The Carrán-Los Venados volcanic field in southern Chile comprises small basaltic eruption centres of Holocene to historical ages. These centres are atop extensive, basaltic flows that erupted during late glacial or early postglacial times (< 14ka), marking a dramatic change in eruption style over a short space of time. Differences in trace element characteristics and U-series isotopes point to a dampened subduction influence in the melting environment of the older Basal Lavas. Th isotopes point to higher melting rates and more dominant decompression melting, which may be related to the deglaciation of southern Chile at this time. Olivine textures and chemistry suggest longer storage times for the Basal Lavas compared to the Holocene tephras. The historic eruptions have relatively homogeneous whole rock compositions, suggesting the development of a storage system in the lower crust. This may be the beginning of a thermal environment more akin to those of nearby stratovolcanoes.

Partial melting at destructive plate margins is usually linked to fluid addition from the subducting plate, but decompression melting and asymmetric “wet” and “dry” wings of the melting zone at back-arc spreading centres have also been invoked. Distinguishing between these models has proved difficult using conventional geochemical data. Here, we combine 230U–238Th disequilibria, H2O contents and Ba/Nb ratios on glasses to identify fluid-fluxed versus decompression melting across the Tonga Arc – Lau back-arc. From the arc front into the back-arc, (230U/238Th) disequilibria range from 0.55 to 1.14, H2O contents from 2 to 0.25 wt% and Ba/Nb ratios from 1000 to 5. The (230U/238Th) disequilibria and ratios of fluid mobile to immobile trace elements are amongst the most extreme reported from arcs and change to values typical of mid-ocean ridges. Our data provide evidence for the co-existence of both fluid-fluxed and decompression melting regimes and suggest that back-arcs situated close to the arc may be able to draw subduction-related material into the spreading axis. The systematic compositional change with increasing distance between arc and back-arc does not reflect changes in dehydration reaction in the subducting slab, but different proportions of slab material contributing to the back-arc spreading regime. A stepwise change at >100 km distance between arc and back-arc marks the separation between fluid-fluxed and decompression melting domains occurring over relatively short spatial distances. These are also associated with a transitional change in ridge morphology due to the appearance of an axial magma chamber at the southern East Lau Spreading Centre.

The Fui Norte and Fui Sur small eruptive centres, together with the nearby Mocho-Choshuenco Volcanic Complex, are all located within what is potentially the most hazardous segment of the Southern Volcanic Zone of Chile. Developing comprehensive knowledge on the origin of evolution of these systems is not only important to better understanding of small eruptive centres, but also contributes to improved volcanic hazard prediction and mitigation. Using Sr–Nd isotopes, we determined that Fui Norte cluster has an independent plumbing system, while Fui Sur would be genetically related to the Mocho-Choshuenco stratovolcano. Through mixing models, we determined that the isotopic signatures of Fui Norte are closer to a MORB mantle isotopic composition, whereas the products from the Fui Sur cluster and Mocho-Choshuenco volcano exhibit a greater influence from slab components. This result shows that even in spatially constrained areas, magmas can record significant source differences. Using petrographic information and diffusion chronometry, we determined crustal timescales for the Fui Norte and Fui Sur SECs, from 1 month up to 4.5 years. This unexpectedly large time-scale range is interpreted as the lifespan of the crustal reservoir for these small eruptive centres. The significant differences in their source origin and the petrologic approaches reveal that both Fui Norte and Fui Sur have independent magmatic histories at the mid to upper crustal environment under similar timescales. Understanding that these systems operate independently from mantle to crust is relevant for future hazard assessment in the Southern Andes.

The George Fisher and Hilton Zn-Pb-Ag deposits are located approximately 20 km north of Mount Isa. Although previous workers have noted the existence of a dolerite dyke at the Hilton Zn-Pb-Ag deposit (Valenta, 1994b; Valenta, 1994a), a dolerite dyke at the George Fisher Zn-Pb-Ag deposit has not been previously documented. Progressive underground expansion at the George Fisher mine has resulted in the discovery of a dolerite dyke in the southernmost portion of the deposit. The temporal and petrological relationship between the dolerite dykes and the adjacent Zn-Pb-Ag mineralisation at the George Fisher and Hilton Zn-Pb-Ag deposits has not been considered by previous studies, and has significant implications for the currently accepted syn-diagenetic metallogenic model. In assay data, the dolerite dykes correspond with a large spike in TiO2 and V values. In drill core, the dolerite dykes occur as a light grey to grey-brown coloured rock that is commonly overprinted along its margins by Zn-Pb-Ag mineralisation. In-situ U-Pb geochronology performed on igneous apatite produce a lower intercept age of 1611 & PLUSMN; 21 Ma (MSWD = 0.93) and 1619 & PLUSMN; 22 Ma (MSWD = 0.53) for the dolerite dykes at the George Fisher and Hilton deposits, respectively. This age is consistent with dyke intrusion during the earliest phases of deformation during the (1620-1500 Ma) Isan Orogeny. The dolerite dykes have experienced multiple stages of post-emplacement hydrothermal alteration/veining, which have paragenetic equivalents in the adjacent Zn-Pb-Ag orebodies. The hydrothermal stages include: (1) Quartz & PLUSMN; albite & PLUSMN;K-feldspar alteration/veining; (2) Dolomite alteration/veining; (3) Biotite-chlorite-sulphide alteration; (4) Paragenetically late calcite, dolomite and/or sulphide veining. Monazite from a quartz & PLUSMN; albite & PLUSMN;K-feldspar vein in the Hilton dyke produces a lower intercept age of 1513 & PLUSMN; 16 Ma (MSWD = 1.1), constraining the maximum age of alteration within the dolerite dykes. To assess the timing of alteration in the adjacent George Fisher Zn-Pb-Ag deposit, in-situ Lu-Hf geochronology was performed on pre-mineralisation calcite from a section of stratabound Zn-Pb-Ag mineralisation, and a paragenetically late cross-cutting sphalerite-calcite vein. Calcite from the pre-mineralisation alteration assemblage produces a Lu-Hf age of 1501 & PLUSMN; 32 Ma (MSWD = 1.04), which is interpreted to constrain the maximum age of stratabound Zn-Pb-Ag mineralisation. Calcite from the late cross-cutting vein produced a Lu-Hf age of 1289 & PLUSMN; 26 Ma (MSWD = 1.00), which is interpreted to constrain the age of postmineralisation faulting throughout the deposit. The evidence presented in this study indicates that the dolerite dykes intruded during the early Isan Orogeny at ca. 1620 Ma, and experienced subsequent hydrothermal alteration during D3 of the Isan Orogeny coeval with Zn-Pb-Ag mineralisation.

Monogenetic volcanoes are characterised worldwide by a single eruptive phase that is short-lived, with small eruptive volumes that produce a wide range and complexity of landforms. Investigating the evolution in eruptive styles through the active history of a volcano is key to understanding the role of phreatomagmatism in the formation of these complex monogenetic systems. The classification of the complexity of a monogenetic volcanic centre is of great significance to understanding both past volcanoes and the hazards of future volcanoes. Complexity can be defined by the number of volcanic structures created, the presence of multiple types of eruptions, and the number of conduits involved. In this paper we reconstruct the volcanic history of the Waitomokia Volcanic Complex, located in the southern lowlands of the active monogenetic Auckland Volcanic Field (AVF), New Zealand. Activity began with deposition of an initial tuff ring, followed by vent migration and establishment of a maar with a surrounding tuff ring. Four smaller tuff rings developed on the north and northeastern rim of the maar. This was followed by the noteworthy deposition of complex intercalated transitional deposits from at least two tuff rings and magmatic deposits from a scoria cone. Three scoria cones were then built within the maar, followed by minor effusion of short lava flows. Waitomokia highlights the prospect of having a complex system with ten or more landforms being created in different areas active at the same time, with associated eruptive styles and mechanisms. The possibility of a complex eruption, where several styles may occur simultaneously from distinct vents, should be considered in hazard assessment and crisis management plans.

Abstract Copper isotope analysis has emerged as a promising tool for understanding genetic processes in Cu ore deposits. However, applications of this analytical technique to Archean Cu deposits have been extremely limited, even though Archean terranes are among the most economically endowed on Earth. As such, this study presents the first Cu isotope analysis of an Archean Cu deposit, the Mesoarchean Carlow Castle hydrothermal Cu‐Co‐Au deposit. Archean primary Cu sulfide ore samples and Cenozoic supergene Cu ore samples were analyzed. Primary ore samples are isotopically light, with δ65Cu values ranging between −0.80 ± 0.02‰ and 0.00 ± 0.007‰, whilst supergene samples are isotopically heavier and range between −0.50 ± 0.01‰ and 0.62 ± 0.005‰. In primary ore samples, a relationship is observed between the Cu isotope signature, ore grade, and alteration assemblage that records the isotopic and physicochemical evolution of the Carlow Castle deposit's hydrothermal ore‐forming system. A mafic igneous source is suggested as a metal source in the Carlow Castle Cu‐Co‐Au deposit. The limited heavy isotopic fractionation of supergene Cu ore samples in this study is interpreted to reflect limited redox cycling of Cu due to in situ oxidative weathering of vein‐hosted Cu sulfides in the overlying Cenozoic supergene system. This differs from previously studied deposits where significant Cu transport and multiple stages of isotopic enrichment are often evident in supergene Cu enrichment layers. The results of this study suggest that Cu isotope analysis could be valuable in understanding genetic processes in hydrothermal Cu deposits, including Archean ore deposits and terranes.

Osorno volcano (41 degrees 06'S, 72 degrees 20'W) is a composite stratovolcano of the Central Southern Volcanic Zone of the Chilean Andes. It is the southernmost member of a NE-SW trending alignment of volcanic edifices including La Picada and Puntiagudo volcanoes and the Cordon Cenizos chain. According to contemporary descriptions recorded by Charles Darwin in 1835, two eruptive events occurred: the first during January-February, and the second during November-December 1835 and January 1836. The volcano erupted basaltic andesite lavas and tephra fall deposits (52.4 to 52.9 SiO2 wt. %), which contain phenocrysts of olivine, plagioclase, clinopyroxene, and spinel. The compositions of these phenocryst phases, together with those of olivine-hosted melt inclusions, allowed us to constrain intensive parameters for the pre-eruptive magmas. These varied from 1060 degrees C to 1140 degrees C, with an oxygen fugacity buffer of similar to Delta QFM +1.1, dissolved water concentrations of up to 5.6 wt. % (average of similar to 4.2 wt. %) and maximum pressures equivalent to -7-km depth. Textural relations, such as crystal accumulations and clots, zoning in crystals and other indications of disequilibrium, lead us to infer the involvement of a crystal mush, rich in individual crystals and clots of crystals, which underwent a degree of disaggregation and entrainment into the transiting magma prior to eruption. Comparison of trace element abundances, including rare earth elements, fluid-mobile elements, and relatively fluid-immobile elements, combined with Sr-87/Sr-86 and Nd-143/Nd-144 isotope ratios, allows us to consider variations in slab-derived fluid input and the minor role of crustal contamination on the Osorno eruptive products and those from neighboring volcanic systems. Our results suggest both a greater contribution from slab-derived fluid and a higher degree of partial melting in the systems supplying stratovolcanoes (Osorno, Calbuco, and La Picada) relative to those supplying small eruptive centers built over the major regional Liquilie-Ofqui Fault Zone.

Carbonaceous chondritic meteorites are primordial Solar System materials and a source of water delivery to Earth. Fluid flow on the parent bodies of these meteorites is known to have occurred very early in Solar System history (first <4 million years). We analyze short-lived uranium isotopes in carbonaceous chondrites, finding excesses of 234-uranium over 238-uranium and 238-uranium over 230-thorium. These indicate that the fluid-mobile uranium ion U6+ moved within the past few 100,000 years. In some meteorites, this time scale is less than the cosmic-ray exposure age, which measures when they were ejected from their parent body into space. Fluid flow occurred after melting of ice, potentially by impact heating, solar heating, or atmospheric ablation. We favor the impact heating hypothesis, which implies that the parent bodies still contain ice.

Electron microprobe analyses were conducted on volcanic glasses extracted from Holocene tephra marker beds on the Willaumez isthmus in West New Britain, Papua New Guinea. These tephra beds are pivotal in the dating of a wide range of human artefacts and manuports found in the intervening buried soils, extending back over the last 40,000 years. Three major groups can be easily separated: W-K1 and 2; W-K3 and 4; and the Dakataua tephra. Of the remaining post-W-K4 tephras, most show slightly higher FeO and CaO and lower SiO2 contents than the W-K3 and 4 group, although there is some overlap. The combination of these geochemical data sets with the known stratigraphy and radiocarbon dates has helped resolve tephra correlation where these ashes become thin and less visually diagnostic or where pumice has been resorted and redeposited by the Kulu-Dulagi River.

Dazzling, highly retouched obsidian stemmed objects comprised part of the material world of people in West New Britain and beyond in Papua New Guinea sometime between 6000 and 3000 years ago. Geochemical characterisation studies of the region’s obsidian sources indicate that the source of Kutau-Bao dominated to the point where stemmed artefacts made from its obsidian have been found in abundance on nearby Garua Island where another obsidian source, Baki, is located. Furthermore, stemmed artefacts made from Baki obsidian are not found anywhere else except on Garua Island. Studies suggest the nature of production involved centralised knowledge and practices with specialist knappers located on Garua Island. We explore two different approaches in order to look at how such organisation was accomplished. Firstly, we conducted replication experiments to identify characteristic debitage of aspects of stemmed artefact making. Then, the debitage attributes identified were used to examine excavated material from three sites, one near the Kutau-Bao source and two on Garua Island to try to understand the practices employed at the two sources. Our results suggest that Garua Island was a special place where knappers came and used the Baki source to learn, practise and hone their skills for making these dazzling artefacts.

Auckland Volcanic Field (AVF) is a basaltic intraplate volcanic field in North Island, New Zealand, upon which >1.6 million people live. Seismic velocity tomography and geochemistry suggest a primary mantle source region at a depth of 70-90 km. Geochemical analysis indicates a range of magma compositions, and that melts ascend with little crustal interaction. Eruptions generally began with a phreatomagmatic phase forming maar and tuff rings with tephra fall, base surges, and ballistic projectiles as the main hazards. Subsequent magmatic phases formed scoria cones, and sometimes produced lava flows. Ages of 47 of the 53 volcanic centres reveal that the AVF first erupted similar to 193 ka, and last erupted similar to 500 yrs. BP. These geochronological constraints indicate repose periods <= 0.1-13 kyr, which have decreased since similar to 60 ka. From known geological and exposure information, and using an interdisciplinary approach, eight future eruption scenarios have been developed for planning processes. Outstanding questions for the AVF concern the cause of mantle melting, the structure of the underlying lithosphere, magma ascent rates, controls on repose periods and eruptive volumes. Answering these questions may improve our understanding of warning periods, monitoring strategies, spatiotemporal risk profiles, and socio-economic impacts of volcanism on New Zealand's largest city.

Injection of volatile-rich mafic magma prior to an eruption may trigger episodes of volcanism and can act to transfer metals from depth. However, petrologic knowledge of the timescales from mafic injection to eruption have thus far been focussed on mineral-scale studies of chemical zoning patterns. The study of mafic enclaves dispersed within eruption products can provide insights into the interaction between deep and shallow reservoirs. We combine 238 U-230 Th-226 Ra-210 Pb isotope data with trace element concentrations across the interface of two contrasting mafic enclaves in contact with their host andesite from the 2010 eruption at Soufrière Hills Volcano (SHV), Montserrat to investigate the history of mass exchange between the mafic enclave and the andesite host. The application of these time-sensitive isotopes highlights complexities in the transfer of volatiles and metal elements between magmas and the enclaves’ potential as eruption triggers. The enclaves exhibit ( 210 Pb/ 226 Ra) 0 ratios > 1 consistent with volatile input to the subsurface plumbing system a few decades prior to eruption. Samples of the andesitic host, however, which make up the bulk of the eruptive products, have ( 210 Pb/ 226 Ra) 0 ≤ 1 suggesting no net volatile gain in the decades leading up to eruption, or that melt-volatile interaction is on a timescale unresolvable by 210 Pb-226 Ra systematics (i.e. <2 years). Variations in trace elements such as Cu, Pb and Ba show loss of a magmatic volatile phase and transport of metals within the deeper part of the plumbing system during differentiation of magmas feeding SHV. Our results do not support that volatile transfer into the andesite via enclaves is a direct trigger of explosive eruptions although the enclaves are likely syn-eruptively formed. 238 U-230 Th-226 Ra-210 Pb and trace element systematics at SHV support a role for fresh magma influx during periods of unrest, but long-term accumulation of the andesite.

The Auckland Volcanic Field (AVF) is one of the most intensively studied monogenetic basalt fields in the world yet its origin remains enigmatic. Magmatism in the AVF occurred from ~193 ka to 500 years bp. The trace element and isotopic diversity of AVF basalts require “small-scale” compositional heterogeneity in the underlying mantle that is comparable in volume to, or slightly larger than, the scale of individual eruptions in the AVF.Olivine from tephra and lava, representing the range of AVF compositions, was crushed and analysed for 3He/4He, and He and CO2 concentrations in an attempt to further characterize and explain the significance of the AVF “end-members”. AVF basalts show a negative covariation between the amount of CO2 released by crushing of olivine and the whole rock concentrations of highly incompatible trace elements, such as Ba, Rb, Nb, Zr, Ti and K. In contrast, the amount of He released by crushing shows no simple relations with the same incompatible elements or their ratios. This leads to a significant variation in CO2/3He ratios (9.4 × 107–3.5 × 109) that may relate to differences in magma ascent dynamics, as well as to different magma sources. The measured CO2/He ratios may have been influenced by varying amounts of CO2 diffusion into vapour bubbles within melt inclusions that depend on melt composition and magma ascent rate. However, petrographically there is no evidence for systematic differences in the size or quantity of vapour bubbles in olivine-hosted melt inclusions.3He/4He ratios in 14 AVF samples studied here show a narrow range from 6.57 to 7.26 RA (mean of 7.10 ± 0.26). This may imply a dominance of the mantle helium budget by small-scale heterogeneities. Alternatively, the 3He/4He results suggest that the tectonic and magmatic history of the mantle beneath the AVF has effectively hybridized the 3He/4He ratio to a larger extent than for highly incompatible trace element ratios and Pb-Nd-Sr isotopes. The value of ~7 RA for the mantle source of AVF basalts, in light of other evidence, suggests that there is a relatively homogeneous He isotope composition for the Zealandia-Antarctic mantle domain.

Thirty-eight lava and pyroclastic samples were collected from Mt. Erciyes and Mt. Hasan, the two largest stratovolcanic complexes of the Central Anatolian Volcanic Province in Turkey. More than 1000 zircon crystals were dated by Secondary Ion Mass Spectrometry (SIMS) applying U-Th disequilibrium and U-Pb methods. Model ages were calculated from zircon 230Th-238U-232Th isotopic compositions in combination with U-Th whole rock data of digested lava samples generated by Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS). Middle and Late Pleistocene ages dominate the dataset, but are complemented by both older (predominantly Early Pleistocene) and younger (Holocene) ages. U-Th disequilibrium and U-Pb zircon data provide maximum eruption ages that can be further specified by (U-Th)/He geochronology (zircon double dating). Additionally, these data are important to constrain the longevity and size of magmatic systems, and their potential for reactivation leading to potentially hazardous eruptions.

Small-scale basaltic magmatic systems are expressed as fields of monogenetic volcanoes at the Earth’s surface. Commonly but not exclusively magma compositions reflect processes at or near mantle source depths and crystal zoning patterns reveal rapid ascent rates. A significant question is that of how mantle sources yield very small volume magma batches over time scales of 10 6 - 10 7 years. The Auckland intraplate volcanic province of northern New Zealand consists of four small fields of monogenetic volcanoes. Each of these was active for a period of ~1 ma and the locus of activity migrated northward in discrete ~50 km steps during the last 3 ma. The most recent of these fields is the Auckland Volcanic Field (AVF) and it provides a key to understanding the source processes that yield monogenetic volcano fields. In the AVF individual eruptive events have produced compositionally distinct basalt magma within the range nephelinite to tholeiite. Eruptions have been irregularly spaced during the 200 kyr life of the field with repose periods of < 0.1 to 13 kyr. A significant flare-up in activity at about 30 kyr produced compositionally discrete events from spatially separate locations within a temporal interval of as little as 100 years. An interpretation of these data is that each of these events represents a discrete batch of magma extracted from a preexisting asthenospheric mantle cystal-liquid mush. We postulate that such a mush forms when upwelling mantle undergoes adiabatic partial melting and that it can exist as a metastable entity at the asthenosphere-lithosphere boundary for proponged periods (10 5 -10 6 years) during which time it can be tapped to create individual magma batches. The range of compositions observed in the AVF

U-series data are combined with major and trace element constraints to construct a detailed view of the magmatic system feeding the San Pedro-Linzor volcanic chain, aiding the understanding of how stratovolcanoes in extremely thick arc crust evolve. Lavas from the Quaternary San Pedro-Linzor volcanic chain (Central Andes) have (U-238/Th-230) ranging from 1.015 to 1.072, with U-238 excess even in the less evolved (similar to 57 wt% SiO2) analyzed lavas. Contrary to well-established trends between fluid mobile elements and U-238 excess, ((238)u/Th-230)(0) shows no systematic correlation with ratios indicative of fluid-driven melting (e.g. Ba/Hf and K/La). Moreover, the inverse correlation between (U-238/Th-232) with the amount of slab-derived fluid and the oxidation state of the mantle below Central Andes, which decreases eastwards, suggests that the main control of the U-238 excess is not associated with hydration of the mantle wedge. Changes in (U-238/Th-232) and (Th-230/Th-232)(0) are observed with variations in SiO2 and CaO + Al2O3 contents, and Sr-87/Sr-86 and Dy/Dy* ratios of the lavas. These changes correspond to increasing (U-238/Th-232) with decreasing Dy/Dy* and CaO + Al2O3 ratios, which is attributed to changes in crystallization of mineralogical phases within magmatic chambers during differentiation. Also, Th-230 in-growth is produced during stagnation within magmatic chambers located below the San Pedro-Linzor volcanic chain. Finally, a positive correlation between (Th-230/Th-232)(0) and Sr-87/Sr-86 indicates an important role of crustal contamination, and of new mafic inputs during evolution of the volcanic chain with time. Our observations suggest that better constraints of all magmatic processes are needed to fully understand the U-series disequilibria recognized for the different volcanic structures developed within subduction-related tectonic environments.