Volcanic Zone Research Articles

A 6.2 Ma‐Long Record of Major Explosive Eruptions From the NW Pacific Volcanic Arcs Based on the Offshore Tephra Sequences on the Northern Tip of the Emperor Seamount Chain

AbstractWe present a continuous ∼6.2 Ma long record of explosive activity from the Northwest Pacific volcanic arcs based on a composite tephra sequence derived from Ocean Drilling Program Sites 882A and 884B, and core MD01‐2416 on the Detroit Seamount. Geochemical fingerprinting of tephra glass using major and trace element analyses and correlations of tephra layers between the three cores allowed the identification of 119 unique tephras, suggesting eruptions of magnitude (M) of 5.8–7.8. Age estimates for all the identified eruptions were obtained with the help of published and further refined age models for the studied cores, direct 40Ar/39Ar dating of four ash layers, and Bayesian age modeling. The glass compositions vary from low‐ to high‐K2O basaltic andesite to rhyolite and exhibit typical subduction‐related affinity. The majority of the tephras originated from Kamchatka, only a few tephras—from the neighboring Kuril and Aleutian arcs. The glass compositions revealed no temporal trends but made it possible to identify their source volcanic zones in Kamchatka and, in some cases, to determine their source eruptive centers. Our data indicates episodes of explosive activity recorded in the Detroit tephra sequence at ∼6,200, 5,600–5,000, 4,300–3,700 ka, and almost continuous activity since ∼3,000 ka. Within the latter episode, the most active intervals can be identified at 1,700–1,600, 1,150–1,050, and 600–50 ka. Geochemically fingerprinted and dated Detroit tephra sequence form a framework for dating and correlating diverse paleoenvironmental archives across the Northwest Pacific and for studies of geochemical evolution of the adjacent volcanic arcs.

The Whakamaru magmatic system (Taupō Volcanic Zone, New Zealand), part 1: Evidence from tephra deposits for the eruption of multiple magma types through time

The Whakamaru group eruptions (349 ± 4 ka; Downs et al., 2014) are the largest known eruptions in the history of the young Taupō Volcanic Zone, Aotearoa New Zealand. The complex field relationships of the ignimbrites have thus far obscured the timing and history of their eruption(s). We present new evidence from fall deposits correlated with the Whakamaru eruptions to complement the ignimbrite record. Two coastal sections are characterized in detail. We group the tephra horizons into three packages: the older, smaller Tablelands and Paerata tephras; the overlying Kohioawa tephras (correlated with Whakamaru group eruptions); and the younger Murupara and Bonisch tephras. Major- and trace-element compositions suggest these tephras represent six distinct high-silica magma types, with the Kohioawa tephras representing three distinct magma compositions that are atypical of the TVZ. The distribution of Kohioawa magma types (types A, B, and C) changes through time, with the oldest deposits containing exclusively type A magma, the middle deposits containing types A and B, and the youngest deposits containing all three Kohioawa types. A combination of horizon-scale mineralogy and rhyolite-MELTS modeling suggests that only Kohioawa types B and C are saturated in sanidine – the presence of sanidine is atypical in Taupō Volcanic Zone magmas but has been previously documented in the Whakamaru group ignimbrites. Rhyolite-MELTS geobarometry reveals shallow storage pressures (∼50–150 MPa) for Kohioawa magmas. At least three different melt-dominated magma bodies sourced the Kohioawa tephras – these magma bodies were laterally juxtaposed and co-erupted for most of the Whakamaru eruptions. Magmas that preceded and post-dated the Whakamaru eruptions have more typical TVZ compositions, emphasizing the unique features of the Whakamaru system.

Comparison of Ground-Shaking Hazard for Segmented versus Multifault Earthquake-Rupture Models in Aotearoa New Zealand

Abstract Multifault ruptures are common for historical earthquakes, and here we consider their impact on seismic hazard. We compare ground-shaking hazard forecasts from the 2022 Aotearoa New Zealand National Seismic Hazard Model (NZ NSHM 2022), which incorporates many multifault ruptures (referred to as the multifault model) with modeled hazard from a simpler model of characteristic earthquakes on individual faults or fault segments (referred to as the segmented model). The multifault model includes very-low-probability rupture lengths of up to ∼1100 km and a mean of 221–234 km, whereas the segmented model primarily comprises rupture lengths of <200 km (mean, 43–51 km) and the maximum of 414 km. The annual rates of Mw 6.9–7.5 earthquakes are more than an order of magnitude higher for the segmented model (0.132–0.24/yr; recurrence times ∼4–7 yr) than the multifault model (0.027/yr; recurrence times 37 yr). Conversely, the rates of earthquakes are similar for segmented and multifault models at Mw>7.5 (0.018–0.031/yr; recurrence times 32–56 yr). Despite differences in rupture lengths and annual rates of earthquakes, the calculated ground-shaking hazard at 10% probability of exceedance (PoE) in 50 yr for the segmented model differs by <55% compared with the multifault model for 95% of sites across Aotearoa New Zealand. For 50% of sites, the modeled hazard differs by <20% between the two models. If a distributed seismicity model (DSM) is included in the hazard calculations, 95% of sites differ in modeled hazard by <18%, and 50% of sites differ by <2.2%. In most areas, seismic hazard at 10% PoE in 50 yr is greater for the segmented model than the multifault model, with notable exceptions along the central Alpine fault in the western South Island and the Taupō volcanic zone in the central North Island.

Two-stage evolution of a bimodal reservoir: The case of Holocene lavas of the Lanín composite volcano, Southern Volcanic Zone, Chile

Lanín is a composite volcano (∼39.38°S; 71.30°W) located in the Central Southern Volcanic Zone of the Andes. It is the southernmost member of the NW-SE volcanic alignment with the Villarrica and Quetrupillán composite volcanoes. During the Holocene, Lanín volcano erupted many lava flows, which we classify into three compositional groups: BAT (basalt, andesite, and basaltic trachyandesite), intermediate, and trachyte samples. The main recognised phenocrysts in the Lanín lavas are plagioclase, clinopyroxene, orthopyroxene, Fe–Ti oxides, and apatite. These mineral phases allow us to constrain the pre-eruptive (from the magma reservoir) conditions: temperature (985–1089 °C), pressure (1.8–4.1 kbar; equivalent to 6.5–15 km depth), and oxygen fugacity patch (∼QFM+0.4). In addition, textural features combined with pre-eruptive conditions suggest the existence of a crystal mush within the reservoir, which developed in two stages. The first stage considers the emplacement, crystal mush development, and eruption related to a melt of BAT composition. The residual melt evolved from BAT to trachytic primarily through fractional crystallisation. The second stage involves an evolved trachytic melt in the reservoir and the intrusion of a new, more mafic magma (presumably of BAT composition), which generates heating of the trachytic residual melt and crystal mush disaggregation. The fractional crystallisation also gives rise to scarce products of intermediate composition. This observation is consistent with the chemical constituents plots (TAS and Harker) and thermodynamic modelling.

Decoding subcontinental lithosphere processes: The key role of fractional crystallization in Central Andes monogenetic volcanism - Insight from El Negrillar volcanic field, Chile

Subduction zones are complex geodynamic settings in which volcanic arcs form due to the interaction between subducting slabs, water, and continental materials. Investigating this extensive Earth recycling system offers valuable insights into the exchange of materials between the crust and mantle. While previous research has primarily focused on analyzing polygenetic volcanoes to explore this interaction, monogenetic volcanic fields (MVF) present an opportunity to delve into the mechanisms operating within the upper and lower mantle. Monogenetic volcanoes are a class of volcanoes that are typically smaller in size but showcase a range of eruptive styles and compositions. These volcanoes can be found in various locations along the arc, including the main Central Volcanic Zone (CVZ) (arc-front volcanoes), and even far from the tectonic plate boundaries in the back-arc region (intraplate volcanism).We carried out a detailed geochemical study of El Negrillar (EN) MVF, located in the Central Andes main-arc, on the Altiplano-Puna Plateau's southwestern border. The volcanic field has 35 eruptive centers and a total of 86 eruptive phases originating from its three clusters: Northern, Central, and Southern. EN magmas range in composition from basaltic andesite to dacite and have produced over 6.8 km3 (DRE) of lava and pyroclastic material, which makes it the most voluminous volcanic field in the Central Andes, and therefore, an excellent example to study MVF in arc-systems. We have conducted an extensive study encompassing major and trace elements, as well as isotopic analysis using whole rock Sr-Nd-Pb. We also present an analysis of our results with available geochemical data from the back-arc and main-arc volcanoes, including other monogenetic volcanoes near EN (<80 km, EN's neighbors). The results revealed that EN magmas and their neighbors are strongly related and exhibit a clear similarity in major and trace element compositions and isotopic ratios, indicating a common source and origin of their melts. Our comparison across the arc surprisingly reveals similarities between EN and back-arc monogenetic volcanism. Both regions indicate geochemical signatures that do not support melting via slab metasomatism, typical of subduction zones. Instead, they show low Th/Ce (<0.1 ppm) and Ba/La (<30 ppm) and high Ce/Pb (>6 ppm), Ba/Th (>100 ppm), high 143Nd/144Nd > 0.51240, and La/Yb ratios at a given La/Sm compared to the main-arc polygenetic volcanoes. Interestingly, EN also exhibits adakite-like signatures with increasing SiO2 content (high Sr > 600 ppm, Sr/Y > 40, and high La/Yb > 20), a term used for igneous rock suites with chemical characteristics that are identical to those of adakites but produced through petrogenetic processes that do not include a slab component. We explore how fractional crystallization and crustal assimilation participate in the development of monogenetic volcanoes, and our findings underscore the significant influence of fractional crystallization on the monogenetic volcanic processes in the Salar de Atacama region. The geochemical changes observed in this area can be attributed to a combination of varying degrees of fractional crystallization within magmas generated through the partial melting of a garnet-enriched environment, which could be primary lower crust or partial melting of a peridotite mantle that has later equilibrated with garnet-bearing crustal melts.

Crustal Conditions Favoring Convective Downward Migration of Fractures in Deep Hydrothermal Systems

AbstractCooling magma plutons and intrusions are the heat sources for hydrothermal systems in volcanic settings. To explain system longevity and observed heat transfer at rates higher than those explained by pure conduction, the concept of fluid convection in fractures that deepen because of thermal rock contraction has been proposed as a heat‐source mechanism. While recent numerical studies have supported this half a century old hypothesis, understanding of the various regimes where convective downward migration of fractures can be an effective mechanism for heat transfer is lacking. Using a numerical model for fluid flow and fracture propagation in thermo‐poroelastic media, we investigate scenarios for which convective downward migration of fractures may occur. Our results support convective downward migration of fractures as a possible mechanism for development of hydrothermal systems, both for settings within active zones of volcanism and spreading and, under favorable conditions, in older crust away from such zones.

Pervasive Crustal Volcanic Mush in the Highly Stretched Sunda Plate Margin of Northern Sumatra

AbstractArc volcanism, crustal deformation, and their interplay are poorly understood in northwestern Sumatra. Traditional receiver function H‐κ stacking studies constrain the variations in crustal thickness and Vp/Vs ratio in volcanic zones but rarely estimate the melt fractions. Here, we propose a H‐Φ stacking method, a variant of the H‐κ stacking method, and apply it to the dense nodal array data from Aceh, northern Sumatra, to estimate crustal thickness, Vp/Vs ratio, and melt fraction. Most results show considerably high Vp/Vs ratios (∼1.98) and melt fractions (up to 19%), indicating pervasive crustal magmatic mush. The northwestern edge of the Aceh crust is much thinner (∼22 km) than extended crust globally, reflecting a highly stretched crust due to tectonic processes governing the opening of the Andaman Sea. This thin crust and high melt fractions explain the Bouguer gravity anomaly, and partly explain the northward migration of Quaternary volcanics.

Triassic felsic magmatism in SE Peninsular Malaysia: Petrogenesis and geodynamic implications for the Eastern Paleotethyan tectonic transition

Middle–Late Triassic volcanism and contemporary granitoids in East Malaya provide significant insights into the magmatic evolution and geodynamic processes of the Paleotethyan Ocean in SE Asia. This paper presents new zircon ages and whole-rock geochemical data including Sr-Nd-Pb-Hf isotopic analyses for newly identified felsic volcanic rocks and granites in SE Peninsular Malaysia. Zircon geochronological data constrain their formation time at 238–235 Ma. All samples have relatively high SiO2 contents with enrichment in light rare earth elements but have negative anomalies at Nb, Ta, Ti, and Eu on spidergrams. Calculated zircon saturation temperatures are between 840 °C and 957 °C. Samples have (87Sr/86Sr)i ratios between 0.70501 and 0.71014 and εNd (t) values ranging from −6.6 to −5.9, with (206Pb/204Pb)i = 18.45–18.77, (207Pb/204Pb)i = 15.68–15.71, and (208Pb/204Pb)i = 38.88–38.97. The zircon in-situ εHf (t) values and TDM2 ages range from −5.6 to +4.5 and 1.62 Ga to 0.98 Ga, respectively. The primary melting source which produced these felsic volcanic rocks and granites was Proterozoic crustal rocks with a juvenile middle-lower crustal component. Triassic volcanism in SE Peninsular Malaysia northerly correlates with synchronous volcanic rocks in the Lancangjiang and Chiang Khong-Lampang-Tak volcanic zones. Our data, along with regional observations, indicate that these volcanic rocks and granites formed in a localized extensional setting in response to the Paleotethyan slab breakoff. While the initial collision of Sibumasu with East Malaya may have occurred at ∼237 Ma.

New Zealand Fault-Rupture Depth Model v.1.0: A Provisional Estimate of the Maximum Depth of Seismic Rupture on New Zealand’s Active Faults

ABSTRACT We summarize estimates of the maximum rupture depth on New Zealand’s active faults (“New Zealand Fault-Rupture Depth Model v.1.0”), as used in the New Zealand Community Fault Model v1.0 and as a constraint for the latest revision of the New Zealand National Seismic Hazard Model (NZ NSHM 2022). Rupture depth estimates are based on a combination of two separate model approaches (using different methods and datasets). The first approach uses regional seismicity distribution from a relocated earthquake catalog to calculate the 90% seismicity cutoff depth (D90), representing the seismogenic depth limit. This is multiplied by an overshoot factor representing the dynamic propagation of rupture into the conditional stability zone, and accounting for the difference between regional seismicity depths and the frictional properties of a mature fault zone to arrive at a seismic estimate of the maximum rupture depth. The second approach uses surface heat flow and rock type to compute depths that correspond to the thermal limits of frictional instabilities on seismogenic faults. To arrive at a thermally-based maximum rupture depth, these thermal limits are also multiplied by an overshoot factor. Both the models have depth cutoffs at the Moho and/or subducting slabs. Results indicate the maximum rupture depths between 8 (Taupō volcanic zone) and &amp;gt;30 km (e.g., southwest North Island), strongly correlated with regional thermal gradients. The depths derived from the two methods show broad agreement for most of the North Island and some differences in the South Island. A combined model using weighting based on relative uncertainties is derived and validated using constraints from hypocenter and slip model depths from recent well-instrumented earthquakes. We discuss modifications to the maximum rupture depths estimated here that were undertaken for application within the NZ NSHM 2022. Our research demonstrates the utility of combining seismicity cutoff and thermal stability estimates to assess the down-dip dimensions of future earthquake ruptures.

Origin of the compositionally zoned Paso Puyehue Tephra, Antillanca Volcanic Complex, Chile

The origin of gaps or zoning in the composition of erupted products is critical to understanding how sub-volcanic reservoirs operate. We characterize the compositionally zoned magma that produced the 2053 ± 50 cal. yr BP Paso Puyehue Tephra from the Antillanca Volcanic Complex in the Andean Southern Volcanic Zone (SVZ). The 3.7 km3 Paso Puyehue Tephra is zoned from dacite (69 wt% SiO2) lapilli and ash comprising the lowermost 80% of the deposit that abruptly transitions upward into basaltic andesite scoria (54 wt% SiO2) making up the remaining ∼20%. Variations in whole-rock, matrix glass, and mineral compositions through the deposit allow us to estimate pre-eruptive magma storage conditions and to develop a model of how this magma body was generated.Our findings suggest that amphibole-bearing basaltic andesitic magma stored at ∼8.0 ± 1.3 km depth fractionally crystallized and cooled from 1048 ± 1.1 to 811 ± 28.6 °C under highly oxidizing conditions to produce silicic a melt that upon extraction and rise, pooled at ∼6.4 ± 1.2 km depth at temperatures as low as 810 °C before eruption. MELTS models suggest that crystallization of a basaltic andesite parent magma with 4 wt% dissolved H2O can produce the dacite under conditions predicted by mineral thermobarometers with phase compositions comparable to those measured in minerals. Pervasive normal zoning at the rims of plagioclase crystals—most pronounced at the transition between dacite and basaltic andesite, and compatible vs. incompatible trace element concentrations, suggest that magma mixing was limited and likely occurred at the interface between the dacitic and basaltic andesitic magmas during ascent within the conduit upon eruption. Compositionally bimodal tephras are increasingly recognized throughout the SVZ with several interpreted to reflect basaltic recharge and mixing into extant rhyolitic reservoirs. In further contrast to other SVZ rhyolitic products, e.g., from the nearby Cordón Callue and Mocho Choshuenco volcanoes, the Paso Puyehue magma was highly oxidized. This may reflect enhanced delivery of H2O from the subducting plate into the mantle wedge, which in turn may facilitate efficient extraction and separation of buoyant, low-viscosity rhyolitic melt from crystal-rich basaltic andesitic parent magmas and the co-eruption of both end members.

Decoding the state of stress and fluid pathways along the Andean Southern Volcanic Zone

Decoding means decrypting a hidden message. Here, the encrypted messages are the state of stress, fluid pathways, and volcano tectonic processes occurring in volcanoes of the Andean Southern Volcanic Zone (SVZ). To decode these messages, we use earthquake focal mechanisms, fault slip data, and a Monte Carlo simulation that predicts potential pathways for magmatic and hydrothermal fluids. From this analysis, we propose that SVZ volcanoes have three end-member stress patterns: (i) Stress-A, a strike-slip regime coupled with the regional far-field tectonic stress; (ii) Stress-B, an extensional regime that may be promoted by volcanic edifice loading and upward pressure due to magma inflation occurring within the upper brittle-crust; and (iii) Stress-C, a local and transient fluid-driven stress rotated ~90 degrees from Stress-A. Notoriously, Stress-C pattern was observed in most volcanoes with historical eruptions. We propose that volcanoes presenting Stress-B are attractive geothermal targets, while Stress-C could be used as a predicting signal for impending eruptions.

Seismicity and seismic monitoring of Canada’s volcanic zones

Canada’s recently active volcanic zones (e.g., eruptions during the past 10 000 years) are all located along the tectonic plate boundary region of western Canada, extending for more than 2000 km from southern British Columbia to the Yukon/Alaska border. In this article, we describe the history of seismic monitoring in and near these volcanic zones and the past and current seismicity detection thresholds. The most recently active volcanoes in Canada are Tseax Cone (∼1700s) and Lava Fork (∼1800s), both in northwestern British Columbia. However, no eruptions have occurred in Canada since the deployment of the earliest seismographs in 1898 (Victoria, BC) and 1904 (Sitka, Alaska). Seismic detection levels have decreased from M∼7 in 1900 to M∼0–1 (in many regions) today, with more than 120 seismic stations currently operating in British Columbia and the Yukon, including ∼20 seismic stations within the volcanic zones. The most recent significant seismic activity attributed to volcanic zones in Canada is the 2007 Nazko Cone earthquake swarm when nearly 1000 tiny (M &lt; 3) earthquakes occurred here over the span of about 2 months. These were all deep earthquakes (∼30 km) near the base of the crust and showed the patterns expected from an injection of magma deep into the crust. Prior to that, at the western end of the Anahim Volcanic Belt, more than 40 felt earthquakes occurred from 1940 to 1943. We provide a summary of these two swarms and other seismicity as well as some recent and ongoing studies into seismicity at some of Canada’s volcanic zones and new developments in seismic monitoring of volcanoes (including using distributed acoustic sensing).

Plio-Pleistocene rear-arc volcanism in the Southern Volcanic Zone: Eruptive styles of the Varvarco Volcanic Field

The Varvarco Volcanic Field (VVF) is located in the southern part of the Las Loicas Trough, as part of the Late Pliocene-Early Pleistocene rear-arc volcanic belt in the Transitional Southern Volcanic Zone (34.5–37°S). Its volcanic products show an elliptical distribution, elongated parallel to NW-SE main structures that regionally controlled the Las Loicas Trough. A detailed field and petrographic study was carried out to identify main lithofacies and establish its eruptive styles.The VVF magmatic evolution is initially characterized by a voluminous explosive stage represented in the area by dense and dilute pyroclastic density currents (PDC) deposits (massive lapilli tuffs, cross-stratified lapilli tuffs and diffuse-stratified tuffs). Afterwards, it evolved into an effusive stage represented by basaltic lava flows (coherent basalts), associated with Hawaiian to Strombolian eruptive style, which constitutes most of the VVF volume. The final stage of the VVF history was linked to a stratovolcano-type activity where both effusive (coherent basalts and andesites, and rhyolitic coulees) and explosive lithofacies (such as massive lithic breccias and massive lapilli tuffs) are described. Within this stage, the uppermost effusive levels were intruded by dacitic and rhyolitic domes and basaltic dykes. Available ages allow to conclude that the VVF emplacement was developed during Plio-Pleistocene times, linked to the re-steepening of the Nazca plate, after the Late Miocene Payenia shallow subduction regime.

The Eighth Wonder of the World in New Zealand: Seismic studies confirm the new Hochstetter paradigm

&lt;p&gt;The most famous tourist attractions in the southern hemisphere, in the nineteenth century were the Pink and White Terraces—New Zealand’s lost Eighth Wonder of the World. They were assumed lost in an1886 eruption. The unpublished 2018 data from passive seismic stations across the Lake Rotomahana overflow in the Taupō Volcanic Zone are examined for evidence of acoustic interfaces that may be traced to Te Tarata, the White Terraces, the stations were coincidentally placed over the reported course of the Kaiwaka Channel buried in the 1886 Tarawera eruption. There was no seismic evidence of the Channel at the reported altitude under either the Smith-Keam or Hochstetter paradigms. This absence is strong empirical negative evidence that the Kaiwaka Channel did not flow beneath today’s Lake Rotomahana overflow, as has been assumed since 1886 under the Smith-Keam paradigm. Unlike the seismic and GPR Black Terrace Crater and Te Tuhi’s Stream (aka Black Terrace Stream) bed evidence obtained by the same 2018 survey—there is no evidence of a pre-1886 eruption paleochannel beneath today’s overflow saddle at the lake and at the Kaiwaka altitude under the 1886 Smith-Keam paradigm or the contemporary Hochstetter paradigm, the latter based upon Hochstetter’s unique terrestrial survey of the Rotomahana Basin. The study reports strong empirical evidence contradicting the assumed Kaiwaka location and with it, the assumed locations of old Lake Rotomahana and the Pink and White Terraces. The Smith-Keam paradigm is thereby confounded. The seismic data provide concomitant empirical evidence for the Rotomahana altimetry and topography reported by Bunn and Nolden, who locate the Kaiwaka Channel 440 m west of the seismic stations. The Pink and White Terraces can no longer be assumed destroyed. They may yet be explored and recovered.&lt;/p&gt;

Effects of hydrogeochemistry on the microbial ecology of terrestrial hot springs.

Temperature, pH, and hydrochemistry of terrestrial hot springs play a critical role in shaping thermal microbial communities. However, the interactions of biotic and abiotic factors at this terrestrial-aquatic interface are still not well understood on a global scale, and the question of how underground events influence microbial communities remains open. To answer this, 11 new samples obtained from the El Tatio geothermal field were analyzed by 16S rRNA amplicon sequencing (V4 region), along with 191 samples from previous publications obtained from the Taupo Volcanic Zone, the Yellowstone Plateau Volcanic Field, and the Eastern Tibetan Plateau, with their temperature, pH, and major ion concentration. Microbial alpha diversity was lower in acid-sulfate waters, and no significant correlations were found with temperature. However, moderate correlations were observed between chemical parameters such as pH (mostly constrained to temperatures below 70°C), SO4 2- and abundances of members of the phyla Armatimonadota, Deinococcota, Chloroflexota, Campilobacterota, and Thermoplasmatota. pH and SO4 2- gradients were explained by phase separation of sulfur-rich hydrothermal fluids and oxidation of reduced sulfur in the steam phase, which were identified as key processes shaping these communities. Ordination and permutational analysis of variance showed that temperature, pH, and major element hydrochemistry explain only 24% of the microbial community structure. Therefore, most of the variance remained unexplained, suggesting that other environmental or biotic factors are also involved and highlighting the environmental complexity of the ecosystem and its great potential to test niche theory ecological associated questions. IMPORTANCE This is the first approach to investigate whether geothermal processes could have an influence on the ecology of thermal microbial communities on a global scale. In addition to temperature and pH, microbial communities are structured by sulfate concentrations, which depends on the tectono-magmatic settings (such as the depth of magmatic chambers) and the local settings (such as the availability of a confining layer separating NaCl waters from steam after phase separation) and the possibility of mixing with more diluted fluids. Comparison of microbial communities from different geothermal areas by homogeneous sequence processing showed that no significant geographic distance decay was detected on the microbial communities according to Bray-Curtis, Jaccard, unweighted, and weighted Unifrac similarity/dissimilarity indices. Instead, an ancient potential divergence in the same taxonomic groups is suggested between globally distant thermal zones.

Petrological and geochemical constraints on the magmatic evolution at the Ampato-Sabancaya compound volcano (Peru)

In order to gain insights into continental arc magmatic processes, we have conducted a petrological and geochemical study of major and trace elements and Sr, Nd, and Pb isotopes of the Ampato-Sabancaya compound volcano, which belongs to the Andean Central Volcanic Zone (CVZ). Whole-rock compositions for Ampato and Sabancaya range from andesites to dacites (56.7–69.3 wt% SiO2) and both belong to a medium- to high-K calk-alkaline magmatic series. Ampato-Sabancaya samples are characterized by high contents of large-ion lithophile elements (LILE; e.g., K, Rb, Ba, Th), low concentrations of high field strength elements (HFSE; e.g., Nb, Zr) and heavy rare earth elements (HREE; e.g., Yb), with consequently high La/Yb and Sr/Y ratios. An increase in these ratios is usually interpreted as a result of magmatic differentiation in the presence of garnet in the deep crust. A detailed analysis reveals that the rocks of Ampato-Sabancaya display three different compositional groups. (1) The first, composed mainly of andesites (56.7–59.8 wt% SiO2), corresponds to lavas from the early stage of the Ampato Basal edifice, as well as pyroclastic deposits from the Ampato Upper edifice. (2) The second group corresponds to andesitic and dacitic compositions (60.0–67.3 wt% SiO2) from the Ampato Basal edifice (Moldepampa stage), the Ampato Upper edifice, and the Sabancaya edifice. (3) The third group corresponds to dacitic compositions (65.0–69.3 wt% SiO2) associated with the Corinta Plinian fallout and pyroclastic flow deposits from the Ampato Upper edifice. This last group of dacites, erupted during the Ampato Upper edifice stage, have drastically different compositions from the other groups with Sr/Y (<27) and Sm/Yb (<4.7) ratios lower than other lavas and lacking evidence of amphibole and/or garnet fractionation during their genesis. As a whole, Sr, Nd, Pd isotopic ratios suggest that mantle-derived magmas are significantly affected by assimilation processes during their evolution, due to the thick (65–70 km) continental crust beneath the CVZ in southern Peru. In summary, the magmatic evolution of group 1 and 2 can be explained by a two-step model in which primitive magmas evolved in the deep crust in the so-called melting-assimilation-storage-homogenization (MASH)-type reservoirs by assimilation-fractional crystallization (AFC) processes involving garnet and/or amphibole. Then, amphibole-dominated upper crustal AFC processes and magma mixing are responsible for the geochemical diversity of the main ASCV trend. In contrats, the group 3 dacites followed an upper crustal AFC process (without amphibole) from a different primitive magma, which did not suffer the high pressure, garnet-dominated AFC processes. This evolution highlights the complexities associated to magma genesis and differentiation at continental arcs contructed on a thick crust.

Improving tephrostratigraphy and cryptotephrostratigraphy since 1 Ma of Hole U1437B in the Izu-Bonin arc, NW Pacific: Differentiation of widespread tephras with similar shard chemistries

We investigated the deep-sea sedimentary sequence of Hole U1437B, corresponding to the last 1 Ma, in the Izu-Bonin arc, NW Pacific Ocean, and refined its tephrostratigraphy. We correlated many tephras and cryptotephras with terrestrial and marine tephras on the basis of the major- and trace-element compositions of their glass shards by referring to the reported tephrostratigraphy of marine sediments in core MD012422 (since 0.35 Ma) off Shikoku Island, in Holes ODP1151C (0.2–0.8 Ma) and C9001C (since ca. 0.8 Ma) off northern and northernmost Honshu, respectively, and on the Boso Peninsula (since 1 Ma). Many widespread tephras and cryptotephras were detected in the hole such as those originated from the Kyushu volcanic zone (from north to south, Yufu-Tsurumi, Shishimuta, Aso, Kakuto, Kobayashi, Aira, Ata, and Kikai volcanoes/calderas), Hakkoda-Kokumoto tephra originated from Hakkoda caldera, northernmost Honshu, and some tephras probably originated from source(s) in northern Honshu. Among the widespread tephras, those with similar shard chemistries occurred at different horizons. Kasamori 5 tephra (Ks5) was newly detected by this study in a position above the previously reported "Ks5" horizon in Hole U1437B. The newly detected Ks5 tephra occurs in the marine isotopic stage (MIS) 12 segment of the δ18O stratigraphy, consistent with the reported stratigraphic age of Ks5 (MIS 12b–c) in Hole C9001C. Although the reported "Ks5" horizon also occurs in the MIS 12 segment in Hole U1437B, it is actually a different unidentified tephra, as indicated by its slightly different shard chemistry. Further, we correlated Kasamori 10 tephra (Ks10: mid-MIS 13) in Hole U1437B to subspike G19.3 in Hole C9001C but not to subspike G4.4 in Hole ODP1151C. Although subspike G4.4 in Hole ODP1151C was previously estimated on the basis of its shard major-element composition to correspond to subspike G19.3 in Hole C9001C, their shard trace-element compositions differ. Instead, on the basis of their shard chemistries, we correlated subspike G4.4 in Hole ODP1151C to spike G90 in Hole U1437B (MIS 14), which occurs below the Ks10. This tephra has not been reported in the marine Kasamori Formation on the Boso Peninsula. Further, spike G7 in Hole ODP1151C, which is below subspike G4.4 and above spike G9 (a correlative of Ks22 and Kaisho-Kamitakara tephra, MIS 16), is here correlated to Ks18 in the MIS 15 horizon of Hole U1437B on the basis of their shard chemistries. The stratigraphic ages of Ks5, Ks10, the spike G90 tephra, and Ks18 at most (but not all) locations are roughly consistent with the age of a globally correlated biohorizon, the last appearance datum of Pseudoemiliania lacunosa (ca. 0.45 Ma). These findings emphasize that Hole U1437B sediments are as good as or better than the marine sediments on the Boso Peninsula as archives of the regional tephrostratigraphy. Thus, they are useful for improving the Middle Pleistocene tephrostratigraphy in the NW Pacific region.

Insights into the explosive eruption history of the Campanian volcanoes prior to the Campanian Ignimbrite eruption

The Campanian Volcanic Zone (CVZ) comprises multiple active volcanoes and includes the highly productive Campi Flegrei and Ischia caldera systems. These caldera volcanoes have produced probably the largest eruptions in Europe in the past 200 ka, such as the Monte Epomeo Green Tuff (MEGT; Ischia) at ca. 56 ka and the Campanian Ignimbrite (CI; Campi Flegrei) at ca. 40 ka, which form widespread isochrons across the Mediterranean region. These closely-spaced volcanic centres erupt phonolitic to trachytic glass compositions that are similar, and thus it can be challenging to correlate tephra deposits to specific volcanic sources. Here we present a detailed tephrostratigraphy for pre-CI eruption activity using the units preserved within a sequence at the coastal Acquamorta outcrop, on the western side of the CI caldera rim. Both the MEGT and CI units are present in the section, and they bracket twelve eruption units that were logged and sampled. New major and trace element glass chemistry data have been acquired for these Acquamorta tephra deposits. Three eruption deposits from Ischia and nine from Campi Flegrei are identified, which helps constrain the tempo of volcanic activity of these centres between the large caldera-forming eruptions. The three Ischia tephra deposits between the MEGT and the CI are indistinguishable based on both major and trace element glass chemistry and cannot be correlated to a specific or known eruption in this interval, such as the Schiappone tephra. The compositional variations between the Campi Flegrei eruptions reveal temporal shifts in the composition of the tephra deposits that reflect changes in the magmatic system prior to the CI eruption. These deposits indicate that there were at least nine eruptions at Campi Flegrei within 16 ka of the enormous CI eruption, and suggest that there was no significant period of repose before the caldera generating eruption.

BOOM! Tephrochronological dataset and exploration tool of the Southern (33–46° S) and Austral (49–55° S) volcanic zones of the Andes

Tephrochronology studies the deposits of explosive volcanic eruptions in the stratigraphic record. The Southern (SVZ, 33–46° S) and Austral (AVZ, 49–55° S) Volcanic Zones of the Andes are two very active volcanic zones where tephrochronology is of great use. There, it can be used to improve chronologies of paleoenvironmental records in Patagonia, an area providing valuable records at global scale; as well as to identify areas likely to be affected by volcanic eruptions in the future, essential for producing volcanic hazard maps. The close proximity of many volcanic centers with recurrent explosive activity, which have very similar geochemical compositions, and very often poor age constraints, represent a challenge for the study of tephrochronology in the region. In addition to this, the ever-growing amount of tephrochronological information in the area, dispersed in different types of publications which vary greatly in format, makes the integration of the data produced by different actors, and consecutively its interpretation, increasingly difficult. Here we address this issue by compiling the BOOM! dataset, which integrates ∼30 years of research on 32 active volcanic centers and 132 different eruptions, which took place during the last 20,000 years. To help users find and reuse data in the large dataset, we developed an online platform which provides user-friendly tools for exploring it, and helps users download subsets of it. To integrate this very heterogeneous information, special attention was given to include information which allows users to evaluate data quality and comparability, as well as to provide tools in the explorer for users to filter data by different criteria. The integration of this dataset opens new perspectives for the development of novel visualizations of tephrochronological data, for example, to better understand the multidimensional uncertainties associated with it. For example, uncertainties associated with analytical precision, with age estimates of both tephra deposits and volcanic eruptions, and of tephra classification. Additionally, it allows for the use of robust statistical tools to correlate tephra deposits, including those based on machine learning algorithms, which are here explored.

Digital Tools for the Promotion of Geological and Mining Heritage: Case Study from the Thames Goldfield, Aotearoa, New Zealand

The geoheritage value in the Thames District, North Island, New Zealand, is notable for its over 50 epithermal gold deposits associated with the Coromandel Volcanic Zone, significant to the region’s geological, cultural, and mining heritage. This case study was conducted in collaboration with the Thames School of Mines and Mineralogical Museum to develop a series of web-based applications for public outreach and an accessible museum experience through the utilization of specimens from the mineralogical museum. This research applies a conceptual framework of ex situ geoheritage to explore links between local geology with cultural and mining heritage. Minerals and rock specimens collected for the Thames School of Mines Mineralogical Museum were used to create 3D virtual models demonstrating the epithermal mineralization in the Thames Goldfield. Outputs of this project consist of two digital products, including a digital mineral and rock repository and the dissemination of the geological collection through integrating the photogrammetric models into a user-friendly outreach, ArcGIS Storymaps, to depict the geoheritage relationship of the specimens to regional gold mining, and at the same time, to be developed to be implemented in geoscience education and communication. The results of this paper are intended to promote the use of digital tools for enhancing and raising awareness of the geoheritage values of the Thames Goldfield. This approach has relevance for Papua New Guinea and the Pacific Islands in raising awareness of geological, mineral, and mining heritage within widely distributed and often isolated communities across island archipelago nations.