Joel A. Baker

The Kidnappers [∼1200 km³ dense rock equivalent (DRE)] and Rocky Hill (∼200 km³ DRE) caldera-forming events in the Taupo Volcanic Zone, New Zealand, were erupted in close succession from the Mangakino volcanic centre. They have identical radiometric ages at ∼1 Ma, yet erosion along the contact between the two deposits suggests that some years to decades separated the two eruptions. Field constraints and the similarities of crystal textures and compositions and glass chemistries of both eruption deposits demonstrate that they came from one overall magmatic system with a common crystal mush source. However, second-order variations in these parameters confirm that the Kidnappers and Rocky Hill deposits represent distinct events and are not the products of a single zoned magma chamber. The systematically zoned Kidnappers fall deposits provide evidence for the tapping of three discrete magma bodies, whereas the succeeding Kidnappers ignimbrite is compositionally more diverse. The transition from fall to flow deposition marks a change in the style of caldera collapse and the simultaneous evacuation of discrete but compositionally diverse melts, each of which underwent a distinct evolution and was held at slightly different P–T conditions prior to eruption. Contrasting plagioclase and orthopyroxene zonation patterns are present in pumices originating from three discrete magma bodies. Less evolved mafic melts interacted with the system, which mobilized portions of the final erupted melt through heating and volatile or chemical exchange in the mush. The two largest Kidnappers melt-dominant bodies were re-tapped in modified form, or re-established from their common mush source, prior to the Rocky Hill event. Rocky Hill pumices contain common, fluid-affected antecrystic crystal clots derived from chamber wall material. Amphibole compositions from each eruption reflect melt evolution processes and, in particular, the contemporaneous crystallization of biotite and breakdown of orthopyroxene. Plagioclase and orthopyroxene from Rocky Hill pumices share common zonation patterns with those from the two largest magma bodies in the Kidnappers. The rapid production of new melt-dominant bodies and the triggering of the Rocky Hill eruption reflect the ability of the magmatic system to rejuvenate on a geologically short timescale. The Mangakino centre did not follow a typical cycle of decreased activity after the supervolcanic Kidnappers event, instead producing a second caldera-forming eruption, within years to decades from the same system.

Protecting a nation's primary production sector and natural estate is heavily dependent on the ability to determine the risk presented by incursions of exotic insect species. Identifying the geographic origin of such biosecurity breaches can be crucial in determining this risk and directing the appropriate operational responses and eradication campaigns, as well as ascertaining incursion pathways. Reading natural abundance biogeochemical markers using mass spectrometry is a powerful tool for tracing ecological pathways as well as provenance determination of commercial products and items of forensic interest. However, application of these methods to trace insects has been underutilised to date and our understanding in this field is still in a phase of basic development. In addition, biogeochemical markers have never been considered in the atypical situation of a biosecurity incursion, where sample sizes are often small, and of unknown geographic origin and plant host. These constraints effectively confound the interpretation of the one or two isotope geo-location markers systems that are currently used, which are therefore unlikely to achieve the level of provenance resolution required in biosecurity interceptions. Here, a novel approach is taken to evaluate the potential for provenance resolution of insect samples through multiple biogeochemical markers. The international pest, Helicoverpa armigera, has been used as a model species to assess the validity of using naturally occurring δ²H, ⁸⁷Sr/⁸⁶Sr, ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb isotope ratios and trace element concentration signatures from single moth specimens for regional assignment to natal origin. None of the biogeochemical markers selected were individually able to separate moths from the different experimental regions (150–3000 km apart). Conversely, using multivariate analysis, the region of origin was correctly identified for approximately 75% of individual H. armigera samples. The geographic resolution demonstrated with this approach has considerable potential for biosecurity as well as other disciplines including forensics, ecology and pest management.

We present a new technique for the precise determination of platinum (Pt) stable isotope ratios by multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS) using two different Pt double-spikes (¹⁹²Pt–¹⁹⁸Pt and ¹⁹⁶Pt–¹⁹⁸Pt). Results are expressed relative to the IRMM-010 Pt isotope standard as the parts per million difference in ¹⁹⁸Pt/¹⁹⁴PtPt ratios (μ¹⁹⁸Pt). Repeated measurements of the IRMM-010 Pt standard in two different laboratories, consuming ca. 40–85 ng of Pt, show that a long-term external reproducibility for μ¹⁹²Pt of ≤40 ppm (2 sd; equivalent to ≤10 ppm u⁻¹, where u is the unified atomic mass unit) can be obtained on Pt stable isotope ratios with either double-spike. Elemental doping tests reveal that double-spike corrected Pt stable isotope ratios are insensitive to the presence of relatively high (up to 10%) levels of matrix elements, although the ¹⁹²Pt–¹⁹⁸Pt double-spike is affected by an isobaric interference on ¹⁹²Pt from ¹⁹²Os. The ¹⁹⁶Pt–¹⁹⁸Pt double-spike does not use ¹⁹²Pt in the double-spike inversion and is unaffected by Os contamination, and is our recommended double-spike for use with natural samples. As part of this study, we re-determined the natural Pt isotopic composition of IRMM-010 by MC-ICPMS using external element (Pb) doping to correct for instrumental mass bias and have identified relative Pt isotope differences of up to 10% from the reference values for this standard. The new isotopic composition of the IRMM-010 standard (¹⁹⁰Pt = 0.01289%, ¹⁹²Pt = 0.7938%, ¹⁹⁴Pt = 32.81%, ¹⁹⁵Pt = 33.79%, ¹⁹⁶Pt = 25.29% and ¹⁹⁸Pt = 7.308%) results in a redefined Pt atomic weight of 195.08395 ± 0.00068. Using our technique we have measured small, reproducible and statistically significant offsets in Pt stable isotope ratios between different Pt element standards and the IRMM-010 standard, which potentially indicates that natural Pt stable isotope fractionations exist that are larger than the reproducibility of our technique.

The geochemistry of pyroclasts sampled from four volcanoes along the Kermadec arc in the SW Pacific is used to investigate the genesis of silicic magmas in a young (2. At all four volcanoes the trace element patterns of pumice are subparallel to both those of previously erupted basalts and/or whole mafic blebs found both as discrete pyroclasts and as inclusions within pumices. Pb and Sr isotopic compositions have limited ranges within single volcanoes, but vary considerably along the arc, being more radiogenic in the southern volcanoes. Distinctive crystal populations and zonation patterns in pumices, mafic blebs and plutonic xenoliths indicate that many crystals did not grow in the evolved magmas, but are instead mixed from other sources including gabbros and hydrothermally altered tonalites. Such open-system mixing is ubiquitous at the four volcanoes. Oxygen isotope compositions of both phenocrysts (silicic origin) and xenocrysts or antecrysts (mafic origin) are typical for mantle-derived melts. Whole-rock, glass and mineral chemistries are consistent with evolved magmas being generated at each volcano through ∼70–80% crystal fractionation of a basaltic parent. Our results are not consistent with silicic magma generation via crustal anatexis, as previously suggested for these Kermadec arc volcanoes. Although crystallization is the dominant process driving melt evolution in the Kermadec volcanoes, we show that the magmatic systems are open to contributions from both newly arriving melts and wholly crystalline plutonic bodies. Such processes occur in variable proportions between magma batches, and are largely reflected in small-scale chemical variations between eruption units.

The Higashi‐Izu Monogenetic Volcano Field (HIMVF) consists of 70 subaerial monogenetic volcanoes on the northeastern Izu Peninsula, Japan, and 50 submarine monogenetic volcanoes that extend offshore toward Izu‐Oshima on the Izu‐Bonin Arc volcanic front. We investigate olivine‐hosted glassy silicate melt inclusions erupted in scoria from two of the subaerial monogenetic volcanoes, Takatsukayama and Sukumoyama. Major element data (and volatile elements S and Cl) have been collected from 85 inclusions, of which 26 and 41 have been analyzed for trace and volatile (H₂O, CO₂) elements, respectively. The trace element compositions of the melt inclusions, together with those of the whole rocks from volcanoes within the HIMVF, vary systematically across the HIMVF, even over 5 km between Takatsukayama and Sukumoyama. These variations reflect a decrease in the contribution from slab fluids that leads to melting of the mantle with distance from the volcanic front, and increasing subducting slab depth. The Takatsukayama and Sukumoyama inclusions also reveal an intra‐volcano geochemical diversity; most are low TiO₂ (0.81–1.18 wt.%), high Al₂O₃ (15.88–19.34 wt.%) basalts (low TiO₂‐HABs), with a few high TiO₂ (1.11–2.19 wt.%), low Al₂O₃ (11.75–14.04 wt.%) basalts (high TiO₂‐LABs) that are sometimes trapped in the same crystal. As both groups show the cross‐HIMVF geochemical variability, we conclude that the heterogeneity does not reflect mantle processes or the true composition of melts in the magma chambers; instead we relate it to interstitial melts within the crystal mush of the magma chambers experiencing distinct crystallization histories.

Increasing paleoclimatic evidence suggests that the Little Ice Age (LIA) was a global climate change event. Understanding the forcings and associated climate system feedbacks of the LIA is made difficult by the scarcity of Southern Hemisphere paleoclimate records. We use a new glaciochemical record of a coastal ice core from Mt. Erebus Saddle, Antarctica, to reconstruct atmospheric and oceanic conditions in the Ross Sea sector of Antarctica over the past five centuries. The LIA is identified in stable isotope (δD) and lithophile element records, which respectively demonstrate that the region experienced 1.6 ± 1.4 °C cooler average temperatures prior to 1850 AD than during the last 150 yr and strong (>57 m s⁻¹) prevailing katabatic winds between 1500 and 1800 AD. Al and Ti concentration increases of an order of magnitude (>120 ppb Al) are linked to enhanced aeolian transport of complex silicate minerals and represent the strongest katabatic wind events of the LIA. These events are associated with three 12–30 yr intervals of cooler temperatures at ca. 1690 AD, 1770 AD and 1840 AD. Furthermore, ice core concentrations of the biogenic sulphur species MS⁻ suggest that biological productivity in the Ross Sea polynya was ~80% higher prior to 1875 AD than at any subsequent time. We propose that cooler Antarctic temperatures promoted stronger katabatic winds across the Ross Ice Shelf, resulting in an enlarged Ross Sea polynya during the LIA.

New geochemical and isotopic data are presented for volumetrically minor, depleted low-Ti basalts that occur in the Plateau Basalt succession of central East Greenland (CEG), formed during the initial stages of opening of the North Atlantic at 55 Ma. The basalts have mid-ocean ridge basalt (MORB)-like geochemistry (e.g. depleted light rare earth elements) and are distinct from the high-Ti lavas that dominate the sequence. Rare earth element geochemistry implies derivation from a source more depleted than the typical MORB source, and suggests polybaric melting and contributions from both spinel- and garnet-facies mantle. The low-Ti basalts have Sr–Nd–Pb–Hf isotopic characteristics that are similar to those of depleted magmas from Iceland (e.g. Theistareykir) and adjacent ridges (Kolbeinsey and Reykjanes) and distinct from global MORB (e.g. negative Δ²⁰⁷Pb, and Hf and Nd isotope compositions that plot above the mantle reference line). Isotope and trace element data indicate the involvement of two depleted source components. One component has isotopic compositions similar to other depleted components identified in the North Atlantic and has high Rb/Zr and Ba/Nb. The second is isotopically less depleted with lower Rb/Zr and Ba/Nb. Small degrees of crustal contamination (< 1%) by both amphibolitic and granulitic crust result in relatively large changes in isotopic composition (c. 1% lower for ²⁰⁶Pb/²⁰⁴Pb and 0·1% higher for ⁸⁷Sr/⁸⁶Sr depending on the contaminant). Negative ΔNb suggests a MORB affinity for the low-Ti magmas; however, they are distinguished from global normal (N)-MORB on the basis of vertical deviations from the Northern Hemisphere Reference Line (negative Δ²⁰⁷Pb and positive Δ²⁰⁸Pb), and relative enrichments in Ba, Sr and Pb. The isotopic compositions of the low-Ti CEG basalts suggest correlation with modern depleted components beneath Iceland and adjacent ridges, considered to be derived from upper mantle sources polluted by the Iceland plume. However, small positive Pb peaks when normalized to MORB, and lower Nb distinguish the CEG low-Ti basalts from depleted Icelandic compositions. The lower ΔNb (< 0) and ⁸⁷Sr/⁸⁶Sr, and suggestion of higher ²⁰⁶Pb/²⁰⁴Pb in crustally uncontaminated parental melts imply a closer affinity to compositions from the oceanic ridges surrounding Iceland (especially the Reykjanes Ridge), yet they are subtly distinct on the basis of available trace element data. We suggest that this depleted component was an integral part of the plume that melted primarily during the rapid lithospheric uplift and extension associated with continental break-up.