barker et al., 2021) mean the
landscape currently has a very long, detailed, and complex rhyolitic
tephrostratigraphic framework that is used for a wide range of applications
(Hopkins et al., 2021). However, at present New Zealand tephra studies are
lacking a comprehensive reference dataset resource that has been developed
in a systematic way.
The first large rhyolite-producing eruptions in the Quaternary in New
Zealand were sourced from the Coromandel Volcanic Zone (CVZ) (Carter et al.,
2003; Briggs et al., 2005), including from the Tauranga Volcanic Centre
(TgaVC) from ca. 3.0 to 1.9 Ma (Pittari et al., 2021). At or after
∼ 2 Ma, volcanism moved into the Taupō Volcanic Zone
(TVZ), currently the most active rhyolitic system on Earth (Wilson et al.,
1995a, 2009; Wilson and Rowland, 2016). Nine calderas are recognised within
the TVZ: Mangakino (1.6–1.53 and 1.2–0.9 Ma); Kapenga (0.9–0.7 Ma,
0.3–0.2 Ma, and ∼ 0.06 Ma); Whakamaru (0.35–0.32 Ma);
Reporoa (∼ 0.23 Ma); Rotorua (∼ 0.22 Ma);
Ohakuri (∼ 0.22 Ma); Maroa (0.32–0.013 Ma); Taupō
(0.32–0.0018 Ma); and Okataina (∼ 0.6–0 Ma) (Fig. 1b; Houghton et al., 1995; Wilson et al., 1995a, 2009; Gravely et al.,
2006, 2007; Pittari et al., 2021). The TVZ is further subdivided into the
“old TVZ”, which is defined as being active from inception to the
Whakamaru eruptives (∼ 0.34 Ma), and the “young TVZ”, which
is defined as being active from the Whakamaru eruptives to the present.
“Modern TVZ” is also used to describe the activity since the Rotoiti
eruption (which includes the Rotoiti Ignimbrite, the Rotoehu Ash, and Matahi
Scoria members) ∼ 45–47 ka (Danišík et al., 2012;
Flude and Storey, 2016; Hopkins et al., 2021) to the present (Wilson
et al., 1995a, 2009). In addition to these rhyolitic caldera sources in the
TVZ and CVZ, the peralkaline rhyolitic Tuhua/Mayor Island (MI) volcano
(Fig. 1), forming the Tuhua Volcanic Centre (TuVC) (Froggatt and
Lowe, 1990), is responsible for erupting the Tuhua tephra (7637 ± 100 cal yr BP; Lowe et al., 2019) and at least six other MI-derived tephras
(Shane et al., 2006). The Tuhua tephra is a well-recognised Mid-Holocene
rhyolitic marker horizon within the New Zealand geologic record due to its
distinctive peralkaline geochemistry and mineralogy (Buck et al., 1981; Hogg
and McCraw, 1983; Froggatt and Lowe, 1990; Wilson et al., 1995b; Lowe et al.,
1999; Shane et al., 2006; Hopkins et al., 2021).
New Zealand's climatic setting strongly affects tephra dispersal. The
landmass sits in the path of predominantly westerly to southern-westerly
winds, and therefore the majority of tephra plumes are dispersed to the east
of the volcanic zones (Barker et al., 2019). However, tephra deposits from
these rhyolitic eruptions are found in a range of different environments,
including
marine (e.g. Nelson et al., 1985; Carter et al., 1995; Alloway et al.,
2005; Allan et al., 2008; Lowe, 2014; Hopkins et al., 2020a)
lacustrine (e.g. Lowe, 1988; Shane and Hoverd, 2002; Molloy et al.,
2009; Shane et al., 2013; Hopkins et al., 2015, 2017; Peti et al., 2020,
2021)
wetlands (e.g. Lowe, 1988; Newnham et al., 1995, 2007, 2019; Lowe et
al., 1999, 2013; Gehrels et al., 2006), or
within terrestrially exposed marine or lacustrine sediments, for example
in the
Whanganui Basin (e.g. Seward, 1976; Naish et al., 1996; Pillans et al.,
2005; Rees et al., 2019, 2020),
Wairarapa region (e.g. Shane and Froggatt, 1991; Shane et al., 1995; Nicol
et al., 2002), or
Hawke's Bay region (e.g. Erdman and Kelsey, 1992; Bland et al., 2007;
Orpin et al., 2010;
Hopkins and Seward, 2019) (Fig. 1).
Because of their pervasive nature, high repose period, and high preservation
potential, tephra deposits are a common stratigraphic and chronological aid
in many studies in New Zealand (Shane, 2000; Lowe, 2011; Hopkins et al.,
2021). For example, the eruption of Kaharoa (636 ± 12 cal yr BP, Hogg
et al., 2003) from Mt Tarawera in the Okataina Volcanic Centre (OVC) has
been used to date the arrival of Polynesians in northern New Zealand and map
their expansion and impact across the country (Newnham et al., 1998; Lowe
and Newnham, 2004). The Rerewhakaaitu eruption (17 496 ± 462 cal yr BP; Lowe et al., 2013), sourced from OVC, is used as a marker horizon for
the transition between the last glacial and present interglacial (Newnham et
al., 2003), and several other widespread late Quaternary tephra deposits
form boundaries or key stratigraphic markers in the New Zealand Climate
Event Stratigraphy developed by the NZ-INTIMATE community (e.g.
Kawakawa/Oruanui tephra; Barrell et al., 2013; Lowe et al., 2013).
Compositions of glass and mineral components from rhyolitic tephra deposits
have also been used to reconstruct changes in magmatic systems and give
insight into the complexity of caldera-related eruption episodes (e.g. Smith
et al., 2002, 2005; Cooper et al., 2012; Barker et al., 2016, 2021; Wilson
and Rowland, 2016).
Many of the commonly found rhyolitic tephra horizons in New Zealand are well
studied, dated, and geochemically and mineralogically characterised.
However, often these studies have been eruption-, source-, or
depocentre-specific, and thus only provide a small, effectively piecemeal
catalogue of tephra geochemistry that is not necessarily comparable to those
of other studies. In addition, compositional data are not usually published
in their entirety, or not at all, meaning future studies can neither access nor
use the data for correlation techniques. Furthermore, Lowe et al. (1999)
identified that differing procedural methods employed at different
institutes around New Zealand before and after 1995 produced variable
elemental concentrations for the same tephra (post-1995 SiO2 values
were lower by 0.5 wt %–1.0 wt %, and all other elements had slightly higher
values). Therefore, it is likely that some of the older tephra compositions
that have been relied upon in the past for correlative purposes are no
longer appropriate.
It is therefore timely for a comprehensive, systematic, and accessible New
Zealand tephra database to be established and curated. In this study we
present TephraNZ as a foundation reference dataset of internally
consistent, open-access data for major- and trace-element compositions of
glass shards from a selection of the most pervasive Quaternary tephra
deposits in New Zealand (Table 1). This is by far the most complete
dataset of New Zealand tephra-derived glass-shard compositions published to
date. We discuss in detail the sample preparation, methods of analysis, data
reduction, and data quality control processes used to generate the results
and interrogate the data, thereby providing a template for future studies to
produce comparable datasets. Using the glass-shard data obtained, we present
an overview of the geochemical variability for a range of rhyolitic tephras
of the TVZ; we suggest key geochemical parameters that can be used to
identify the individual tephra layers and apply common statistical
techniques to explore the data. Finally, we propose some future avenues of
study, utilising these data, which would aid in the progression of a formal,
holistic New Zealand tephrostratigraphical framework. Limitations of the
dataset are also considered.
Tephra deposits included in this study. * Jenni L. Hopkins, previously unpublished
data. Age references: (1) Hogg et al. (2003); (2) Hogg et al. (2012); (3) Hogg et
al. (2019); (4) Lowe et al. (2013); (5) Lowe et al. (2019); (6) Vandergoes et al. (2013); (7) Nairn (2002); (8) Howorth (1975); (9) Danišík et al. (2020); (10) Danišík et al. (2012); (11) Bussell and Pillans (1997); (12) Bussell (1986); (13) Pillans (1994); (14) Pillans et al. (1996); (15) Pillans et al. (2005); (16) Rees
et al. (2019); (17) Houghton et al. (1995); (18) Hopkins and Seward (2019) (19) Peti et al. (2021); (20) Pittari et al. (2021); (21) Rees et al. (2020).
Key rhyolitic marker horizons were the focus of our foundation dataset.
Tephras younger than the Rotoehu Ash (together with Rotoiti Ignimbrite; see
Table 1) are generally well recognised in the literature and
commonly used as tephrochronological marker horizons; therefore these were
an obvious choice for the reference dataset. However, for studies using
tephra(s) as marker horizons in older deposits 45 ka–2.0 Ma, there are
limited well-known marker horizons published in the literature. The most
well-studied and accurately dated are those found in the Whanganui Basin
(e.g. Pillans et al., 2005; Pillans, 2017). Although not necessarily “key
marker horizons” yet, these tephras were chosen to be included in this
study for a range of reasons: (1) they are well dated (mostly)
through direct dating techniques; (2) they fall in an important and useful
time window; (3) they are stratigraphically constrained and therefore a
(mostly) chronologically continuous record; (4) they are thick (although
over thickened in some cases) distal deposits and therefore likely represent
dominant (pervasive) horizons in the geologic record; (5) some have been
correlated with offshore deposits (e.g. Alloway et al., 2005; Allan et al.,
2008) or other terrestrial deposits (e.g. Shane and Froggatt, 1991; Shane et
al., 1996; Hopkins and Seward, 2019) and therefore are useful as
geochronological correlatives as we discuss later (Sect. 4.3.2);
and (6) their locations are very well documented and therefore could be used
as tephra type sites or reference sites in future studies.
Known tephra samples in personal collections were collated, prepared, and
reanalysed for this study. Where samples were lacking for key tephra
deposits, their type localities were found, and samples were obtained
through new fieldwork (Fig. 1). Table 1 provides full
details of all the sample locations including their status as either
proximal (0 to tens of kilometres from source) or distal (tens to hundreds of kilometres from source) and GPS
co-ordinates for their exact sampling location. We note here that we have
not attempted to sample multiple tephra beds from a single eruptive episode
in proximal sequences, nor deposits of the same tephra at different
azimuths, as has been undertaken in some more localised or
petrologically focussed studies (e.g. Shane et al., 2005, 2008). We
recognise this limitation but instead have concentrated on analysing a wide
range of pervasive rhyolitic tephras, both proximal and distal, in a
systematic and well-documented way so that future tephrostratigraphic
studies will have a foundation of new, high-quality glass-shard
compositional data for facilitating robust correlations and applications.
Where we have both, we compare proximal and distal analyses of the same
tephra and comment on similarities or differences allowing for an increased
understanding of the variability in the geochemistry seen in the pyroclastic
products of some eruptions. In addition, we have used statistical methods to
demonstrate the integrity of our new datasets (and show how such methods can
enable unknown tephras to be classified).
Sample preparation
Bulk tephra samples were disaggregated in water for 1–5 min in an
ultra-sonic water bath. Clays and ultra-fine sediments (< 5 µm) were
rinsed off, and samples were then wet-sieved using disposable sieve cloths to
125–250 µm or, where necessary, 60–125 µm. Samples were then
dried for 12–24 h at 50 ∘C before mounting in epoxy
resin. Seven samples were mounted into individual drill holes (4 mm
diameter) in 25 mm epoxy round blocks (a 4:1 ratio of EpoTek 301 resin [A]:
hardener [B]). Individual drill holes were then backfilled using the same
epoxy mix (see Lowe, 2011, p. 124, for a schematic illustration). Sample
blocks were polished using the following sequence: ∼ 3 min in
a figure-eight pattern on 800-grit sandpaper with water lubricant to remove
the epoxy and break through to the glass shards, ∼ 1 min on
1200-grit sandpaper with water lubricant to remove any large scratches, and
∼ 1 min on 2500-grit sandpaper with water lubricant to begin to
reveal the outline of the shards. Blocks were then moved on to the diamond
laps with their appropriate lubricant, all at 280 revolutions per minute
rotating the block 90∘ every 30 s followed by 2 min of ultrasonic
bathing at < 24 ∘C between each lap stage to remove
any loose material on the surface of the blocks: ∼ 3 min on 6 µm, ∼ 1 min at 3 µm, and ∼ 1 min
at 1 µm. Blocks were then carbon coated before loading in the
electron microprobe system for analysis.
(a) Map of the North Island, New Zealand, detailing the samples
sites where the reference tephra deposits for the TephraNZ database were
collected. Outlines of CVZ (Coromandel Volcanic Zone) and TVZ (Taupō
Volcanic Zone) are shown by dashed lines. Exact co-ordinates for all sample
sites are detailed in Table 1. (b) Inset, outline shown in (a), the calderas
of TVZ (details from Houghton et al., 1995; Wilson et al., 1995a, 2009;
Gravely et al., 2006, 2007); outline colours of the calderas are used
throughout this article in graphs to link the tephra data with their source
caldera, if known.
EPMA method and data reduction
Major-element analysis of glass shards was undertaken at Victoria University
of Wellington (VUW) by wavelength dispersive X-ray spectroscopy (WDS) on a
JEOL JXA8230 Superprobe electron probe microanalyser (EPMA). Broadly the
method follows that espoused by Kuehn et al. (2011). Backscatter electron
images of each sample were taken and used as block maps to allow the
location of EPMA analyses to be replicated for trace-element analysis. A
defocused circle beam 10 µm in diameter was used at 8 nA and 15 kV to
analyse all major elements as oxides (SiO2, TiO2, Al2O3,
FeOtt, MnO, MgO, CaO, Na2O, K2O) and Cl. Run duration for each
analysis was ∼ 3 min, including online correction. During
standardisation, Na2O was run twice, the second time skipping the peak
search to reduce the volatilisation of the element, with the second
standardisation value then used. Supplement
Table S1.1 (a and b) shows the EPMA set-up and run times (after
Abbott et al., 2021). During the analysis, VG-568 was run as a calibration
standard, and VG-A99 and ATHO-G were run as secondary standards (all
standard data can be found in Supplement Table S3), with two of each
standard (calibration and secondary) analysed between 10 sample analyses to
monitor machine drift (no machine drift was identified).
Initial concentrations were determined using the ZAF correction method, with
secondary offline data reduction undertaken to all samples and standards to
correct for variability in VG-568. Internal correction values were
calculated using the GeoREM reference values of VG-568 from Streck and
Wacaster (2006; Eq. 1) and applied to all the data (Eq. 2). Following this, samples were corrected for deviations from 100 wt %
total; this assumes any variation is due mostly to magmatic water, with a
very small amount of minor and trace elements (Froggatt, 1983; Lowe, 2011)
that are not analysed by the EPMA (Eq. 3). The difference is
reported as “H2OD” in all data tables to allow back calculation
to original data values including totals. Results with H2OD≥ 8 wt % were removed and are listed at the bottom of the table as
“outliers” (Supplement Table 2). Accuracy and analytical precision of the
standards were calculated, where accuracy is the offset from the reference
value for the secondary standards (Eq. 4), and precision is the
standard deviation of all measured secondary standards throughout a run,
reported at 2 standard deviations (SD) to represent a 95 % variability.
internal correction value =average(Xmp/Xrp),
where Xmp= measured concentration of element X of the
calibration standard, and Xrp= reference concentration for
element X of the calibration standard (reference values taken from GeoRem
preferred values http://georem.mpch-mainz.gwdg.de/, last access: June 2021).
corrected data =Xmi/internal correction value,
where Xmi= measured concentration for element X of any sample
or standard.
secondary hydration corrected data =3((corrected data (Eq. 2)/total for that sample)×100)offset from standard (accuracy) =4(absolute value(Xrs-averageXms)),
where Xrs= reference concentration for element
X of the
secondary standard (GeoRem preferred value; MPI-DING; Jochum et al., 2006),
and averageXms= average concentration measured for element X
of all analyses of the secondary standard).
LA-ICP-MS method and data reduction
In situ trace-element analysis was undertaken at VUW using laser-ablation
inductively coupled plasma mass spectrometry (LA-ICP-MS) where a RESOlution
S155-SE 193 nm ArF excimer laser system was coupled with an Agilent 7900
quadrupole ICP-MS. Data for 43 trace elements were acquired using a static
spot method, with a 25 µm spot size, ablation time of 30 s, and
repetition rate of 5 Hz power (method: 10 s background/washout count,
cleaning spot of 25 µm for three laser pulses to clean the glass
shard surface, 20 s background count, 30 s acquisition, 10 s washout; see
Supplement Table S1 for full LA-ICP-MS set-up details; after Abbott et al.,
2021). Synthetic glass standards NIST-612 and NIST-610 were used to tune the
ICP-MS and obtain the P/A factors at a range of spot sizes and laser powers.
During the analysis, a full range of standards was analysed to determine
which produced the most accurate and precise results as a calibration
standard, including NIST-612, NIST-610, BHVO2-G, and ATHO-G. StHS6/80-G was
analysed as a secondary standard throughout (results of which are discussed
below in Sect. 2.5 and shown in Fig. 2 and Supplement Table S5), and all standards (calibration and secondary) were analysed twice
every 10 samples. All data were reduced offline using Iolite v.3™ software (Paton et al., 2011), using 43Ca as the internal standard
value (index channel) and the Trace_ Elements_IS data reduction scheme (DRS). The data
were reduced against ATHO-G as the calibration standard. No post-processing
data reduction was necessary for the trace-element data, but outliers were
removed; precision and accuracy were calculated on STHS6/80-G as described
above (Eq. 4).
Standardisation method
Multiple calibration standards with different trace-element concentrations
were analysed to determine which would be most suitable for trace-element
data reduction. Potential calibration standards included NIST-612, NIST-610,
BHVO2-G, and ATHO-G. These were each run twice every 10 samples, along with
secondary standard STHS6/80-G. Figure 2 shows the STHS6/80-G
results of a range of selected, commonly used trace elements, including Zn
(transition metal), Rb (LILE), Zr (HFSE), La (LREE), and Yb (HREE), normalised
using each of the calibration standards. Overall, the results show that for
the lighter masses (e.g. Zn) there is a large variability in the measured
STHS6/80-G values across the different standards, but all except BHVO2-G sit
within error (2 SD) of the reference value (Fig. 2). For the
heavier masses (e.g. La, Yb, Fig. 2), the variation from the
reference value observed within the analysed values decreases, except for
NIST-610, which remains highly variable in the middle masses (Rb, Zr,
Fig. 2), with variability reducing in the heavier masses. The data
show that the use of ATHO-G as the calibration standard (for data reduction
of rhyolites) produces the most accurate and precise data for the secondary
standard, for all except the elements with the heaviest masses and smallest
concentrations (e.g. Yb).
Statistical methodsPrincipal component analysis
To visualise elements that distinguish the different tephra compositions we
have used principal component analysis (PCA). PCA was run in the coding
platform R (R core team, 2019) v3.6.2 and RStudio v.1.2.5033 using packages
“ggbiplot” (Vu, 2011), “Hotelling” (Curran, 2018), “ggplot2” (Wickham,
2016), “factoextra” (Kassambara and Mundt, 2020) and “vegan” (Oksanen et
al., 2019). Data for Tuhua tephra were removed as these would unnecessarily
skew the results due to their distinct geochemistry. Non-normalised,
average, elemental values were used from each tephra sample, for example Si
(in ppm), no oxide values, no ratios (e.g. SiO2/K2O), or sums (e.g.
Na2O+K2O). All element values were centred using a centred
log-ratio transform to deal with closure effect (clr: column mean subtracted
from each value) and scaled (value divided by the standard deviation of the
column) to compare elements with concentrations that differ by orders of
magnitude. PCA was run using the “prcomp” (Venables and Ripley, 2002)
function, and PCA contributions were calculated using “fviz_contrib” (Kassambara and Mundt, 2020) function. A template of the coding
script used can be found in Supplement Material 1.
Compilation of trace-element standard data produced during the
first run of glass-shard analyses. These data show selected element
concentrations of secondary standard STHs6/80 normalised using difference
calibration standards (NIST-612 – orange; NIST-610 – green, ATHO-G –
blue, and BHVO2-G – red). The grey shaded area shows the preferred GeoREM
reference value (http://georem.mpch-mainz.gwdg.de, last access: June 2021) error
margin reported for each element for STHS6/80. Note that for standard
NIST610, two data points were removed as outliers; full data can be found in
Table S5.
Average and standard deviation values (shown in italics) for glass-shard analysis of
major and trace elements. Full data can be found in the Supplement
Table S2. P – proximal; D – distal, K – Kaipo Bog sample;
XXX – Pillans et al. (2005) sample number; n= number of shards analysed
(trace number in parentheses); H2OD* water and volatile calculated
by difference.
To identify the tephra samples that were most similar, and could therefore
pose problems in attempting to obtain unique fingerprinting, we ran
Euclidean similarity coefficient (ESC) analysis. ESC was run in R and
RStudio using the package “stats” (R core team, 2019). Following the
guidelines of Hunt et al. (1995) for ESC analysis, we used non-normalised,
mean concentrations of the elements highlighted by the PCA to be the most
indicative of variance in the dataset. These values were input as comparison
values, and the function “as.matrix.dist” was used to run the
“Euclidean” distance measure. This method calculates the similarity of
samples based on an infinite number of comparison input values. A template
of the coding script used can be found in Supplement Material 2.
The output table was manipulated post-production to provide the colour
formatting.
Results
The averages and their standard deviations for all samples are reported in
Table 2; the full reference dataset can be found in Supplement Table S2. All reported values in the text and figures (unless stated
otherwise) are recalculated (normalised) to 100 % on a volatile-free basis
(following Lowe et al., 2017) with the difference between the raw total and
100 % being reported as “H2OD” (Table 2). For best
correlation results, we recommend that the full dataset is used in order to
see the trends in the geochemical data rather than just the means and
standard deviations.
Data quality
Standard values for VG-568 and VG-A99 are taken from the GeoREM. The
reference values used as a standard (by other publications) are from
Jarosewich et al. (1980). However, for the purpose of this research we have
chosen alternate values published by Streck and Wacaster (2006). A
comparison of the reference values from both publications is shown in
Supplement Table S6 and Fig. S6.1. Most of the values reported
are within error of one another for both VG-568 and VG-A99. However, the
dataset from Streck and Wacaster (2006) is more complete including values
for MgO and Cl, which are not reported by Jarosewich et al. (1980). We do
note, however, that Cl is challenging to analyse accurately on EPMA for
glass due to its low concentration and especially as there are few standards
that have similar compositions (e.g. Jochum et al., 2006). Our samples have
between 0.3 wt % and 0.06 wt % Cl; therefore, VG-568 (with Cl = 0.1 wt %),
ATHOG (with 0.04 wt %), and VG-A99 (with 0.02 wt %) attempt to provide a
good range for standard comparison.
Figures plotted in Supplement Table S3 (Figs. S3.2, S3.3, and S3.4) show the
variability in the concentrations analysed by the EPMA of the standard data
throughout the running of these samples. For the secondary standards ATHO-G
(Fig. S3.3) and VG-A99 (Fig. S3.4), there
is some clear variability within the batches of samples run. For example for
SiO2 for ATHO at point 60, there is a clear jump in the values
reported, for Na2O for ATHO at points 92–101 there are some very low
concentrations, and for MgO for VG-A99 there are clear variations in
different run sets. The variation observed in all these data is likely due
to a number of factors including (1) a change to a different standard shard
during the run; (2) re-calibration of the EPMA after a period of down time
(note the dates of analyses) and/or (3) day-to-day variations in machine
performance; (4) for the case of Na2O, possible volatilisation of
Na2O due to repeated analysis of the same standard shard; (5) use of an
inappropriate primary calibration standard (for example a rhyolite standard
(VG568) to calibrate a basaltic glass (VG-A99) which is used in this case as
a secondary standard).
Recently, a number of studies have reported difficulty in accurate analysis of Na2O concentrations in reference standard ATHO-G: (1) a large range of values are reported from different analytical techniques (3.53 wt %–4.31 wt %, Jochum et al., 2006), and (2) the reported reference value for ATHO-G from Jochum et al. (2006) is too low (reported as 3.75 wt %; e.g. Lowe et al., 2017; Portnyagin et al., 2020). Our use of Steck
and Wacaster (2006) reference data for VG-568 as an internal calibration
(3.52 wt %) rather than the Jarosewich et al. (1980) value (3.75 wt %)
brings our secondary standard data in alignment with the original Jochum et
al. (2006) values for ATHO-G (see Supplement Table S3.3). However, it is possible that because
of this, our sample values reported for Na2O are too low. Further
studies into this community-wide issue will hopefully allow this discrepancy
to be resolved.
During LA-ICP-MS tuning oxide production was monitored using the ThO / Th
ratio, and this value was tuned to between 1.3 % and 1.8 %, which is
considered high by current standards (e.g. Portnyagin et al., 2020, reported
values of 0.5 %–0.7 %), but is comparable with values in older studies
(e.g. Jochum et al., 2006, report values “< 1 %–2 %”; Pearce et
al., 2011, reported values “typically ∼ 1.5 %”; Allan et
al., 2008, reported values “typically < 1 %, always < 2 %”). This high oxide production value could have had impacts on some
elements. For example, it is likely that there was a high addition of SiO
into our analyses; SiO can interfere with 45Sc, or alternatively, BaO
can interfere with 153Eu. However, because the concentration of
SiO2 in our samples is similar to that of our secondary standard
(ATHO-G), the data should still be viable. In addition, to monitor the
impact of oxides on our elements we analyse and report multiple isotopes of
Sr (86 and 88), Zr (90 and 91), Mo (95 and 98), Ba (137 and 138), and Eu
(151 and 153). The concentrations of these elements do not show significant
variability (e.g. Figs. S6.2.3, and 6.2.4; RSr2=0.96, RZr2=0.99). In addition, when plotted together, Ba vs.
153Eu shows no relationship (Fig. S6.2.5), proving
little-to-no oxide interference has impacted the values obtained for these
elements.
Ti, Mn, Ca, and Si were analysed by both EPMA and LA-ICP-MS: Fig. S6.2.1 (Ti) and Fig. S6.2.2 (Mn) show comparative analyses of
concentrations measured on the same spots for EPMA vs. LA-ICP-MS. For Ti,
R2=0.63, suggesting a good agreement between the two methods of
analysis. Any anomalous values are indicative of mineral contamination in
the LA-ICP-MS analysis (potentially orthopyroxene or titanomagnetite). For
Mn, the R2=0.26, showing a poor agreement between the two analysis
types. However, this result is likely due to the imprecision afforded by the
EPMA analysis on such small concentrations. For future analyses, to allow a
full comparison of the elements between the two methods and therefore
identification of contamination in the LA-ICP-MS analyses, Portnyagin et al. (2020) suggest analysis of all major elements by LA-ICP-MS.
Major-element results
All glass shards analysed are characterised as rhyolitic according to the
classification of Le Maitre (1984) (Fig. 3), with SiO2
concentrations (normalised) ranging from 72.5 wt % to 79.8 wt % (with
the majority 74 wt %–79 wt %), and Na2O+K2O ranging from 5.8 wt % to 9.8 wt %. Three compositional regions with high concentrations
of samples are evident within Fig. 3. These show a negative trend
between SiO2 and Na2O+K2O, with each region separated by
differing SiO2 values – for example, SiO2=76 wt %–77 wt %,
77.5 wt %–78 wt %, and 78 wt %–79 wt %. Glass samples from the peralkaline Tuhua
tephra (TuVC) are identifiable because of their unique (peralkaline)
geochemistry, with much higher Na2O+K2O (≥ 9 wt %) for
equivalent SiO2(=73.5 wt %–75 wt %; Lowe, 1988) in comparison to
those of the rhyolitic TVZ-sourced deposits (Na2O+K2O ≤ 8.5 wt %). Tuhua-tephra-derived glasses also have higher FeOt (≥ 5.6 wt %) and Na2O (≥ 4.7 wt %) but lower CaO (≤ 0.8) and
Al2O3(≤ 10.1) in comparison to the analyses for the rest of
the samples (FeOt= 0.2 wt %–2.8 wt %, Na2O = 2.6 wt %–5.1 wt %, CaO =
0.5 wt %–2.6 wt %, and Al2O3= 11.8 wt %–15.2 wt %; Fig. 4). For all other major elements, the compositional variation of the Tuhua
tephra samples sits within the overall range for the other samples, with
TiO2=0.02 wt %–0.55 wt %, MnO = 0.01 wt %–0.2 wt %, MgO = 0.01 wt %–0.63 wt %, K2O = 1.8 wt %–6.0 wt %, and Cl = 0.01 wt %–0.72 wt %
(Fig. 4).
Of the 45 tephra samples, 22 have a “homogeneous signature”, homogeneity
being defined here (as an approximation) when the standard deviation of the
sample is equal to or less than analytical error (2 SD of secondary standard:
for example, for FeOt=± 0.23 wt %, CaO =± 0.10 wt %). The majority (∼ 64 %) of the samples that have a
homogeneous signature are from OVC (e.g. Whakatāne, Mamaku, Rotoma) or from
calderas older than OVC (∼ 32 %), such as (1) Upper Griffins
Road tephra, a correlative of the Whakamaru eruptives, Whakamaru Volcanic
Centre (WVC), and (2) Mangapipi tephra, a correlative to deposits of
Mangakino Volcanic Centre (MgVC; Fig. 5a). Ten samples show a
heterogeneous signature (where standard deviations for both FeOt and CaO are
greater than analytical errors), with most from a proximal source
(∼ 30 %), or from tephras deposited in the Whanganui Basin
area (40 %), and with the remainder being from the Mangaone Subgroup
eruptives from the OVC: Hauparu, Maketū, and Ngāmotu (Fig. 5b).
Glass shards from four tephra samples show a bimodal signature in some major
and trace elements, where specific elements split the populations into two
distinct groups. Tephras showing this phenomenon include Rotorua (OVC),
Rerewhakaaitu (OVC), Poihipi (TVC), and Tahuna (TVC). The bimodal signatures
of Rerewhakaaitu and Rotorua are well documented (Shane et al., 2008),
whereas those of Poihipi and Tahuna are newly identified here (Fig. 6). All four of these tephra horizons have their glass-shard bimodal
signatures produced predominantly by K2O concentrations, into high
(≥ 3.8 wt %) and low (≤ 3.6 wt %) populations (Fig. 6) linked to the crystallisation of biotite minerals. This relationship has
been discussed in previous research (for Rerewhakaaitu and Rotorua) and
modelled as two different biotite populations formed through fractional
crystallisation in a zoned magma chamber (e.g. Shane et al., 2003; Nairn et
al., 2004), resulting in the formation of heterogeneity in the magma and
hence the formation of different glass compositions.
For five of the tephras, we undertook analyses on glass from both proximal
and distal samples. These tephras included Whakatāne, Rotoma, Waiohau,
Rotorua, and Rerewhakaaitu, which are all derived from OVC (Table 1). For Rotoma, Rerewhakaaitu, and Waiohau, the signatures of the proximal
and distal deposits are indistinguishable, whereas for Whakatāne and Rotorua
the proximal signature is highly variable, and the distal signature is
homogeneous but overlapping with part of the extent of the proximal
signature (e.g. Fig. 7). Similar findings are reported and
discussed in more detail for Whakatāne tephra in Kobayshi et al. (2005) and
Holt et al. (2011) and for Rotorua tephra in Shane et al. (2003a) and
Kilgour and Smith (2008).
Trace-element results
Figure 8 shows a primitive mantle-normalised spider plot of all the
trace-element data for the glass shards analysed (after McDonough and Sun,
1995). The majority of the data plot along a common pattern of variable
concentrations of HFSE, LILEs, and LREEs, but they show more consistent
concentrations of HREEs (Gd to Lu). Of note are peaks in Nd, a negative Sr
anomaly relative to LREE, and a positive Zr–Hf anomaly relative to Sm. Sr
and Ba show the largest variability in concentrations that is likely caused
by a variability in feldspar crystallisation (Pearce et al., 2004). Several
different patterns are observable within this full data suite pertaining to
individual samples. The obviously different signature is that for glass from
Tuhua tephra, which shows a low concentration of Ba (< 10 ppm) and Sr
(< 1 ppm) in comparison with values for the rest of the samples, and
with high concentrations of all other elements, especially the REEs
(Fig. 8). Analyses of glass shards from the Maketū tephra can also
be identified by their high concentrations of all elements in comparison to
the TVZ trends but mid-range Nb values (between those of Tuhua and the
general trend) (Fig. 8). We also note Er and Lu peaks, which
pertain to glasses from the Te Rere tephra, that sit at the higher
concentration levels of the general trend (these could potentially be
analytical artefacts; Fig. 8; Table 2) and samples from Ngāmotu,
Rotoehu/Rotoiti, and Earthquake Flat deposits that sit at the lower overall
trace-element concentration levels of the general trend (Fig. 8).
For the tephras where both proximal and distal samples of glass have been
analysed for trace elements, the HFSEs (including Zr, Hf, Th, and Ti) and
LILEs (including Rb, Sr, and Cs) may exhibit heterogeneity between the
proximal and distal samples, whereas the HREE and the LREE tend to have a
lower variability (Fig. 7).
Total alkali (Na2O+K2O) vs. SiO2 (TAS) plot for
glass compositions for all reference data (presented on a normalised basis).
Identified and highlighted by blue dashed outline are the glass-shard
compositions for the Tuhua tephra (Mayor Island; MI), and highlighted by the
red dashed outlines are the regions on the TAS diagram that show the highest
density of samples. The inset shows a full TAS diagram (always on an
anhydrous basis) to provide context for the enlarged figure. Regions of the
TAS diagram follow the nomenclature of Le Maitre (1984): A – andesite, B –
basalt, Ba – basanite, BA – basaltic andesite, BT – basalt–trachyte, D
– dacite, P – phonolite, PB – picrobasalt, PT – phonotephrite, R –
rhyolite, T – trachyte, TA – trachyandesite, TB – trachybasalt, TP –
tephriphonolite.
Major-element bivariate plots of glass-shard compositions for all
reference data (presented on a normalised basis). Highlighted in the insets
by blue dashed lines are the Tuhua tephra samples. These are removed from
the enlarged figure to allow the detail of the majority of the samples to be
seen more clearly. Total iron expressed as FeO.
Examples of major-element bivariate plots for glass-shard analyses
of tephras (presented on a normalised basis) which show (a) homogeneous
signatures, where the standard deviation of the analysis is less than the
analytical error (shown as 2σ), and (b) heterogeneous signatures,
where the standard deviation of the analysis is greater than the analytical
error. Different colours indicate the differing caldera sources (shown in
Fig. 1), and different symbols show the different tephras. P – proximal
sample (see Table 1). Total iron is expressed as FeO.
Selected major-element biplots of glass analyses (presented on a
normalised basis) of samples from Poihipi and Tahuna tephras (both TVC
sourced) that exhibit a bimodal signature. This bimodality is identified as
being caused by K2O concentration (e.g. see Lowe et al., 2008; Shane et
al., 2008), and therefore plots with other elements (major or trace) do not
show this bimodality. Total iron is expressed as FeO.
Major- and trace-element biplots showing the glass-shard-derived
geochemical relationship of Rotorua (OVC) proximal (P) and distal (D) tephra
deposits (presented on a normalised basis, total iron expressed as FeO).
Distal deposits may have a signature with lower geochemical variability
which overlaps within the spread of the heterogeneous proximal signatures.
This variation can often be resolved by using trace-element plots of
selected elements – see text for discussion.
Primitive mantle normalised (McDonough and Sun, 1995) trace-element
spider plot for glass analyses for all reference samples. Highlighted are
key elements discussed in the text coloured by their characteristics
including HFSE, LILE, LREE, and HREE. The full plot is presented to show the
density of data with the dominant trend line plus the obvious deviations
from this. The samples which correspond to these deviations are shown in the
smaller plots at right, including analyses on glass from Tuhua (MI), Maketū,
Te Rere, and Rotoehu (OVC) tephras. The Rotoehu Ash signature is also
similar to that for the Rotoiti Ignimbrite (which are coeval deposits;
Nairn and Kohn, 1973), the Earthquake Flat tephra (Kapenga VC; Nairn and Kohn, 1973),
and the Ngāmotu tephra (OVC; Jurado-Chichay and Walker, 2000).
DiscussionDistinguishing geochemical characteristicsMajor and trace elements in general
In many cases, the major-element concentrations in glass are sufficient to
allow different tephras to be distinguished (including through the common
use of biplots), a result consistent with the findings from much previous
work both in New Zealand and elsewhere (e.g. Lowe et al., 2017). However,
previous studies have also shown that for some New Zealand tephras more
elements from the glass analyses are often required to distinguish between
tephras from different eruptions. For this reason we used principal
component analysis (PCA) on the dataset to compare multidimensional data
rather than an array of traditional biplots. Looking at data in a
multidimensional space can allow variations to be more readily distinguished
and visualised because all constituent elements are used, not just two.
PCA results for the glass-shard major elements (Fig. 9) show that
PC1 and PC2 explain 82.7 % of the variance within the data. Al, K, Si, Na,
and Ti make the highest contributions to PC1 (Fig. 9), while Fe,
Mn, and Cl have the greatest loadings on PC2 (Fig. 9); therefore,
these elements are most appropriate for distinguishing between tephra
deposits for the reference dataset as a whole (Fig. 9). These major
elements, especially Fe and K (±Ca), have long been recognised as
being useful to distinguish many New Zealand late Quaternary tephras from
one another (e.g. Lowe, 1988; Shane, 2000; Alloway et al., 2013); however,
the inclusion of Ti, Al, Mn, and Cl is somewhat unusual. In a number
of cases (discussed below), however, major-element concentrations are shown
to overlap for certain tephra horizons, and thus trace elements and trace-element ratios are investigated to provide additional variables to use as
discriminants. PCA was also applied to scaled trace elements and major
elements together, with the results indicating that PC1 and PC2 could
explain 62.8 % of the variability in the full data suite with V, Co, Mg,
Cu, Ti, Sr, Sc, Ca, Cs, and Zr being the 10 highest contributors to PC1
and Cu, Mn, Mg, Cs, Sc, Co, Ti, Sr, Th, and Rb highlighted as the 10
highest to PC2 (Fig. 10). Therefore, these elements, and the ratios
of these elements, have the highest potential to distinguish individual
tephra horizons when using their glass-shard compositions alone.
Results of PCA analysis on all TephraNZ major-element reference data for glass (normalised). Data
are scaled to allow comparison within the PCA analysis. Tephra samples are coloured as per their source centre,
and ellipses highlight the mean compositional region for each source caldera (KVC – Kapenga Volcanic
Centre, MgVC – Mangakino Volcanic Centre, OVC – Okataina Volcanic Centre, RoVC – Rotorua Volcanic
Centre, TVC – Taupō Volcanic Centre, and WVC – Whakamaru Volcanic Centre). PCA analysis was performed
in R (see Supplement 1 for R script). Bar plots highlight the top elemental contributions for PC1 and PC2. The red
dashed lines on the elemental contribution plots indicate the expected average contribution; if the contribution
by each element were uniform, the expected value would be 1/no. of variables (e.g. 1/9=∼11 %). Therefore, a
variable with a contribution larger than this cut-off line (∼11 %) is considered important in contributing to
the component.
Results of PCA on all TephraNZ reference data for glass. Data are
scaled to allow comparison within the PCA analysis. Tephra samples are
coloured as per their source centre (see key in Fig. 9). Mean ellipses have
been removed for clarity for this figure. PCA analysis was performed in R
(see Supplement 1 for R script). Bar plots highlight the top elemental contributions
for PC1 and PC2. The red dashed line on the elemental contribution plots
indicates the expected average contribution; a variable with a contribution
larger than this cut-off line is considered important in contributing to
the component.
Major-element biplots to distinguish between caldera sources of
tephras based on their glass major-element compositions (presented on a
normalised basis; total iron is expressed as FeO): (a) and (b) show a
comparison between all glass-shard analyses for the TVC- and MgVC-sourced
tephras; (c) and (d) indicate the distinction in glass compositional
signature for the eruptives from the OVC and TVC that post-date the
Kawakawa/Oruanui (KOT) eruption; (e) and (f) plots distinguish the glass
analyses for tephra from the OVC into component eruptive time periods, with
tephra from the Mangaone Subgroup (Jurado-Chichay and Walker, 2000; Smith et
al., 2002) distinguishable from all other tephra from the OVC; (g) and (h)
show the similarity in the geochemical compositions of glass of the tephras
from the OVC and TVC for the eruptions prior to, and including, the KOT
eruption. Colours are consistent for each caldera source; symbols are
representative of different groups of tephra defined in the keys for each
set of plots.
Source-specific major and trace elements
The central TVZ contains nine recognised calderas, each with different
eruption histories but all having produced large-magnitude/volume
tephra-producing rhyolitic eruptives. Some of the calderas are attributed to
single caldera collapse events (Rotorua, Reporoa, and Ohakuri), whereas
others represent composite collapse events that overlap spatially but not
temporally (Mangakino and Kapenga). However, the majority reflect multiple
collapse events over an extended period of time (Maroa, Okataina, Taupō,
and Whakamaru) (Fig. 1; Wilson et al., 1995a, 2009; Barker et al.,
2021). Although the calderas are mostly discrete in space, evidence from
multiple eruptions has shown their plumbing systems may be linked
tectonically (e.g. Wilson et al., 2009; Allan et al., 2012). Hence, the
ability to trace a tephra deposit to a caldera source through glass-shard
geochemistry alone could be challenging.
The results of the PCA analysis suggest that tephra sourced from the TVC can
be distinguished from those of a proposed Mangakino source (MgVC)
(Fig. 9). Using SiO2/K2O vs. Na2O+K2O, the
glass shards of the TVC tephras generally have higher SiO2/K2O and
lower Na2O+K2O in comparison to those of the equivalent oxides
for MgVC-sourced tephra (Fig. 11a). This information is important,
but because of the large age differences for the calderas (TVC
∼ 0.32 Ma to present, and MgVC ∼ 1.6 to 1.53 Ma and ∼ 1.2 to 0.95 Ma), the use of this distinction is
likely more important for discussions on mantle source dynamics rather than
for geochemical correlation of tephra deposits.
Previous studies have suggested that the geochemical characteristics of
glass shards from TVC and OVC tephra deposits post-dating the eruption of
the Kawakawa/Oruanui (KOT) can be distinguished using fO2 of Fe–Ti
oxides and minerals (Shane, 1998), pumice and lava compositions (Sutton et
al., 2000), and glass chemistry (Stokes et al., 1992). Our results also show
there is a bimodality in the TVC glass-shard data as a whole and that the
post-KOT tephra deposits from the TVC and OVC are quite different, whereas
the pre-KOT tephras from OVC and TVC are similar (Fig. 11c and d).
Most glass shards erupted after the KOT event from the TVC have low
SiO2 (≤ 77 wt %), less variable K2O (∼ 3 wt %), and higher values for all other major elements in comparison
with those of the glass shards erupted from the OVC (Fig. 11c and d). In contrast, tephras erupted from the TVC and OVC prior to, and
including the KOT, do show a large amount of overlap in their glass
geochemical signatures. For OVC (Fig. 11e and f), there is a high
density of samples that have their SiO2 concentrations at
∼ 78 wt %; however, there is a high variability in
SiO2 overall, with Maketū, Hauparu, and Ngāmotu of the Mangaone
Subgroup plotting with SiO2 concentrations ≤∼ 76 wt % and the remaining Mangaone Subgroup samples (Unit L, Awakeri, and
Mangaone) clustering at SiO2=76 wt %–77.5 wt % (FeOt=∼ 1.2 wt %, K2O =∼ 2.8 wt %,
Al2O3=∼ 13 wt %, CaO =∼ 1.2 wt %), a finding consistent with those of Smith et al. (2005), who divided
the Mangaone Subgroup into “old” and “young” eruptives on the basis of low
and high SiO2, respectively, unlike the other OVC-sourced samples that
plot around SiO2=∼ 77.5 wt %–79 wt %, (FeOt=∼ 0.8 wt %–0.9 wt %, K2O = 2.75 wt %–4.5 wt %,
Al2O3=∼ 12 wt %–13 wt %, CaO =∼ 0.5 wt %–1.0 wt %; Fig. 11c and d). Analyses from the Rotoehu/Rotoiti
tephra deposits plot independently from those of other OVC eruptives for
this time period. However, they overlap with those of some
TVC-tephra-derived glass compositions (Poihipi, Tahuna, Okaia, and KOT). The
Rotoehu/Rotoiti tephra deposits have a markedly homogeneous geochemical
signature and are also much older than TVC eruptions (Table 1).
Hence, coupled with the thickness of the deposits, it is likely that a
tephra linked to the Rotoehu/Rotoiti eruption would be obvious to
distinguish through stratigraphic relationships and age combined with the
geochemistry.
The TephraNZ dataset presented here also includes analyses of glass of
samples from tephras erupted from the Kapenga Volcanic Centre (KVC;
Earthquake Flat eruption), Rotorua Volcanic Centre (RoVC; Ararātā Gully and
Kākāriki), and Whakamaru Volcanic Centre (WVC; Fordell, Upper and Lower
Griffins Road, Potaka, Rewa, Pakihikura, and Mangapipi). In addition, some
older tephra deposits have been recorded in the Whanganui Basin and
elsewhere. These are well-known beds, but their caldera sources are not yet
defined (Alloway et al., 1993; Pillans et al., 1994, 2005; Shane et al.,
1996; Rees et al., 2018, 2019, 2020). Figure 12 shows a plot for
the data from KVC, RoVC, and WVC with those regions populated by glass data
from samples from the OVC, TVC, and MgVC sources. Overall, the samples plot
with a lower SiO2/K2O ratio (≤∼ 25) similar to
that of the MgVC-sourced tephra, which seems to be indicative of samples
from older sources in comparison with those from the OVC and TVC. The
samples potentially linked to RoVC (Bussell, 1986; Bussell and Pillans,
1997) show different geochemical compositions. For example,
Kākāriki-tephra-derived glass has slightly higher SiO2≥78 wt %) in comparison to that of the Ararātā Gully tephra (SiO2≤77 wt %), suggesting that they are likely derived from different
eruptions but potentially the same source (Mamaku Ignimbrite reportedly has
variable geochemical phases; Milner et al., 2003). Glass from the KVC sample
(Earthquake Flat tephra) has a very homogeneous signature in the major
elements but a more variable signature in the trace elements, both of which
overlap with OVC- and TVC-source signatures. There is a very large spread
for the data from the unknown samples, precluding the ability to specify
their source based simply on major and trace elements alone. Nevertheless,
their glass compositional signatures are more similar to those of the older
MgVC-sourced tephra, in comparison to those of the younger TVC and OVC
deposits, as would be expected based on their known age range (Table 1).
Major- and trace-element biplots of indicative elements in glass
to show the relationships between the tephras from Mangakino Volcanic Centre
(MgVC – orange shaded regions), Taupō Volcanic Centre (TVC – red
shaded regions), and Okataina Volcanic Centre (OVC – blue shaded regions),
and the tephras from known and unknown sources within the TephraNZ data
base.
Homogeneous, heterogeneous, and bimodal samples
Fingerprinting of glass shards for correlation relies on the ability to
distinguish between different deposits, and therefore a homogeneous signature
for a single eruptive that is distinct from all other samples is the ideal
“fingerprint”. However, sometimes there is more complexity in the
geochemical data, and heterogeneity can develop in a tephra deposit through a
number of mechanisms including the following (Lowe, 2011):
variability in the magma body itself (e.g. Nairn, 1992; Nairn et al., 2004;
Smith et al., 2004; Kobayashi et al., 2005; Shane et al., 2008; Charlier and
Wilson, 2010; Klemetti et al., 2011; Cole et al., 2014)
proximal versus distal complexity, linked to (1) (e.g. Manning, 1996; Shane
et al., 2003a; Holt et al., 2011)
post- or syn-depositional reworking (e.g. Schneider et al., 2001).
For example, the heterogeneous signature identified for glass from the
Kaharoa tephra agrees with previous findings for this eruptive. Nairn et al. (2004) and Sahetapy-Engel et al. (2014) reported that glass compositional
variability within the Kaharoa deposits shows sequential tapping of a
stratified magma body coupled with syn-eruptive changes in dispersal
patterns. In general, this is likely one of the reasons why some of the
proximal tephra deposits analysed in this study have a more variable
geochemical signature in comparison to those of their distal counterparts
(Fig. 7). Although the proximal deposits record the detail in the
eruption progression, the distal deposits tend to record the very largest
phase of the eruption (e.g. Walker, 1980), but differences can be expected
to occur also according to the azimuths of wind direction during an eruption
and the number and degree of interconnectedness of magma bodies involved in
the eruption (e.g. Walker, 1981; Kilgour and Smith, 2008; Sahetapy-Engel et
al., 2014; Storm et al., 2014; Rubin et al., 2016).
The tephrochronological principle is much more likely to utilise distal
unknown deposits, and therefore we suggest that using the distal signature
(or signatures) may be more appropriate for correlation in many studies. In
general, distal tephras are more chemically homogeneous – but with some
notable and well-documented exceptions – and this attribute therefore
allows them to be traced over large areas (Manning, 1996). Alternatively,
the identification of heterogeneity or bimodality in distal tephras, once
recognised, can be an additional useful characteristic for fingerprinting
(e.g. Shane et al., 2003a, 2008; Lowe et al., 2017). These statements,
however, rely on the tephra being identified as a primary deposit, and not
reworked. Reworking is commonly seen in paleofluvial deposits, for example
those in the Whanganui Basin, and in other environments thin tephras are
prone to mixing such as in surficial soils. This reworking can mix tephra
from multiple eruptions and can cause highly variable glass chemistry
within a single deposit (e.g. Shane et al., 2005, 2006). Fluvial reworking
can be commonly identified by sedimentary structures within the deposit, for
example, ripples or cross bedding indicative of fluvial transport and
deposition (e.g. Shane, 1994; Schneider et al., 2001), over thickening of
deposits (e.g. Vucetich and Pullar, 1969; Lowe, 2011), or through shard
morphology, for example anomalously large shards or rounding of shards (e.g.
Leahy, 1997).
Heterogeneous signatures (defined in approximation of where the standard
deviation of the analyses is greater than the analytical error) in major-element compositions were identified for 10 of the tephra deposits:
Kaharoa, Taupō Y5 proximal (P), Whakatāne-P, Hauparu, Maketū, Ngāmotu,
Fordell, Onepuhi, Birdgrove, and Ototoka. Our data show that for some
samples, specific trace elements and trace-element ratios have lower
geochemical variability (Fig. 13a). The elements that work best to
separate out the individual units within a deposit with a heterogeneous
signature reflect the minerals that have formed during fractional
crystallisation of the melt. Because of this, different elements or element
ratios work for different tephras. For example, for glass from Kaharoa, Sr
exhibits little variability (27–79 ppm), whereas for glass from Taupō,
Sr compositional range exemplifies the heterogeneity in the sample (62–158 ppm; Fig. 13a).
Bimodality was identified for glass shards derived from four of the tephra
horizons analysed: Rotorua (OVC), Rerewhakaaitu (OVC), Poihipi (TVC), and
Tahuna (TVC). For all four of these, K2O concentration in glass
exhibits bimodality, and therefore trace elements with similar chemical
properties reinforce the bimodality (for example, LILEs Rb, Sr, and Cs;
HFSEs Zr, or REE Eu), whereas most other trace elements do not show this
bimodal signature (Fig. 13b).
Indistinguishable tephras
Euclidean similarity coefficient (ESC) analysis was used on all glass-shard
reference data for tephras from Rotoiti/Rotoehu to Kaharoa in addition to
the PCA and geochemical investigation to determine those samples that have
indistinguishable element concentrations at similar ages (Table 3).
Table 3a shows that similarities (similarity coefficient values
(SC)) are observed in the major-element signatures of glass analyses for the
following tephras: Waimihia and Unit K (SC = 0.11); Rotoma-P and
Whakatāne-D (SC = 0.18); Mamaku and Rotoma-P, Rotoma-D (SC = 0.19 and 0.2,
respectively); Poihipi and Rotoma-P (SC = 0.18); Rotoiti/Rotoehu and
Rotoma-D (SC = 0.13); Te Rere and Rerewhakaaitu (SC = 0.16); Tahuna and
Rotoma-P (SC = 0.19); KOT and Okaia (SC = 0.11); KOT and Unit L (SC =
0.21); and Poihipi and Tahuna (SC = 0.18). When the key trace element are
analysed (of the eruptions identified as having similar major elements;
Table 3b), Waimihia and Unit K (SC = 8.88), Whakatāne and
Rotoma (SC = 7.79), Poihipi and Tahuna (SC = 4.24), KOT and Okaia (SC
= 4.25), and KOT and Unit L (SC = 8.44) come up with significantly low
(< 10) similarity coefficients for trace elements also, hence
suggesting these samples will be indistinguishable in both major and trace
elements. In addition, when simple geochemical assessment is applied,
similarities are observed between glass analyses for Taupō and Waimihia;
Mamaku and Rotoma-D; and Waiohau, Rotorua, and Rerewhakaaitu (Table 4).
Results of Euclidean similarity coefficient (ESC) calculations for
major-element (a) and trace-element (b) concentrations in glass
from all the tephras analysed. See Supplement Material 2 for R code used
for these calculations. Colour coding shows ESC values: white shows the
smaller the value (similar compositions) through to black showing the larger
the values (different compositions). The lowest values (< 0.2) and
hence the most similar tephras compositionally (based on Al2O3,
K2O, SiO2, Na2O, TiO2, FeOtt, and MnO major elements and
V, Co, Rb, Nd, Eu, Yb, Th, and U trace elements) are highlighted with bold
outlines and red text. Tephras from Taupō Volcanic Centre are shaded
red, and those from Okataina Volcanic Centre are shaded blue.
Geochemically similar tephra and the identified distinctions from
this research.
a Ages from Table 1 and references therein.
b Volumes from Lowe et al. (2008) and references therein, except for Tahuna,
Rotoiti/Rotoehu, and Unit L (Mangaone Subgroup).c Tahuna tephra-fall
volume estimate in km3 from Froggatt and Lowe (1990). d Rotoehu
tephra-fall volume in km3 from Froggatt and Lowe (1990). e Unit L
tephra-fall volume in km3 from Jurado-Chichay and Walker (2000).
Table 5 outlines the key eruptions that show similar geochemical signatures
in their glass chemistry and the ways in which they can be distinguished.
Figure 14a shows that for Poihipi and Tahuna the best separation
(although some overlap remains) is seen in the ratios La/Yb vs. Ba/Y; in
addition, Tahuna also shows a bimodality in Ba/Th ratio which is not seen
for Poihipi. For Rotoma and Mamaku, the tephras can be separated (although
some overlap remains) using Ba/Th vs. Rb/Sr and Rb/Zr vs. Rb/Sr
(Fig. 14b). Rotoma and Rotoehu/Rotoiti are very similar in their
glass-shard major elements though they can be distinguished using specific, but a
wide range of, trace elements (Fig. 14c). They are also very
different in age and hence should not be too difficult to distinguish on the
basis of stratigraphic positioning or dating.
Waimihia and Unit K (Taupō Subgroup) tephras are very difficult to
distinguish, and their similar Late- to Mid-Holocene ages (3382 ± 50
and 5088 ± 73 cal yr BP, respectively; Lowe et al., 2013) and
mineralogy could see them misidentified if dates were unavailable or
imprecise. Geochemical investigation beyond the PCA and SC analyses of glass
shows that Lu, Sc, Mn, and Co can be used to geochemically distinguish these
two tephras (Fig. 14d), indicative of fractional crystallisation of
differing amounts of clinopyroxene, plagioclase, and amphibole during the
eruptive events. Although not identified by the SC analysis directly,
Poronui (11 195 ± 51 cal yr BP) and Karapiti (11 501 ± 104 cal yr BP) tephras also have comparable age, geochemistry, and mineralogy; thus
using major element, trace element, and trace-element ratios these two tephras remain
indistinguishable. Glass shards from the three Holocene tephras, Waimihia,
Poronui, and Karapiti, also have very similar trace element and
trace-element ratios, but, as for Waimihia and Unit K, they can be
distinguished with Lu, Sc, Mn, and Co, where Waimihia has higher Sc, Lu, and
Mn but lower Co in comparison to those of the Poronui and Karapiti tephras.
They can also be distinguished simply with a biplot of FeOt vs. CaO, or
Na2O+K2O or SiO2/K2O, or SiO2, where the Waimihia
samples in general have lower FeOt, Na2O+K2O, and SiO2/K2O
and higher CaO and SiO2 in comparison to the equivalent values for
Poronui and Karapiti samples (Fig. 14e, Table 4).
Geochemical investigation and PCA also highlight the similarity of the
glasses of Waiohau, Rotorua, and Rerewhakaaitu tephras. There is added
complexity with these samples as we have both proximal and distal deposits
to compare, where, as discussed previously, the proximal samples will likely
be more heterogeneous. Glass analyses of the Waiohau tephra show it can be
distinguished from those for the Rotorua and Rerewhakaaitu tephras using a
range of trace elements and trace-element ratios. In addition, the Rotorua
and Rerewhakaaitu tephras are observed to be bimodal for some elements. The
Waiohau tephra also has different mineralogy from that of Rotorua and Rerewhakaaitu
tephras (Froggatt and Lowe, 1990; Lowe et al., 2008). Conversely, the
Rotorua and Rerewhakaaitu tephras are indistinguishable in geochemistry and
mineralogy, and therefore accurate dating and stratigraphic
super-positioning would have to be relied upon to distinguish them with
certainty (Fig. 14f, Table 4).
Biplots to show examples of how trace elements in glass enable
manipulation of heterogeneous and bimodal geochemical data. Panel (a) shows
analyses of glass from Kaharoa and Taupō tephras, both of which show a
heterogeneous signature with most major elements (presented on a normalised
basis). Sr has a low variability for Taupō but does not for Kaharoa
tephra; conversely, Ba has a low variability for Kaharoa but does not for
Taupō. Panel (b) shows the bimodal signature created for Tahuna tephra
using K2O composition; this is also seen for Cs but not for Ba.
Biplots for glass analyses for specific tephras which have very
similar compositions and similar ages (see text for discussion and Table 5
for alternative elements). Plots show examples of the elements in glass that
enable these tephras to be separated: (a) Poihipi and Tahuna (from TVC); (b) Mamaku and Rotoma-D (from OVC; note no trace-element data were obtained for
Rotoma-P); (c) Rotoma and Rotoiti/Rotoehu (from OVC); (d) Waimihia and Unit
K (from TVC); (e) Waimihia, Poronui and Karapiti – note that Poronui and
Karapiti are indistinguishable using glass chemistry; and (f) Waiohau,
Rerewhakaaitu and Rotorua – note that Rerewhakaaitu and Rotorua are
indistinguishable using glass chemistry. All major-element data are
presented on a normalised basis, and total iron is expressed as FeO.
KOT, Okaia, and Unit L (Mangaone Subgroup) show indistinguishable major
elements in their constituent glass shards and very similar trace elements.
The TephraNZ samples have been compared with existing published data and are
complementary with the existing data with respect to major elements (e.g.
Sandiford et al., 2002; Shane et al., 2002; Smith et al., 2002, 2005; Lowe
et al., 2008; Allan et al., 2008; Molloy, 2008). This is the first time
trace-element glass data have been published for Unit L and Okaia tephras.
Our results show that Unit L glass shows bimodality in Rb/Zr, Ba/Th, Ce/Th,
and Y/Th, and in this way, it can therefore be distinguished from the KOT and
Okaia tephras (Table 5).
Proposed future research
This foundation dataset, derived in a formalised way, is unique in New
Zealand and provides researchers with new avenues of research. It is our aim
that the foundation dataset can be improved and expanded with analyses of
other known deposits and that a subsidiary catalogue of accurately
correlated geochemical analyses for such deposits can be added to bolster
the dataset. As noted earlier, it is beyond the scope of this paper to dive
too deeply into the detail of the data, but we feel that it will provide the
basis for countless projects in the future. Below we highlight some of the
current gaps which we think would benefit from further research.
Further statistical analysis
We have applied simple ordination and statistical analyses to this dataset;
however, we believe that further rigorous statistical analysis could be
applied. Firstly, the analyses we present in this publication have been
applied to mean values for each of the tephra samples (e.g. data from
Table 2); there is no reason why these simple tests could not be
applied to the full dataset, using all the individual (shard by shard)
values analysed for each sample. Secondly, we chose very basic tests (PCA
and ESC) to fit with our requirements, but there is likely some more
appropriate statistical test that could be applied to get the most out of
this exceptional dataset. For example, (extended) canonical variate
analysis (CVA): applying CVA to PCA results could determine optimal
discrimination between multivariate data for single tephra deposits. This
discrimination will increase the ability to identify an unknown tephra based
on its similarity to known signatures plotted in multivariate space (e.g.
discriminant function analysis; Tyron et al., 2009, 2010; Lowe et al., 2017;
Bolton et al., 2020).
Whanganui Basin correlatives
A number of the tephras reported in this research were sampled from the
Whanganui Basin, an uplifted Plio-Pleistocene basin margin sequence that
preserves as many as 45 superposed cyclothems deposited since
∼ 3 Ma (Naish et al., 1996, 2005; Naish and Kamp, 1997; Carter
and Naish, 1998; Carter et al., 1999; Pillans, 2017; Grant et al., 2018,
2019; Tapia et al., 2019). The tephra deposits within the basin contribute
to the robust chronological framework that has been constructed for this
region (Seward, 1976; Beu and Edwards, 1984; Alloway et al., 1993; Naish and
Kamp, 1995; Shane et al., 1996; Saul et al., 1999; Pillans et al., 1994,
2005; Naish et al., 1996, 2005; Rees et al., 2018, 2019, 2020; Hopkins et
al., 2021). These and other tephras (such as those derived from Tauranga
Volcanic Centre) also record a critical time in New Zealand's volcanological
history – the transfer between activity from the Coromandel Volcanic Zone
to the Taupō Volcanic Zone (Briggs et al., 2005; Pittari et al., 2021).
Deposits from this period are generally poorly exposed at source, and thus
distal tephras could provide an insight into the eruptive history,
geochemical evolution, and potentially even caldera evolution during this
period (Houghton et al., 1995; Pittari et al., 2021). Most of the tephras
reported in this research are well known and well dated, which is why they
were included in the study. However, most do not have a known source caldera
or source eruptives, or they have only been variably correlated to other deposits
in New Zealand (e.g. Lowe et al., 2001; Pearce et al., 2008). There are also
a number of tephra deposits in the Whanganui Basin that have yet to be
studied, and thus a research project that is tephra focused, rather than
using it as an accessory to a different line of enquiry, is timely.
IODP and ODP correlatives
At present there is a wealth of information that has yet to be fully
investigated in the tephra record of the ODP Leg 181 Sites 1122, 1123, 1124, and
1125 (Carter et al., 2003, 2004; Alloway et al., 2005; Allan et al., 2008)
and IODP Expedition 372 and 375 sites U1517 and U1520 (Pecher et al., 2018;
Saffer et al., 2018). Pioneering work includes that undertaken by Watkins
and Huang (1977) and Nelson et al. (1985), and findings from more “local”
marine coring expeditions include those reported by Shane et al. (2006). The
new reference material built by this project will allow more definitive
identification and correlation of tephras within these cores, specifically
post-2 Ma. However, the reports currently published on these deposits
suggest that there are many more tephra deposits to be found in these marine
and offshore sites than we have in the TephraNZ dataset (Carter et al.,
2003; Alloway et al., 2005; Holt et al., 2010, 2011; Hopkins et al., 2021).
The TephraNZ dataset can provide a formalised correlation framework from
which other unknown deposits can be determined, characterised, and
integrated into a holistic tephrostratigraphic reconstruction. Allan (2008)
and Allan et al. (2008) reported the major- and trace-element geochemistry of
glass shards for tephra deposits dating from ∼ 1.65 Ma in the
ODP 1123 core. They also give orbitally tuned ages for these tephras.
However, of the 38 identified tephras only 7 were correlated to onshore
equivalents. In addition, Alloway et al. (2005) reported over 100 tephra
layers in the four ODP Leg 181 cores, dating back through orbital tuning
(astrochronology) to 1.81 Ma. Using major-element chemistry of constituent
glass shards, 13 tephras were correlated to equivalent onshore tephras
including KOT, Omataroa, Rangitawa/Onepuhi, Kaukatea, Kidnappers-B and
Kidnappers-A/Potaka, Unit D/Ahuroa, Ongatiti, Rewa, Sub-Rewa, Pakihikura, Ototoka, and
Table Flat. Analyses of glass from some of these are currently not in the
TephraNZ database but could be easily added if the appropriate reference
samples were available along with the capacity to analyse them. Alloway et
al. (2005) reported an additional six tephra deposits that are correlated
between the cores, but not to onshore equivalents, leaving potentially
∼ 81 tephra horizons within the ODP cores that are
uncorrelated. The information that could be derived from their analysis would
provide many details about the timing and evolution of the TVZ eruptions
that are currently unobtainable from onshore deposits.
Dominant ferromagnesian. Mineral assemblages for late Quaternary
silicic tephra deposits updated from Froggatt and Lowe (1990). Plag –
plagioclase feldspar; opx – orthopyroxene; mnt – magnetite; ilm –
ilmenite; hyp – hypersthene; hbl – hornblende; bio – biotite; cgt –
cummingtonite; aug – augite. The mineral assemblages are listed with
mineral species in order of abundance; the diagnostic mineral in each
assemblage is in bold. Tephras are listed multiple times if their mineral
assemblage changes through the eruption sequence, and deposits in brackets
are not included in the TephraNZ database.
Assemblage 1aAssemblage 2Assemblage 3Assemblage 4Assemblage 5Assemblage 6Plag ± opx ± mnt ± ilmHyp + hbl ± augHyp + hbl + bioHyp + cgt ± hblHyp + aug ± hblAegirinebTaupō VCOkataina VCOkataina VCOkataina VCOkataina VCTuhua VC (Mayor Is)Taupō – Unit YMamakuKaharoaWhakatāneHauparuTuhua(Mapara – Unit X)WaiohauRotorua (upper)RotomaTe Mahoe(Whakaipo – Unit V)Rotorua (lower)RerewhakaaituRotoiti/Rotoehu (all)MaketūWaimihia – Unit SUnit LŌkārekaUnit KTe RereRotoiti/Rotoehu (upper)(Motuterec – Units G & H)(Omataroa)Ōpepe – Unit EAwakeriKapenga VCPoronui – Unit CMangaoneEarthquake FlatKarapiti – Unit BTahunaNgāmotuMaroa VCPuketarataTaupō VCKawakawa (all)PoihipiOkaia(Tihoi)(Waihora)(Otake)
a Assemblage 1 updated
using Barker et al. (2015). b Assembly 6 aegirine ± riebeckite ± aenigmatite ± olivine ± tuhualite. c Motutere
was listed in Froggatt and Lowe (1990) as a single unit with Assemblage 1
mineralogy, but this has subsequently been redefined by Wilson (1993) into two
subunits G and H, which do not have their independent assemblages defined.
Mineral compositions
The TephraNZ reference dataset is only populated by glass major- and trace-element analyses at present. This is because glass geochemistry is one of
the most frequently used and accessible tools for tephra correlation.
Aerodynamic sorting of tephra componentry through transportation adds to the
favourability of glass shards as the dominant tool because glass shards tend
to be the only phase that is found at both proximal and distal sites.
However, previous New Zealand-based studies have specified how mineral
assemblages and their geochemical compositions can be used to distinguish
certain tephras and their source (e.g. Nairn and Kohn, 1973; Lowe, 1988;
Froggatt and Lowe, 1990; Froggatt and Rogers, 1990; Shane, 1998; Shane et
al., 2003b; Allan et al., 2008; Lowe et al., 2008; Lowe, 2011). For example,
the mineral cummingtonite, where predominant, is a known identifier for
tephras from the Haroharo complex of the OVC (Whakatāne, Rotoma,
Rotoehu/Rotoiti (Table 5); Ewart, 1968; Lowe, 1988; Froggatt and
Lowe, 1990). At present, ferromagnesian mineralogical assemblages (following
Froggatt and Lowe, 1990; Smith et al., 2005; Lowe et al., 2008) for all the
TephraNZ samples younger than and including Rotoehu/Rotoiti have been
published (see Table 5). Extending this tabulation to include the
older samples would add another useful criterion to the correlation toolbox
for tephras containing ferromagnesian minerals.
Additionally, the fractional crystallisation of plagioclase, biotite,
amphibole, zircon, hydrous mineral phases, or Fe–Ti oxides has been shown to
be the key impactor on the trace-element chemistry (Shane, 1998; Allan,
2008; Turner et al., 2009, 2011). Thus the prevalence of these minerals is
also an important potential fingerprinting tool. The information on the
mineralogy of the tephras is not only useful for fingerprinting but also can
be used in determining the characteristics of the magma source components
and potentially provide estimates for the temperature, pressure, and
oxidation states of the magmatic system before eruption (e.g. Lowe, 1988,
2011; Shane, 1998). Thus, this information can allow hypotheses to be
developed on the reactivation and triggering of these large-scale eruptions,
an important step for hazard and risk monitoring.
The New Zealand tephra “Bermuda Triangle”
At present the TephraNZ database is very well populated for samples from the
Rotoiti/Rotoehu through to Kaharoa eruption. It also has a high number of
samples, but not an exhaustive list, from Mamaku ignimbrite (∼ 0.22–0.23 ka) to the Hikuroa Pumice (2 Ma). There is a stark deficit in
tephras between the Rotoiti/Rotoehu eruption and Mamaku ignimbrite
(Table 1). This ∼ 150 kyr gap in the volcanic record
(∼ 220 to 45 ka) is intriguing as there is proximal
evidence for activity during this period. For example, Rosenberg et al. (2020) reported the occurrence of volcanic formations in cores forms the
Taupō region in the age range of ∼ 168 to 92 ka, including
the Huka Falls formations, Racetrack rhyolites, and the Te Mihi rhyolites.
Tephra deposits, in some cases strongly weathered successions of multiple
units broadly lumped together as a “formation”, such as the so-called
Hamilton Ash Formation, have been reported during this time period both
terrestrially and in marine and lacustrine sediment cores (Ward, 1967; Pain,
1975; Vucetich et al., 1978; Iso et al., 1982; Froggatt, 1983; Manning,
1996; Lowe et al., 2001; Newnham et al., 2004; Allan et al., 2008; Briggs et
al., 2006; Lowe, 2019; Benjamin Laeuchli, personal communication, 2020). However, at present the authors
are not aware of a detailed, up-to-date study into the primary compositions
of these tephra deposits. The key deposits identified during this time
period include (but are not limited to) Kaingaroa Ignimbrite
(∼ 0.18 Ma; Froggatt, 1983), Tablelands Tephra Formation
(∼ 0.21–0.18 Ma; Iso et al., 1982, 0.39–0.34 Ma; Manning,
1996), Hamilton Ash Formation (0.34–0.125 Ma; Lowe, 2019), Kutarere tephra
(= Mamaku ignimbrite 0.22–0.23 Ma; Shane et al., 1994; Houghton et al.,
1995; Black et al., 1996; Tanaka et al., 1996; Milner et al., 2003), Kukumoa
Subgroup (∼ 0.22–0.05 Ma; Manning, 1996), and Tikotiko Ash
(∼ 0.125 ka; Lowe, 2019). A number of these studies are
outdated, and with improved methodologies (major- and trace-element analysis,
potentially of melt inclusions where preserved, dating techniques, and other
measures to help construct time frames such as via phytolith studies to
determine glacial vs. interglacial periods, and potentially also
paleomagnetic measures as shown for the much older and very strongly
weathered Kauroa Ash Formation: Hopkins et al., 2021) it could be timely to
further investigate this period of (apparent) deficit.
Conclusions
Major- and trace-element geochemical compositions of glass shards for a large
suite of prominent, widespread New Zealand rhyolitic tephras have been
analysed systematically and published for the first time as TephraNZ.
TephraNZ is a foundation dataset for collating geochemical data about New
Zealand tephras based on analyses of their glass components. The foundation
reference dataset is made up of known deposits that have their ages
quantified through independent methods, and/or are from the type sites where
tephras were first defined, or well-documented reference sections. Detailed
methodology is reported to allow subsequent research to acquire comparable
data to those in this database. Principal component analysis of the glass
geochemistry indicates that for the TephraNZ foundation dataset, as a whole,
major elements Al, K, Si, Ti, Fe, Mn, and Cl are responsible for the spread
along PC1 and PC2 space. When the trace elements are run together with the
major elements, V, Co, Mg, Cu, Ti, Sr, Sc, Ca, Cs, Zr, Th, and Rb are most
responsible for the separation in PC1 and PC2 space. Euclidean similarity
coefficients can also be used to distinguish between some geochemically
similar glass analyses. However, further detailed geochemical investigation
is required to distinguish others. Geochemically indistinguishable tephras
(on the basis of both major- and trace-element glass-shard compositions) are
identified as Taupō and Waimihia; Poronui and Karapiti; Rotorua and
Rerewhakaaitu; and KOT and Okaia. Only Poronui and Karapiti are noted as
entirely indistinguishable, with other methods of characterisation listed as
alternative options, including mineralogy, age, and stratigraphic
relationships.
Data availability
All the data provided in this article are available as Excel files in the Supplement. The data are also available from GNS Science, New Zealand, at Pet Lab
(https://pet.gns.cri.nz, GNS Science, 2004), and as a file submission on EarthChem (10.26022/IEDA/111724, Hopkins et al., 2020b).
The supplement related to this article is available online at: https://doi.org/10.5194/gchron-3-465-2021-supplement.
Author contributions
JLH and RJW designed the project. DJL and BJP contributed samples from
previous field campaigns, and DJL provided guidance on new and existing
field locations for sample collection. JLH and JEB undertook the fieldwork,
lab work, analysis, and data reduction. ABHR advised on statistical analysis
and R coding. LA supervised and helped JEB develop LA-ICP-MS analysis and
data reduction. FT supervised and helped JEB develop sample mounting and
polishing procedures. JLH wrote the manuscript with contributions from all
co-authors.
Competing interests
The authors declare that they have no conflict of interest.
Disclaimer
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Acknowledgements
This research was funded partly through the Victoria University of
Wellington (VUW) Summer Scholarship programme, of which Janine E. Bidmead was the recipient
(project code 136, 2019–2020), with a matched contribution from Jenni L. Hopkins's
Marsden Fast-Start. Jenni L. Hopkins and Richard J. Wysoczanski are also funded through Jenni L. Hopkins's Marsden Fast-Start project (Te Pūtea Rangahau a Marsden) from the Royal Society of
New Zealand (Royal Society Te Apārangi) contract MFP-VUW1809. Some of
the fieldwork for tephra collection, sample analysis, and data reduction
was supported by David J. Lowe's (2011–2014) Marsden Fund (Te Pūtea Rangahau a
Marsden) from the Royal Society of New Zealand (Royal Society Te
Apārangi) contract UOW1006, and the DEVORA project. The paper is an
output of the Commission on Tephrochronology (COT) of the International
Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI).
The authors would like to thank James Crampton (VUW), Grace Frontin-Rollet
(NIWA), Michael Gazley (RSC Mining and Mineral Exploration), and Shaun Eaves
(VUW) for statistical discussion and advice. We would also like to thank
Britta Jensen, Maxim Portnyagin, Stephen Kuehn, and an anonymous reviewer for
their detailed and helpful comments and reviews in the development of this
article and the dataset.
Financial support
This research has been supported by the Royal Society of New Zealand (Royal Society Te Apārangi) (grant nos. MFP-VUW1809 and UOW1006) and the Victoria University of Wellington Summer Scholarship programme (grant no. 136 (2019–2020)).
Review statement
This paper was edited by Britta Jensen and reviewed by Maxim Portnyagin, Stephen Kuehn, and one anonymous referee.
ReferencesAbbott, P., Bonadonna, C., Bursik, M., Cashman, K., Davies, S., Jensen, B.,
Kuehn, S., Kurbatov, A., Lane, C., Plunkett, G., Smith, V., Thomlinson, E.,
Thordarsson, T., Walker, D. J., and Wallace, K.: Community Established Best
Practice Recommendations for Tephra Studies-from Collection through Analysis
(Version 3.0.0), Zenodo [data set],
10.5281/zenodo.5047775, 2021.Allan, A. S.: An elemental and isotopic investigation of Quaternary silicic
Taupo Volcanic Zone tephras from ODP Site 1123: chronostratigraphic and
petrogenetic applications, MSc thesis, Victoria University of Wellington,
Wellington, New Zealand, 2008.Allan, A. S., Baker, J. A., Carter, L., and Wysoczanksi, R. J.: Reconstructing
the Quaternary evolution of the world's most active silicic volcanic system:
insights from an ∼ 1.65 Ma deep ocean tephra record sourced from Taupo
Volcanic Zone, New Zealand, Quaternary Sci. Rev., 27, 2341–2360,
2008.Allan, A. S. R., Wilson, C. J. N., Millet, M.-A., and Wysoczanski, R. J.: The
invisible hand: tectonic triggering and modulation of a rhyolitic
supereruption, Geology, 40, 563–566, 2012.Alloway, B. V., Pillans, B. J., Sandhu, A. S., and Westgate, J. A.: Revision of
the marine chronology in the Wanganui Basin, New Zealand, based on the
isothermal plateau fission-track dating of tephra horizons, Sediment.
Geol., 82, 299–310, 1993.Alloway, B. V., Pillans, B. J., Carter, L., Naish, T. R., and Westgate, J. A.:
Onshore–offshore correlation of Pleistocene rhyolitic eruptions from New
Zealand: implications for TVZ eruptive history and paleoenvironmental
construction, Quaternary Sci. Rev., 24, 1601–1622, 2005.Alloway, B. V., Lowe, D. J., Larsen, G., Shane, P. A. R., and Westgate, J. A.:
Tephrochronology, in: The Encyclopaedia of
Quaternary Science, edited by: Elias, S. A. and Mock, C. J., 2nd Edn., 4, Elsevier, London, 277–304, 2013.Barker, S. J., Wilson, C. J., Allan, A. S., and Schipper, C. I.: Fine-scale
temporal recovery, reconstruction and evolution of a post-supereruption
magmatic system, Contrib. Mineral. Petr., 170, 1–40, 2015.Barker, S. J., Wilson, C. J. N., Morgans, D. J., and Rowland, J. V.: Rapid priming,
accumulation, and recharge of magma driving recent eruptions at a
hyperactive caldera volcano, Geology, 44, 323–326, 2016.Barker, S. J., Van Eaton, A. R., Mastin, L. G., Wilson, C. J. N., Thompson, M. A.,
Wilson, T. M., Davis, C., and Renwick, J. A.: Modeling ash dispersal from future
eruptions of Taupo supervolcano, Geochem. Geophy. Geosy., 20, 3375–3401, 2019.Barker, S. J., Wilson, C. J. N., Illsley-Kemp, F., Leonard, G. S., Mestel,
E. R. H., Mauriohooho, K., and Charlier, B. L. A.: Taupō: an overview of New
Zealand's supervolcano, New Zeal. J. Geol. Geop., 64, 320–346,
10.1080/00288306.2020.1792515, 2021.Barrell, D. J. A., Almond, P. C., Vandergoes, M. J., Lowe, D. J., Newnham, R. M.,
and NZ-INTIMATE members: A composite pollen-based stratotype for
inter-regional evaluation of climatic events in New Zealand over the past
30,000 years (NZ-INTIMATE project), Quaternary Sci. Rev., 74, 4–20, 2013.Beu, A. G. and Edwards, A. R.: New Zealand Pleistocene and late Pliocene
glacio-eustatic cycles, Palaeogeogr. Palaeoclim., 46, 119–142, 1984.Black, T. M., Shane, P. A., Westgate, J. A., and Froggatt, P. C.: Chronological
and palaeomagnetic constraints on widespread welded ignimbrites of the Taupo
volcanic zone, New Zealand, Bull. Volc., 58, 226–238, 1996.Bland, K. J., Kamp, P. J., and Nelson, C. S.: Systematic lithostratigraphy of the
Neogene succession exposed in central parts of Hawke's Bay Basin, eastern
North Island, New Zealand. Ministry of Economic Development New Zealand
Unpublished Petroleum Report PR3724, 259 pp., 2007.Bolton, M. S., Jensen, B. J., Wallace, K., Praet, N., Fortin, D., Kaufman, D.,
and De Batist, M.: Machine learning classifiers for attributing tephra to
source volcanoes: an evaluation of methods for Alaska tephras, J. Quaternary
Sci., 35, 81–92, 2020.Briggs, R. M., Houghton, B. F., McWilliams, M., and Wilson, C. J. N.:
40Ar/39Ar ages of silicic volcanic rocks in the TaurangaKaimai
area, New Zealand: dating the transition between volcanism in the Coromandel
Arc and the Taupo Volcanic Zone, New Zeal. J. Geol. Geop., 48, 459–469, 2005.Briggs, R. M., Lowe, D. J., Esler, W. R., Smith, R. T., Henry, M. A. C., Wehrmann,
H., and Manning, D. A.: Geology of the Maketu area, Bay of Plenty, North
Island, New Zealand. Sheet V14 1:50000, Department of Earth and Ocean
Sciences, University of Waikato, Occasional Report 26, 43 pp. + Map, 2006.Buck, M. D., Briggs, R. M., and Nelson, C. S.: Pyroclastic deposits and volcanic
history of Mayor Island, New Zeal. J. Geol. Geop., 24, 449–467, 1981.Bussell, M. R.: Palynological evidence for upper Putikian (middle Pleistocene)
interglacial and glacial climates at Rangitawa Stream, south Wanganui Basin,
New Zealand, New Zeal. J. Geol. Geop., 29, 471–479, 1986.Bussell, M. R. and Pillans, B.: Vegetational and climatic history during
oxygen isotope stage 7 and early stage 6, Taranaki, New Zealand, J. Royal
Soc. New Zeal., 27, 419–438, 1997.Carter, L., Nelson, C. S., Neil, H. L., and Froggatt, P. C.: Correlation,
dispersal, and preservation of the Kawakawa Tephra and other late Quaternary
tephra layers in the Southwest Pacific Ocean, New Zeal. J. Geol.
Geop., 38, 29-46, 1995.Carter, L., Shane, P., Alloway, B., Hall, I. R., Harris, S. E., and Westgate,
J. A.: Demise of one volcanic zone and birth of another – a 12 my marine
record of major rhyolitic eruptions from New Zealand, Geology, 31, 493–496, 2003.Carter, L., Alloway, B., Shane, P., and Westgate, J.: Deep-ocean record of
major late Cenozoic rhyolitic eruptions from New Zealand, New Zeal. J. Geol.
Geop., 47, 481–500, 2004.Carter, R. M. and Naish, T. R.: A review of Wanganui Basin, New Zealand: global
reference section for shallow marine, Plio–Pleistocene (2.5–0 Ma)
cyclostratigraphy, Sediment. Geol., 122, 37–52, 1998.Carter, R. M., Abbott, S. T., and Naish, T. R.: Plio-Pleistocene cyclothems from
Wanganui Basin, New Zealand: type locality for an astrochronologic
time-scale, or template for recognizing ancient
glacio-eustacy?, P. Roy. Soc. Lond. A, 357, 1861–1872, 1999.Charlier, B. L. A. and Wilson, C. J. N.: Chronology and evolution of
caldera-forming and post caldera magma systems at Okataina Volcano, New Zealand from zircon U–Th
model-age spectra, J. Petrol., 51, 1121–1141, 2010.Cole, J. W., Deering, C. D., Nairn, B. R. M., Sewell, S., Shane, P. A. R. and Matthews, N. E.: Okataina Volcanic Centre, Taupo Volcanic Zone, New Zealand: A review of
volcanism and synchronous pluton development in an active, dominantly silicic caldera
system, Earth Sci. Rev., 128, 1–17, 2014.Cooper, G. F., Wilson, C. J. N., Millet, M.-A., Baker, J. A., and Smith, E. G. C.:
Systematic tapping of independent magma chambers during the 1 Ma Kidnappers
supereruption, Earth Planet Sc. Lett., 313, 23–33, 2012.Curran, J.: Hotelling: Hotelling's T'2 Test and Variants, R
package version 1.0-5, available at: https://CRAN.R-project.org/package=Hotelling (last access: June 2021), 2018.Danišík, M., Shane, P., Schmitt, A. K., Hogg, A., Santos, G. M.,
Storm, S., Evans, N. J., Fifield, L. K., and Lindsay, J. M.: Re-anchoring the
late Pleistocene tephrochronology of New Zealand based on concordant
radiocarbon ages and combined 238U/230Th disequilibrium and
(U–Th)/He zircon ages, Earth Planet Sc. Lett., 349, 240–250, 2012.Danišík, M., Lowe, D. J., Schmitt, A. K., Friedrichs, B., Hogg, A. G., and Evans, N. J.: Sub-millennial eruptive recurrence in the
silicic Mangaone Subgroup tephra sequence, New Zealand, from Bayesian
modelling of zircon double-dating and radiocarbon ages, Quaternary Sci.
Rev., 246, 106517, 10.1016/j.quascirev.2020.106517, 2020.Denton, J. S. and Pearce, N. J.: Comment on “A synchronized dating of three
Greenland ice cores throughout the Holocene” by BM Vinther et al.: No
Minoan tephra in the 1642 BC layer of the GRIP ice core, J. Geophys.
Res., 113, D04303, 10.1029/2007JD008970, 2008.Dugmore, A. J., Larsen, G., and Newton, A. J.: Tephrochronology and its
application to late Quaternary environmental reconstruction, with special
reference to the North Atlantic islands, in:
Tools for Constructing Chronologies: Cross Disciplinary Boundaries, edited by: Buck, C. E. and Millard A. R., Lecture
Notes in Statistics, Springer, London, 177, 173–188, 2004.Erdman, C. F. and Kelsey, H. M.: Pliocene and Pleistocene stratigraphy and
tectonics, Ohara Depression and Wakarara Ra-nge, North Island, New
Zealand, New Zeal. J. Geol. Geop., 35, 177–192, 1992.Ewart, A.: The Petrography of the Central North Island Rhyolitic Lavas: Part
2 – Regional Petrography Including Notes on Associated Ash-Flow Pumice
Deposits, New Zeal. J. Geol. Geop., 11, 478–545, 1968.Flude, S. and Storey, M.: 40Ar/39Ar age of the Rotoiti Breccia and Rotoehu
Ash, Okataina Volcanic Complex, New Zealand, and identification of
heterogeneously distributed excess 40Ar in supercooled crystals, Quat.
Geochronol., 33, 13–23, 2016.Froggatt, P. C.: Toward a comprehensive Upper Quaternary tephra and ignimbrite
stratigraphy in New Zealand using electron microprobe analysis of glass
shards, Quaternary Res., 19, 188–200, 1983.Froggatt, P. C.: Standardization of the chemical analysis of tephra deposits,
Report of the ICCT working group, Quatern. Int., 13–14, 93–96, 1992.Froggatt, P. C. and Lowe, D. J.: A review of late Quaternary silicic and some
other tephra formations from New Zealand: their stratigraphy, nomenclature,
distribution, volume, and age, New Zeal. J. Geol. Geop., 33, 89–109,
1990.Froggatt, P. C. and Rogers, G. M.: Tephrostratigraphy of high-altitude peat
bogs along the axial ranges, North Island, New Zealand, New Zeal. J. Geol.
Geop., 33, 111–124, 1990.Gehrels, M. J., Lowe, D. J., Hazell, Z. J., and Newnham, R. M.: A continuous
5300-yr Holocene cryptotephrostratigraphic record from northern New Zealand
and implications for tephrochronology and volcanic hazard assessment,
Holocene, 16, 173–187, 2006.GNS Science: Petlab: New Zealand's national rock, mineral and geoanalytical database, GNS Science [data set], 10.21420/9DJH-RP34, 2004.Grant, G. R., Sefton, J. P., Patterson, M. O., Naish, T. R., Dunbar, G. B.,
Hayward, B. W., Morgans, H. E. G., Alloway, B. V., Seward, D., Tapia, C. A., and
Prebble, J. G.: Mid-to late Pliocene (3.3–2.6 Ma) global sea-level
fluctuations recorded on a continental shelf transect, Whanganui Basin, New
Zealand, Quaternary Sci. Rev., 201, 241–260, 2018.Grant, G. R., Naish, T. R., Dunbar, G. B., Stocchi, P., Kominz, M. A., Kamp,
P. J., Tapia, C. A., McKay, R. M., Levy, R. H., and Patterson, M. O.: The
amplitude and origin of sea-level variability during the Pliocene
epoch, Nature, 574, 237–241, 2019.Gravely, D. M., Wilson, C. J. N., Rosenberg, M. D., and Leonard, G. S.: The nature
and age of Ohakuri Formation and Ohakuri Group rocks in surface exposures
and geothermal drillhole sequences in the central Taupo Volcanic Zone, New
Zealand, New Zeal. J. Geol. Geop., 49, 305–308, 2006.Gravely, D. M., Wilson, C. J. N., Leonard, G. S., and Cole, J. W.: Double trouble:
Paired ignimbrite eruptions and collateral subsidence in the Taupo Volcanic
Zone, New Zealand, Geol. Soc. Am. Bull., 119, 18–30, 2007.Hogg, A. G. and McCraw, J. D.: Late Quaternary tephras of Coromandel Peninsula,
North Island, New Zealand: a mixed peralkaline and calcalkaline tephra
sequence, New Zeal. J. Geol. Geop., 26, 163–187, 1983.Hogg, A. G., Higham, T. F. G., Lowe, D. J., Palmer, J., Reimer, P., and Newnham,
R. M.: A wiggle-match date for Polynesian settlement of New Zealand,
Antiquity, 77, 116–125, 2003.Hogg, A. G., Lowe, D. J., Palmer, J. G., Boswijk, G., and Bronk Ramsey, C. J.:
Revised calendar date for the Taupo eruption derived by 14C
wiggle-matching using a New Zealand kauri 14C calibration data set,
Holocene, 22, 439–449, 2012.Hogg, A. G., Wilson, C. J. N., Lowe, D. J., Turney, C. S. M., White, P., Lorrey,
A. M., Manning, S. W., Palmer, J. G., Bury, S., Brown, J., Southon, J., and
Petchey, F.: Wiggle-match radiocarbon dating of the Taupo eruption, Nature
Comm., 10, 4669, 10.1038/s41467-019-12532-8, 2019.Holt, K., Wallace, R. C., Neall, V. E., Kohn, B. P., and Lowe, D. J.: Quaternary
tephra marker beds and their potential for palaeoenvironmental
reconstruction on Chatham Islands east of New Zealand, southwest Pacific
Ocean, J. Quaternary Sci., 25, 1169–1178, 2010.Holt, K. A., Lowe, D. J., Hogg, A. G., and Wallace, R. C.: Distal occurrence of
mid-Holocene Whakatane Tephra on the Chatham Islands, New Zealand, and
potential for cryptotephra studies, Quatern. Int., 246, 344–351, 2011.Hopkins, J. L. and Seward, D.: Towards robust tephra correlations in early and
pre-Quaternary sediments: A case study from North Island, New Zealand, Quat.
Geochronol., 50, 91–108, 2019.Hopkins, J. L., Millet, M. A., Timm, C., Wilson, C. J., Leonard, G. S., Palin,
J. M., and Neil, H.: Tools and techniques for developing tephra stratigraphies
in lake cores: a case study from the basaltic Auckland Volcanic Field, New
Zealand, Quaternary Sci. Rev., 123, 58–75, 2015.Hopkins, J. L., Wilson, C. J., Millet, M. A., Leonard, G. S., Timm, C., McGee,
L. E., Smith, I. E., and Smith, E. G.: Multi-criteria correlation of tephra
deposits to source centres applied in the Auckland Volcanic Field, New
Zeal. Bull. Volc., 79, 55, 10.1007/s00445-017-1131-y, 2017.Hopkins, J. L., Wysoczanski, R. J., Orpin, A. R., Howarth, J. D., Strachan,
L. J., Lunenburg, R., McKeown, M., Ganguly, A., Twort, E., and Camp, S.:
Deposition and preservation of tephra in marine sediments at the active
Hikurangi subduction margin, Quaternary Sci. Rev., 274, 106500,
10.1016/j.quascirev.2020.106500, 2020a.Hopkins, J. L., Bidmead, J. E., Lowe, D. J., Wysoczanski, R. J., Pillans, B. J., Ashworth, L., Rees, A. B., Tuckett, F.: TephraNZ, Version 1.0, Interdisciplinary Earth Data Alliance (IEDA) [code], 10.26022/IEDA/111724, 2020b.Hopkins, J. L., Lowe, D. J., and Horrocks, J. L.: Tephrochronology in Aotearoa New
Zealand, New Zeal. J. Geol. Geop., 64, 153–200,
10.1080/00288306.2021.1908368, 2021.Houghton, B. F., Wilson, C. J. N., McWilliams, M. O., Lanphere, M. A., Weaver,
S. D., Briggs, R. M., and Pringle, M. S.: Chronology and dynamics of a large
silicic magmatic system: central Taupo Volcanic Zone, New
Zealand, Geology, 23, 13–16, 1995.Howorth, R.: New formations of late Pleistocene tephras from the Okataina
Volcanic Centre,
New Zealand, New Zeal. J. Geol. Geop., 18, 683–712, 1975.Hunt, J. B., Fannin, N. G., Hill, P. G., and Peacock, J. D.: The tephrochronology
and radiocarbon dating of North Atlantic, Late-Quaternary sediments: an
example from the St. Kilda Basin, Geol. Soc. Ldn. Sp. Pub., 90, 227–248, 1995.Iso, N., Okada, A., Ota, Y., and Yoshikawa, T. Fission-track ages of late
Pleistocene tephra on the Bay of Plenty coast, North Island, New
Zealand, New Zeal. J. Geol. Geop., 25, 295–303, 1982.Jarosewich, E., Nelen, J. A., and Norberg, J. A.: Reference samples for electron
microprobe analysis, Geostandard. Newslett., 4, 43–47, 1980.Jochum, K. P., Stoll, B., Herwig, K., Willbold, M., Hofmann, A. W., Amini, M.,
Aarburg, S., Abouchami, W., Hellebrand, E., Mocek, B., and Raczek, I.:
MPI-DING reference glasses for in situ microanalysis: New reference values
for element concentrations and isotope ratios, Geochem. Geophy.
Geosy., 7, 10.1029/2005GC001060, 2006.Jurado-Chichay, Z. and Walker, G. P. L.: Stratigraphy and dispersal of the
Mangaone Subgroup
pyroclastic deposits, Okataina Volcanic Centre, New Zealand, J. Volc. Geoth.
Res., 104, 319–380, 2000.Kassambara, A. and Mundt, F.: factoextra: Extract and Visualize the Results
of Multivariate Data Analyses. R package version 1.0.7, available at:
https://CRAN.R-project.org/package=factoextra (last access: June 2021), 2020.Kilgour, G. N. and Smith, R. T.: Stratigraphy, dynamics, and eruption impacts
of the dual magma Rotorua eruptive episode, Okataina Volcanic Centre, New
Zealand, New Zeal. J. Geol. Geop., 51, 367–378, 2008.Klemetti, E. W., Deering, C. D., Cooper, K. M., and Roeske, S. M.: Magmatic
perturbations in the
Okataina Volcanic Complex, New Zealand at thousand-year timescales recorded
in single zircon crystals, Earth Planet Sc. Lett., 305, 185–194, 2011.Knott, J. R., Sarna-Wojcicki, A. M., Montañez, I. P., and Wan, E.:
Differentiating the Bishop ash bed and related tephra layers by
elemental-based similarity coefficients of volcanic glass shards using
solution inductively coupled plasma-mass spectrometry (S-ICP-MS), Quatern.
Int., 166, 79–86, 2007.Kobayashi, T., Nairn, I., Smith, V., and Shane, P.: Proximal stratigraphy and
event sequence of the c. 5600 cal yr BP Whakatane rhyolite eruption episode
from Haroharo volcano, Okataina Volcanic Centre, New Zealand, New Zeal. J.
Geol. Geop., 48, 471–490, 2005.Kuehn, S. C., Froese, D. G., Carrara, P. E., Foit, F. F., Pearce, N. J., and
Rotheisler, P.: The latest Pleistocene Glacier Peak tephra set revisited and
revised: Major-and trace-element characterization, distribution, and a new
chronology in western North America, Quaternary Res., 71, 201–216, 2009.Kuehn, S. C., Froese, D. G., Shane, P. A. R., and INTAV Intercomparison
Participants: The INTAV intercomparison of electron-beam microanalysis of
glass by tephrochronology laboratories: results and recommendations, Quatern.
Int., 246, 19–47, 2011.Kurbatov, A., Dunbar, N. W., Iverson, N. A., Gerbi, C. C., Yates, M. G.,
Kalteyer, D., and McIntosh, W. C.: Antarctic Tephra Database (AntT), in: AGU
Fall Meeting Abstracts, available at:
http://www.tephrochronology.org/AntT/ (last access: June 2021), December 2014.Le Maitre, R. W.: A proposal by the IUGS Subcommission on the Systematics of
Igneous Rocks for a chemical classification of volcanic rocks based on the
total alkali silica (TAS) diagram: (on behalf of the IUGS Subcommission on
the Systematics of Igneous Rocks), Aus. J. Earth Sci., 31, 243–255,
1984.Leahy, K.: Discrimination of reworked pyroclastics from primary tephra-fall
tuffs: a case study using kimberlites of Fort a la Corne, Saskatchewan,
Canada, Bull. Volc., 59, 65–71, 1997.Lowe, D. J.: Late Quaternary volcanism in New Zealand: towards an integrated
record using distal airfall tephras in lakes and bogs, J. Quaternart Sci., 3, 111–120, 1988.Lowe, D. J.: Tephrochronology and its application: a review, Quat.
Geochronol., 6, 107–153, 2011.Lowe, D. J.: Marine tephrochronology: a personal perspective, Geol. Soc. Ldn.
Sp. Pub., 398, 7–19, 2014.Lowe, D. J.: Using soil stratigraphy and tephrochronology to understand the
origin, age, and classification of a unique Late Quaternary tephra-derived
Ultisol in Aotearoa New Zealand, Quaternary, 2, 9 pp.,
10.3390/quat2010009, 2019.Lowe, D. J. and Newnham, R. M.: Role of tephra in dating Polynesian settlement
and impact, New Zealand, Past Global Changes, 12, 5–7, 2004.Lowe, D. J., Newnham, R. M., and Ward, C. M.: Stratigraphy and chronology of a 15
ka sequence of multi-sourced silicic tephras in a montane peat bog, eastern
North Island, New Zealand, New Zeal. J. Geol. Geop., 42, 565–579,
1999.Lowe, D. J., Tippett, J. M., Kamp, P. J., Liddell, I. J., Briggs, R. M., and
Horrocks, J. L.: Ages on weathered Plio-Pleistocene tephra sequences, western
North Island, New Zealand, Les Dossiers de l'Archéo-Logis, 1, 45–60,
2001.Lowe, D. J., Shane, P. A., Alloway, B. V., and Newnham, R. M.: Fingerprints and
age models for widespread New Zealand tephra marker beds erupted since
30,000 years ago: a framework for NZ-INTIMATE, Quaternary Sci.
Rev., 27, 95–126, 2008.Lowe, D. J., Blaauw, M., Hogg, A. G., and Newnham, R. M.: Ages of 24 widespread
tephras erupted since 30,000 years ago in New Zealand, with re-evaluation of
the timing and palaeoclimatic implications of the Lateglacial cool episode
recorded at Kaipo bog, Quaternary Sci. Rev., 74, 170–194, 2013.Lowe, D. J., Pearce, N. J. G., Jorgensen, M. A., Kuehn, S. C., Tryon, C. A., and
Hayward, C. L.: Correlating tephras and cryptotephras using glass
compositional analyses and numerical and statistical methods: review and
evaluation, Quaternary Sci. Rev., 175, 1–44, 2017.Lowe, D. J., Rees, A. B. H., Newnham, R. M., Hazell, Z. J., Gehrels, M. J.,
Charman, D. J., and Amesbury, M. J.: Isochron-informed Bayesian age modelling
for tephras and cryototephras, and application to mid-Holocene Tuhua tephra,
New Zealand, 20th INQUA Congress, Dublin, 25–31 July 2019 (abstract P-4604,
p. 1), 2019.Manning, D. A.: Middle-late Pleistocene tephrostratigraphy of the eastern Bay
of Plenty, New Zealand, Quatern. Int., 34, 3–12, 1996.Mahony, S. H., Barnard, N. H., Sparks, R. S. J., and Rougier, J. C.: VOLCORE, a
global database of visible tephra layers sampled by ocean
drilling, Sci. Data, 7, 1–17, 2020.McDonough, W. F. and Sun, S. S.: The composition of the Earth, Chem.
Geol., 120, 223–253, 1995.Milner, D. M., Cole, J. W., and Wood, C. P.: Mamaku Ignimbrite: a caldera-forming
ignimbrite erupted from a compositionally zoned magma chamber in Taupo
Volcanic Zone, New Zealand, J. Volcanol. Geoth. Res., 12, 243–264,
2003.Molloy, C., Shane, P., and Augustinus, P.: Eruption recurrence rates in a
basaltic volcanic field based on tephra layers in maar sediments:
implications for hazards in the Auckland volcanic field, Geol. Soc. Am.
Bull., 121, 1666–1677, 2009.Molloy, C. M.: Tephrostratigraphy of the Auckland Maar Craters, MSc thesis,
University of Auckland, Auckland, New Zealand, 2008.Mortimer, N. and Scott, J. M.: Volcanoes of Zealandia and the Southwest
Pacific, New Zeal. J. Geol. Geop., 63, 371–377, 2020.Nairn, I. A.: The Te Rere and Okareka eruptive episodes — Okataina Volcanic
Centre, Taupo Volcanic Zone, New Zealand, New Zeal. J. Geol. Geop., 35, 93–108, 1992.Nairn, I. A.: Geology of the Okataina Volcanic Centre, scale 1: 50 000,
Institute of Geological and Nuclear Sciences geological map 25, 1 sheet+
156 pp., Institute of Geological and Nuclear Sciences Ltd, 2002.Nairn, I. A. and Kohn, B. P.: Relation of the Earthquake Flat Breccia to the
Rotoiti Breccia, central North Island, New Zealand, New Zeal. J. Geol.
Geop., 16, 269–279, 1973.Nairn, I. A., Shane, P. R., Cole, J. W., Leonard, G. J., Self, S., and Pearson,
N.: Rhyolite magma processes of the∼ AD 1315 Kaharoa eruption episode,
Tarawera volcano, New Zealand, J. Volcanol. Geoth. Res., 131, 265–294, 2004.Naish, T. and Kamp, P. J.: Pliocene-Pleistocene marine cyclothems, Wanganui
Basin, New Zealand: A lithostratigraphic framework, New Zeal. J. Geol.
Geop., 38, 223–243, 1995.Naish, T. and Kamp, P. J.: Foraminiferal depth palaeoecology of Late Pliocene
shelf sequences and systems tracts, Wanganui Basin, New Zealand, Sediment.
Geol., 110, 237–255, 1997.Naish, T., Kamp, P. J., Alloway, B. V., Pillans, B., Wilson, G. S., and
Westgate, J. A.: Integrated tephrochronology and magnetostratigraphy for
cyclothemic marine strata, Whanganui Basin: implications for the
Pliocene-Pleistocene boundary in New Zealand, Quatern. Int., 34, 29–48,
1996.Naish, T. R., Field, B. D., Zhu, H., Melhuish, A., Carter, R. M., Abbott, S. T.,
Edwards, S., Alloway, B. V., Wilson, G. S., Niessen, F., and Barker, A.:
Integrated outcrop, drill core, borehole and seismic stratigraphic
architecture of a cyclothemic, shallow-marine depositional system, Wanganui
Basin, New Zealand, J. Royal Soc. New Zeal., 35, 91–122, 2005.Nelson, C. S., Froggatt, P. C., and Gosson, G. J.: Nature, chemistry, and origin
of late Cenozoic megascopic tephras in Leg 90 cores from the southwest
Pacific, in: Proceedings of
the Ocean Drilling Program, Initial Reports, edited by: Kennett, J. P. and Von Der Borch, C. C., 90, Ocean Drilling Program,
Texas A & M University, College Station, TX, 1160–1173, 1985.Newnham, R. M., De Lange, P. J., and Lowe, D. J.: Holocene vegetation, climate
and history of a raised bog complex, northern New Zealand based on
palynology, plant macrofossils and tephrochronology, Holocene, 5, 267–282, 1995.Newnham, R. M., Lowe, D. J., McGlone, M. S., Wilmshurst, J. M., and Higham,
T. F. G.: The Kaharoa Tephra as a critical datum for earliest human impact in
northern New Zealand, J. Archae. Sci., 25, 533–544, 1998.Newnham, R. M., Eden, D. N., Lowe, D. J., and Hendy, C. H.: Rerewhakaaitu Tephra,
a land–sea marker for the Last Termination in New Zealand, with
implications for global climate change, Quaternary Sci. Rev., 22, 289–308, 2003.Newnham, R. M., Lowe, D. J., Green, J. D., Turner, G. M., Harper, M. A., McGlone,
M. S., Stout, S. L., Horie, S., and Froggatt, P. C.: A discontinuous ca. 80 ka
record of Late Quaternary environmental change from Lake Omapere, Northland,
New Zealand, Palaeogeogr. Palaeocl., 207, 165–198, 2004.Newnham, R. M., Vandergoes, M. J., Garnett, M. H., Lowe, D. J., Prior, C., and
Almond, P. C.: Test of AMS 14C dating of pollen concentrates using
tephrochronology, J. Quaternary Sci., 22, 37–51, 2007.Newnham, R. M., Hazell, Z. J., Charman, D. J., Lowe, D. J., Rees, A. B. H.,
Amesbury, M. J., Roland, T. P., Gehrels, M. J., van den Bos, V., and Jara, I. A.:
Peat humification records from Restionaceae bogs in northern New Zealand as
potential indicators of Holocene precipitation, seasonality, and ENSO,
Quaternary Sci. Rev., 218, 378–394, 2019.Newton, A.: Tephrabase, A tephrochronological database, Quaternary
Newsletter, 8–13, available at: https://www.tephrabase.org/ (last access: June 2021), 1996.Nicol, A., VanDissen, R., Vella, P., Alloway, B., and Melhuish, A.: Growth of
contractional structures during the last 10 my at the southern end of the
emergent Hikurangi forearc basin, New Zealand, New Zeal. J. Geol.
Geop., 45, 365–385, 2002.Oksanen, J., Guillaume Blanchet, F., Friendly, M., Kindt, R., Legendre, P.,
McGlinn, D., Minchin, P. R., O'Hara, R. B., Simpson, G. L., Solymos, P., Henry,
M., Stevens, H., Szoecs, E., and Wagner, H.: vegan: Community Ecology Package. R
package version 2.5-6, available at: https://CRAN.R/project.org/package=vegan (last access: June 2021), 2019.Orpin, A. R., Carter, L., Page, M. J., Cochrn, U. A., Trustrum, N. A., Gomez,
B., Palmer, A. S., Mildenhall, D. C., Rogers, K. M., Brackly, H. L., and
Northcote, L.: Holocene sedimentary record from Lake Tutira: a template for
upland watershed erosion proximal to the Waipaoa Sedimentary System,
northeastern New Zealand, Mar. Geol., 270, 11–29, 2010.Pain, C. F.: Some tephra deposits in the south-west Waikato area, North
Island, New Zealand, New Zeal. J. Geol. Geop., 18, 541–550, 1975.Paton, C., Hellstrom, J., Paul, B., Woodhead, J., and Hergt, J.: Iolite:
Freeware for the visualisation and processing of mass spectrometric data, J.
Anal. At. Spec., 26, 2508–2518, 2011.Pearce, N. J.: Towards a protocol for the trace element analysis of glass from
rhyolitic shards in tephra deposits by laser ablation ICP-MS, J. Quaternary
Sci., 29, 627–640, 2014.Pearce, N. J., Westgate, J. A., and Perkins, W. T.: Developments in the analysis
of volcanic glass shards by laser ablation ICP-MS: quantitative and single
internal standard-multielement methods, Quatern. Int., 34, 213–227, 1996.Pearce, N. J., Eastwood, W. J., Westgate, J. A., and Perkins, W. T.: Trace-element
composition of single glass shards in distal Minoan tephra from SW
Turkey, J. Geol. Soc., 159, 545–556, 2002.Pearce, N. J., Westgate, J. A., Perkins, W. T., and Preece, S. J.: The application
of ICP-MS methods to tephrochronological problems, Appl. Geochem., 19, 289–322, 2004.Pearce, N. J., Denton, J. S., Perkins, W. T., Westgate, J. A., and Alloway, B. V.:
Correlation and characterisation of individual glass shards from tephra
deposits using trace element laser ablation ICP-MS analyses: current status
and future potential, J. Quaternary Sci., 22, 721–736, 2007.Pearce, N. J., Alloway, B. V., and Westgate, J. A.: Mid-Pleistocene silicic
tephra beds in the Auckland region, New Zealand: their correlation and
origins based on the trace element analyses of single glass shards, Quatern.
Int., 178, 16–43, 2008.Pearce, N. J., Perkins, W. T., Westgate, J. A., and Wade, S. C.: Trace-element
microanalysis by LA-ICP-MS: the quest for comprehensive chemical
characterisation of single, sub-10 µm volcanic glass shards, Quatern.
Int., 246, 57–81, 2011.Pecher, I. A., Barnes, P. M., LeVay, L. J., and the Expedition 372 Scientists:
Expedition 372 Preliminary Report: Creeping Gas Hydrate Slides and Hikurangi
LWD, International Ocean Discovery Program, available at: 10.14379/iodp.pr.372.2018, 2018.Peti, L., Gadd, P. S., Hopkins, J. L., and Augustinus, P. C.: Itrax μ-XRF
core scanning for rapid tephrostratigraphic analysis: a case study from the
Auckland Volcanic Field maar lakes, J. Quaternary Sci., 35, 54–65, 2020.Peti, L., Hopkins, J. L., and Augustinus, P.: Revised tephrochronology for key
tephras in the 130-ka Ōrākei Basin maar core, Auckland Volcanic
Field, New Zealand: implications for the timing of climatic changes, New
Zealand, New Zeal. J. Geol. Geop., 64, 235–249,
10.1080/00288306.2020.1867200, 2021.Pillans, B.: Direct marine-terrestrial correlations, Wanganui Basin, New
Zealand: the last 1 million years, Quaternary Sci. Rev., 13, 189–200,
1994.Pillans, B.: Quaternary stratigraphy of Whanganui Basin – a globally
significant archive, in: Landscape and quaternary environmental change in New
Zealand, Atlantis Press, Paris, 141–170, 2017.Pillans, B., Alloway, B., Naish, T., Westgate, J., Abbott, S., and Palmer, A.
Silicic tephras in Pleistocene shallow-marine sediments of Wanganui Basin,
New Zealand, J. Royal Soc. New Zeal., 35, 43–90, 2005.Pillans, B. J., Roberts, A. P., Wilson, G. S., Abbott, S. T., and Alloway, B. V.:
Magnetostratigraphic, lithostratigraphic and tephrostratigraphic constraints
on Lower and Middle Pleistocene sea-level changes, Wanganui Basin, New
Zealand, Earth Planet Sc. Lett., 121, 81–98, 1994.
Pillans, B., Kohn, B. P., Berger, G., Froggatt, P., Duller, G., Alloway, B. and Hesse, P.: Multi-method dating comparison for mid-Pleistocene Rangitawa tephra, New Zealand, Quaternary. Sci. Rev., 15, 641–653, 1996.Pittari, A., Prentice, M. L., McLeod, O. E., Yousefzadeh, E., Kamp, P. J. J., Danišík, M., and Vincent, K. A.: Inception of the modern North Island (New Zealand) volcanic setting: spatio-temporal patterns of volcanism between 3.0 and 0.9 Ma, New Zeal. J. Geol. Geop., 64, 250–272, 10.1080/00288306.2021.1915343, 2021.Portnyagin, M. V., Ponomareva, V. V., Zelenin, E. A., Bazanova, L. I., Pevzner, M. M., Plechova, A. A., Rogozin, A. N., and Garbe-Schönberg, D.: TephraKam: geochemical database of glass compositions in tephra and welded tuffs from the Kamchatka volcanic arc (northwestern Pacific), Earth Syst. Sci. Data, 12, 469–486, 10.5194/essd-12-469-2020, 2020.Preece, S. J., Westgate, J. A., Froese, D. G., Pearce, N. J. G., and Perkins, W. T.:
A catalogue of late Cenozoic tephra beds in the Klondike goldfields, Yukon.
Can. J. Earth Sci., 48, 1386–1418, 2011.R Core Team, R: A language and environment for statistical computing, R
Foundation for Statistical Computing, Vienna, Austria, available at:
https://www.R-project.org (last access: June 2021), 2019.Rees, C., Palmer, J., and Palmer, A.: Plio-Pleistocene geology of the lower
Pohangina valley, New Zealand, New Zeal. J. Geol. Geop., 61, 44–63,
2018.Rees, C., Palmer, A., and Palmer, J.: Quaternary sedimentology and
tephrostratigraphy of the lower Pohangina Valley, New Zealand, New Zeal. J.
Geol. Geop., 62, 171–194, 2019.Rees, C., Palmer, J., and Palmer, A.: Tephrostratigraphic constraints on
sedimentation and tectonism in the Whanganui Basin, New Zealand, New Zeal.
J. Geol. Geop., 63, 262–280, 2020.Rosenberg, M. D., Wilson, C. J. N., Bignall, G., Ireland, T. R., Sepulveda, F.,
and Charlier, B. L. A. Structure and evolution of the Wairakei–Tauhara
geothermal system (Taupo Volcanic Zone, New Zealand) revisited with a new
zircon geochronology, J. Volcanol. Geoth. Res., 390, 106705, 10.1016/j.jvolgeores.2019.106705, 2020.Rubin, A. E., Cooper, K. M., Leever, M., Wimpenny, J., Deering, C., Rooney,
T., Gravley, D., and Yin,
Q.-Z.: Changes in magma storage conditions following caldera collapse at
Okataina
Volcanic Center, New Zealand, Contrib. Mineral. Petr., 171, 1–18, 2016.Saffer, D. M., Wallace, L. M., Petronotis, K., and the Expedition 375
Scientists: Expedition 375 Preliminary Report: Hikurangi Subduction Margin
Coring and Observatories, International Ocean Discovery Program,
10.14379/iodp.pr.375.2018, 2018.Sahetapy-Engel, S., Self, S., Carey, R. J., and Nairn, I. A.: Deposition and
generation of multiple widespread fall units from the c. AD 1314 Kaharoa
rhyolitic eruption, Tarawera, New Zealand. Bull. Volc., 76, 836,
10.1007/s00445-014-0836-4, 2014.Sandiford, A., Horrocks, M., Newnham, R., Ogden, J., and Alloway, B.
Environmental change during the last glacial maximum (c. 25000-c. 16500
years BP) at Mt Richmond, Auckland Isthmus, New Zealand, J. Royal Soc. New
Zeal., 32, 155–167, 2002.Sarna-Wojcicki, A. M.: Tephrochronology, in: Quat Geochronol. Methods and Applications, edited by: Noller, J. S., Sowers, J. M., and
Lettis, W. R., AGU
Reference Shelf, American Geophysical Union Washington, DC,
Vol. 4, 357–377, 2000.Saul, G., Naish, T. R., Abbott, S. T. and Carter, R. M.: Sedimentary cyclicity
in the marine Pliocene-Pleistocene of the Wanganui basin (New Zealand):
Sequence stratigraphic motifs characteristic of the past 2.5 my, Geol. Soc.
Am. Bull., 111, 524–537, 1999.Schneider, J. L., Le Ruyet, A., Chanier, F., Buret, C., Ferrière, J.,
Proust, J. N., and Rosseel, J. B.: Primary or secondary distal volcaniclastic
turbidites: how to make the distinction? An example from the Miocene of New
Zealand (Mahia Peninsula, North Island), Sediment. Geol., 145, 1–22,
2001.Seward, D.: Tephrostratigraphy of the marine sediments in the Wanganui Basin,
New Zealand, New Zeal. J. Geol. Geop., 19, 9–20, 1976.Shane, P. A. R.: A widespread, early Pleistocene tephra (Potaka tephra, 1 Ma)
in New Zealand: character, distribution, and implications, New Zeal. J.
Geol. Geop., 37, 25–35, 1994.Shane, P. A. R.: Correlation of rhyolitic pyroclastic eruptive units from the
Taupo volcanic zone by Fe–Ti oxide compositional data, Bull. Volc., 60, 224–238, 1998.Shane, P. A. R.: Tephrochronology: a New Zealand case study, Earth Sci. Rev.,
49, 223–259, 2000.Shane, P. A. R. and Froggatt, P. C.: Glass chemistry, paleomagnetism, and
correlation of middle Pleistocene tuffs in southern North Island, New
Zealand, and Western Pacific, New Zeal. J. Geol. Geop., 34, 203–211,
1991.Shane, P. A. R. and Hoverd, J.: Distal record of multi-sourced tephra in
Onepoto Basin, Auckland, New Zealand: implications for volcanic chronology,
frequency and hazards, Bull. Volc., 64, 441–454, 2002.Shane, P. A. R., Black, T. J., and Westgate, J. A.: Isothermal plateau
fission-track age for a paleomagnetic excursion in the Mamaku Ignimbrite,
New Zealand, and implications for Late Quaternary stratigraphy, Geophys.
Res. Lett., 21, 1695–1698, 1994.Shane, P. A. R., Froggatt, P., Black, T., and Westgate, J.: Chronology of
Pliocene and Quaternary bioevents and climatic events from fission-track
ages on tephra beds, Wairarapa, New Zealand, Earth Planet Sc.
Lett., 130, 141–154, 1995.Shane, P. A. R, Black, T. M., Alloway, B. V., and Westgate, J. A.: Early to middle
Pleistocene tephrochronology of North Island, New Zealand: Implications for
volcanism, tectonism, and paleoenvironments, Geol. Soc. Am. Bull., 108, 915–925, 1996.Shane, P., Lian, O. B., Augustinus, P., Chisari, R., and Heijnis, H.:
Tephrostratigraphy and geochronology of a ca. 120 ka terrestrial record at
Lake Poukawa, North Island, New Zealand, Global Planet.
Change, 33, 221–242, 2002.Shane, P. A. R., Smith, V. C., Lowe, D. J., and Nairn, I. A.: Re-identification of
c. 15700 cal yr BP tephra bed at Kaipo Bog, eastern North Island:
implications for dispersal of Rotorua and Puketarata tephra beds, New Zeal.
J. Geol. Geop., 46, 591–596, 2003a.Shane, P. A. R., Smith, V. C., and Nairn, I. A.: Biotite composition as a tool for
the identification of Quaternary tephra beds, Quaternary Res., 59, 262–270, 2003b.Shane, P. A. R., Smith, V. C., and Nairn, I. A.: High temperature rhyodacites of
the 36 ka Hauparu pyroclastic eruption, Okataina Volcanic Centre, New
Zealand: change in a silicic magmatic system following caldera collapse, J.
Volcanol. Geoth. Res., 147, 357–376, 2005.Shane, P. A. R., Sikes, E. L., and Guilderson, T. P.: Tephra beds in deep-sea
cores off northern New Zealand: implications for the history of Taupo
volcanic zone, Mayor Island and White Island volcanoes, J. Volcanol. Geoth.
Res., 154, 276–290, 2006.Shane, P., Nairn, I. A., Martin, S. B., and Smith, V. C.: Compositional
heterogeneity in tephra deposits resulting from the eruption of multiple
magma bodies: implications for tephrochronology, Quatern. Int., 178, 44–53, 2008.Shane, P., Gehrels, M., Zawalna-Geer, A., Augustinus, P., Lindsay, J., and
Chaillou, I.: Longevity of a small shield volcano revealed by crypto-tephra
studies (Rangitoto volcano, New Zealand): change in eruptive behavior of a
basaltic field, J. Volcanol. Geoth. Res., 257, 174–183, 2013.Smith, V. C., Shane, P., and Smith, I. E. M.: Tephrostratigraphy and geochemical
fingerprinting of the Mangaone Subgroup tephra beds, Okataina volcanic
centre, New Zealand, New Zeal. J. Geol. Geop., 45, 207–219, 2002.Smith, V. C., Shane, P., and Nairn, I. A.: Reactivation of a rhyolite magma body
by new rhyolitic intrusion before the 15.8 ka Rotorua eruptive episode:
implications for magma storage in the Okataina Volcanic Centre, New Zealand.
J. Geol. Soc. Ldn., 161, 757–772, 2004.Smith, V. C., Shane, P., and Nairn, I. A.: Trends in rhyolite geochemistry,
mineralogy, and magma storage during the last 50 kyr at Okataina and Taupo
volcanic centres, Taupo Volcanic Zone, New Zealand, J. Volcanol. Geoth.
Res., 148, 372–406, 2005.Stokes, S., Lowe, D. J., and Froggatt, P. C.: Discriminant function analysis and
correlation of late Quaternary rhyolitic tephra deposits from Taupo and
Okataina volcanoes, New Zealand, using glass shard major element
composition, Quatern. Int., 13–14, 103–117, 1992.Streck, M. J. and Wacaster, S.: Plagioclase and pyroxene hosted melt
inclusions in basaltic andesites of the current eruption of Arenal volcano,
Costa Rica, J. Volcanol. Geoth. Res., 157, 236–253, 2006.Storm, S., Schmitt, A. K., Shane, P., and Lindsay, J. M.: Zircon trace element
chemistry at submicrometer resolution for Tarawera volcano, New Zealand, and implications
for rhyolite 1061 magma evolution, Contrib. Mineral. Petr., 167, 1000,
10.1007/s00410-014-1000-z, 2014.Sutton, A. N., Blake, S., Wilson, C. J., and Charlier, B. L.: Late Quaternary
evolution of a hyperactive rhyolite magmatic system: Taupo volcanic centre,
New Zealand, J. Geol. Soc., 157, 537–552, 2000.Tanaka, H. G. M. T., Turner, G. M., Houghton, B. F., Tachibana, T., Kono, M., and
McWilliams, M. O.: Palaeomagnetism and chronology of the central Taupo
volcanic zone, New Zealand, Geophys. J. Int., 124, 919–934, 1996.Tapia, C. A., Grant, G. R., Turner, G. M., Sefton, J. P., Naish, T. R., Dunbar,
G., and Ohneiser, C.: High-resolution magnetostratigraphy of mid-Pliocene
(3.3–3.0 Ma) shallow-marine sediments, Whanganui Basin, New Zealand, Geophys.
J. Int., 217, 41–57, 2019.Tryon, C. A., Logan, M. A. V., Mouralis, D., Kuhn, S., Slimak, L., and
Balkan-Atlı, N. Building a tephrostratigraphic framework for the
Paleolithic of Central Anatolia, Turkey, J. Archae. Sci., 36, 637–652,
2009.Tryon, C. A., Faith, J. T., Peppe, D. J., Fox, D. L., McNulty, K. P., Jenkins,
K., Dunsworth, H., and Harcourt-Smith, W.: The Pleistocene archaeology and
environments of the Wasiriya beds, Rusinga Island, Kenya, J. Human
Evol., 59, 657–671, 2010.Turner, M. B., Bebbington, M. S., Cronin, S. J., and Stewart, R. B.: Merging
eruption datasets: building an integrated Holocene eruptive record for Mt
Taranaki, New Zealand, Bull. Volc., 71, 903–918, 2009.Turner, M. B., Cronin, S. J., Bebbington, M. S., Smith, I. E., and Stewart, R. B.:
Integrating records of explosive and effusive activity from proximal and
distal sequences: Mt. Taranaki, New Zealand, Quatern. Int., 246, 364–373, 2011.Turney, C. S., Blockley, S. P., Lowe, J. J., Wulf, S., Branch, N. P.,
Mastrolorenzo, G., Swindle, G., Nathan, R., and Pollard, A. M.: Geochemical
characterization of Quaternary tephras from the Campanian Province,
Italy, Quatern. Int., 178, 288–305, 2008.Vandergoes, M. J., Hogg, A. G., Lowe, D. J., Newnham, R. M., Denton, G. H.,
Southon, J., Barrell, D. J., Wilson, C. J., McGlone, M. S., Allan, A. S., and
Almond, P. C.: A revised age for the Kawakawa/Oruanui tephra, a key marker for
the Last Glacial Maximum in New Zealand, Quaternary Sci. Rev., 74, 195–201, 2013.Venables, W. N. and Ripley, B. D.: Modern Applied Statistics With S, 4th
Edn., Springer-Verlag, New York, 2002.Vu, V. Q.: ggbiplot: A ggplot2 based biplot, R package version 0.55, available at:
http://github.com/vqv/ggbiplot (last access: June 2021), 2011.Vucetich, C. G. and Pullar, W. A.: Stratigraphy and chronology of late
Pleistocene volcanic ash beds in the central North Island, New Zealand, New
Zeal. J. Geol. Geop., 12, 784–837, 1969.
Vucetich, C. G., Birrell, K. S., and Pullar, W. A.: Ohinewai Tephra Formation; a
c. 150000-year-old tephra marker in New Zealand, New Zeal. J. Geol.
Geop., 21, 71–73, 1978.Walker, G. P. L.: The Taupo plinian pumice: product of the most powerful known
(ultraplinian) eruption?, J. Volcanol. Geoth. Res., 8, 69–94, 1980.Walker, G. P. L.: Volcanological applications of pyroclastic studies, in: Tephra Studies, edited by: Self,
S. and Sparks, R. S. J., Reidel, Dordrecht,
391–403, 1981.Wallace, K. L.: Alaska Tephra Data, 2018 (ver. 1.0, August 2018): U.S.
Geological Survey data release,
10.5066/P9PFQGVC, available at:
https://avo.alaska.edu/about/tephra.php (last access: June 2021), 2018.Ward, W. T.: Volcanic ash beds of the lower Waikato basin, North Island, New
Zealand, New Zeal. J. Geol. Geop., 10, 1109–1135, 1967.Watkins, N. D. and Huang, T. C.: Tephras in abyssal sediments east of the
North Island, New Zealand: chronology, paleowind velocity, and
paleoexplosivity, New Zeal. J. Geol. Geop., 20, 179–198, 1977.Westgate, J. A. and Gorton, M. P.: Correlation techniques in tephra studies,
in: Tephra studies, Springer, Dordrecht, 73–94, 1981.Westgate, J. A., Perkins, W. T., Fuge, R., Pearce, N. J. G., and Wintle, A. G.:
Trace-element analysis of volcanic glass shards by laser ablation
inductively coupled plasma mass spectrometry: application to
tephrochronological studies, Appl. Geochem., 9, 323–335, 1994.Westgate, J. A., Preece, S. J., Froese, D. G., Pearce, N. J., Roberts, R. G.,
Demuro, M., Hart, W. K., and Perkins, W.: Changing ideas on the identity and
stratigraphic significance of the Sheep Creek tephra beds in Alaska and the
Yukon Territory, northwestern North America, Quatern. Int., 178, 183–209,
2008.Wickham, H.: ggplot2: Elegant Graphics for Data Analysis, Springer-Verlag New
York, 2016.Wilson, C. J. N. and Rowland, J. V.: The volcanic, magmatic and tectonic setting
of the Taupo Volcanic Zone, New Zealand, reviewed from a geothermal
perspective, Geothermics, 59, 168–187, 2016.Wilson, C. J. N., Houghton, B. F., McWilliams, M. O., Lanphere, M. A., Weaver,
S. D. and Briggs, R. M.: Volcanic and structural evolution of Taupo Volcanic
Zone, New Zealand: a review, J. Volcanol. Geoth. Res., 68, 1–28,
1995a.Wilson, C. J. N., Houghton, B. F., Pillans, B. J., and Weaver, S. D.: Taupo
Volcanic Zone calc-alkaline tephras on the peralkaline Mayor Island volcano,
New Zealand: identification and uses as marker horizons, J. Volcanol. Geoth.
Res., 69, 303–311, 1995b.Wilson, C. J. N., Gravley, D. M., Leonard, G. S., and Rowland, J. V.: Volcanism in
the central Taupo Volcanic Zone, New Zealand: tempo, styles and controls,
in: Studies in volcanology: the legacy of George Walker, edited by: Thordarson, T., Self, S., Larsen, G., Rowland, S. K., and Hoskuldsson, A., Special
Publications of IAVCEI (Geological Society, London), 2, 225–247, 2009.