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Shoshonitic rocks represent the transition between calcalkaline and alkaline rocks, often formed during the last stages of uplift in zones of continental collision. This study describes the characterization of Kyrdem granitoids of Shillong plateau, Meghalaya, North East India, as felsic shoshonites. The study also documents petrogenesis of the shoshonites and suggests significant magma mixing and crust–mantle melt interaction as prime mechanisms for parental magma evolution. Crustal melt has most probably been sourced from a metabasaltic middle crust, while the mantle source is represented by an enriched sub-continental lithospheric mantle, metasomatized by sediment melt, during an earlier subduction event. [ABSTRACT FROM AUTHOR]

Kirishima volcano consists of more than 20 eruptive centers. Among them, Shinmoe-dake had magmatic eruptions in October 2017 and March 2018. Subsequently, another active cone, Iwo-yama, had phreatic eruptions in April 2018. These events were unique in that the 2018 eruption was the first effusion-dominated eruption of Shinmoe-dake and the first simultaneous activity of two cones of the Kirishima volcanic group ever documented. We report the detailed sequence of the events by combining areal photos, satellite images, and seismo-acoustic data analyses with the other published information. The seismo-acoustic data clarify the eruption onset and the transitions of the behaviors in three stages for each of the 2017 and 2018 eruptions. For both eruptions, we present regularly repeated tremors or 'drumbeat' earthquakes in the second stage, which interpret as gas separation from magma, leading to the ash-poor plume in the 2017 eruption or the effusive eruption in the 2018 event. We also propose that the 2017 and 2018 eruptions of Shinmoe-dake and the 2018 eruption of Iwo-yama are sequential events linked by the degassing of magma beneath Shinmoe-dake. An eruption like the 2017–2018 eruptions of Shinmoe-dake would leave few geological records and could be captured only by modern techniques. Although Shinmoe-dake has been believed to be an example of less-frequent eruptions, effusive eruptions like the 2018 case might have occurred more frequently in the past , but the following eruptions had obscured their records. The timelines summarized in this study will be useful in future studies of Kirishima volcanoes and world equivalences. [ABSTRACT FROM AUTHOR]

We infer the temporal changes in the pressure sources that induced crustal deformation during the 2018 Shinmoe-dake eruption using strain and tilt observations and discern that the deep magmatic activity associated with the early stage of this eruption began approximately 19 h earlier than the previously defined onset of magmatic activity. Distinct tilt changes were observed from around 09:00 on 6 March to 12:00 on 8 March 2018 (JST), coincident with observed lava outflow into the crater and lava dome formation. Existing studies have attributed this tilt change to the onset of the deflation of a spherical pressure source located at ~ 7 km bsl (below sea level) to the northwest of Shinmoe-dake. Here we examine strain and tilt data that were acquired in the Kirishima volcanic group, and we find that the distinct changes in the measured strain at Isa-Yoshimatsu Observatory began at around 14:00 on 5 March. This change can be explained by the deflation of a spherical pressure source, thereby suggesting that the onset of magma ascent was earlier than previously thought. The time variation in the spherical pressure source is estimated using the time-dependent inversion of the Ensemble Kalman Filter; the deflation source ascended from ~ 11 to 7 km bsl during Phase 1 (14:00 on 5 March to 06:00 on 6 March) and descended from 7 to 8 km bsl during Phase 2 (06:00 on 6 March to 12:00 on 8 March). Interferometric synthetic aperture radar analysis suggests that a dike intrusion had occurred just below Shinmoe-dake crater until 5 March, and this inflatable crustal deformation is attributed to the emplacement of residual volcanic fluids from the 2011 eruption. It is also known that the surface eruptive activity increased during Phase 1, including an increase in ash venting from the night of 5 March. These strain and tilt observations, therefore, suggest that magma ascended from ~ 11 km bsl to the magma reservoir at 7 km bsl during Phase 1, followed by a deflation of the magma reservoir during Phase 2 due to the large magma supply to the surface. [ABSTRACT FROM AUTHOR]

We obtain new images of the 3D resistivity structure of the Wudalianchi volcanic field (WVF). No low‐resistivity structure is found beneath Laoheishan and Huoshaoshan volcanoes in the WVF, which challenges the hypothesis of one or more magma reservoirs in the upper crust of this region. We observe a low‐resistivity body beneath Weishan volcano; however, estimated magma emplacement rates conflict with the observed volume of that body. Due to the relatively low geothermal gradient and surface heat flow in the area, magma would cool rapidly and could not be sustained for a long time unless new magma was regularly introduced into the system, but our observations do not support this scenario. We suggest that the magma in the WVF mainly originates from the mantle or the base of the crust with little crustal residence, and that the low‐resistivity body in the upper crust is likely due to saline aqueous free fluids. Plain Language Summary: The origin of magma, whether it is derived directly from the deep mantle or has previously resided in the crust, plays a crucial role in determining volcanic eruption mechanisms. The presence of a magma reservoir in the shallow crust often signifies an increased risk of volcanic eruptions. The Wudalianchi volcanic field (WVF) is situated in northeastern China. Earlier research suggested the existence of a magma reservoir beneath the Weishan volcano within the WVF. However, our study reveals an absence of magma reservoirs beneath the more recently erupted Laoheishan and Huoshaoshan volcanoes. This raises the question of why a magma reservoir is present beneath Weishan, which experienced an eruption 0.5 Ma ago, rather than beneath Laoheshan and Huoshaoshan, which erupted a mere 300 years ago. Furthermore, the WVF is characterized by an extremely low geothermal gradient, causing magma in the shallow crust to lose substantial heat and cool rapidly, unless replenished by a continuous influx of high‐temperature magma. Nevertheless, the volume of magma injection inferred from the low‐resistivity body beneath Weishan is inconsistent with numerical simulation results. Consequently, we suggest that the low‐resistivity body beneath Weishan volcano is instead a structure containing saline aqueous free fluids, not magma. Key Points: Electrical structure of the Wudalianchi volcanic field (WVF) is imagedSubsurface beneath Laoheishan and Huoshaoshan volcanoes is highly resistiveLow‐resistivity body beneath Weishan volcano is due to saline aqueous free fluids [ABSTRACT FROM AUTHOR]

The emplacement of shallow magma chambers within a carbonate basement is a typical feature of many volcanic systems around the world. The accompanying formation of exoskarns, endoskarns, cumulates, exsolved fluids and differentiated melts at the interface between the magma chamber and carbonate host-rock is well documented through mineralogical and geochemical studies of ejected skarns and cumulates and through fluid and melt inclusion studies. This review presents the current knowledge on the interaction of alkaline magma chambers with carbonate-bearing host-rocks, with a focus on the geochemical evolution and mineralization at the outer margins of the magma chamber and the accessory mineral phases at Somma-Vesuvius, Colli Albani and Merapi volcanic systems. Furthermore, we discuss how this interaction and its products, especially the CO2 released during the thermometamorphic decarbonation of the carbonate host-rock, impacts the eruptive behavior in all three systems. [ABSTRACT FROM AUTHOR]

The research on highly fractionated granite has significant implications for both the evolution and compositional maturation of the continental crust and metallogenic exploration. As a means of further understanding crustal evolution and promoting ore exploration in the Bangong–Nujiang metallogenic belt (BNMB), we present the petrography, zircon LA–ICP–MS U–Pb age, and Hf isotopic data, along with the whole-rock geochemical and Sr–Nd isotopic composition on Kese highly fractionated granite in the Baingoin area within the BNMB, central Tibet. The results show that Kese granite possesses a zircon U–Pb age of 127.8 ± 1.7 Ma and a relative enrichment in zircon Hf isotopic composition (−12.8~+0.3) with a two-stage Hf model age of 1.2~2.0 Ga. This granite belongs to the high-K calc-alkaline series, characterized by a strongly peraluminous feature, and is enriched in large-ion lithophile elements (LILEs) and Nd isotopes (−7.86~−7.74). The granite was likely to have been derived from the mixed melts derived from 40%~45% juvenile basaltic lower crust, 15%~20% ancient lower, and 40% middle–upper, following intense fractional crystallization processes involving amphibole, biotite, plagioclase, and some accessory minerals during the magma's evolution. We infer that Kese highly fractionated granite can be formed from the continental collision of the Lhasa–Qiangtang terranes initiated before 128 Ma. The reworking of pre-existing juvenile and ancient crustal materials drove the composition of the northern Lhasa terrane to that of a mature continental crust. Moreover, the distinctive geochemical features have shown that the high degree of differentiation led to intense magmatic–hydrothermal interaction during the formation of Kese granite. A comparison of the geochemical characteristics of mineralized and barren granites suggests that the highly fractionated granites in Baingoin from the BNMB have a high economic potential and are suitable for preliminary exploration of Sn–W-(U) deposits. [ABSTRACT FROM AUTHOR]

Fluorine-rich granites and rhyolites occur throughout the southern Rocky Mountains, but the origin of F-enrichment has remained unclear. We test if F-enrichment could be inherited from ancient mafic lower crust by: (1) measuring amphibole compositions, including F and Cl contents, of lower crustal mafic granulite xenoliths from northern Colorado to determine if they are unusually enriched in halogens; (2) analyzing whole-rock elemental and Sr, Nd, and Pb isotopic compositions for upper crustal Cretaceous to Oligocene igneous rocks in Colorado to evaluate their sources; and (3) comparing batch melting models of mafic lower crustal source rocks to melt F and Cl abundances derived from biotite data from the F-rich silicic Never Summer batholith. This approach allows us to better determine if the mafic lower crust was pre-enriched in F, if it is concentrated enough to generate F-rich anatectic melts, and if geochemical data support an ancient lower crustal origin for the F-rich rocks in the southern Rocky Mountains. Electron microprobe analyses of amphibole in lower crustal mafic granulite xenoliths show they contain 0.56–1.38 wt% F and 0.45–0.73 wt% Cl. Titanium in calcium amphibole thermometry indicates that the amphiboles equilibrated at high to ultrahigh temperature conditions (805 to 940 °C), and semiquantitative amphibole thermobarometry indicates the amphiboles equilibrated at 0.5 to 1.0 GPa prior to entrainment in magmas during the Devonian. Mass balance calculations, based on these new measurements, indicate parts of the mafic lower crust in Colorado are at least 3.5 times more enriched in F than average mafic lower crust. Intrusions coeval with the Laramide Orogeny (75 to 38 Ma) pre-date F-rich magmatism in Colorado and have Sr and Nd isotopic compositions consistent with mafic lower crust ± mantle sources, but many of these intrusions contain elevated Sr/Y ratios (>40) that suggest amphibole was a stable phase during magma generation. The F-rich igneous rocks from the Never Summer igneous complex and Colorado Mineral Belt also have Sr and Nd isotopic compositions that overlap with the lower crustal mafic granulite xenoliths, but they have lower Sr/Y, higher Nb and Y abundances, and distinctly less radiogenic 206Pb/204Pbi compositions than preceding Laramide magmatism. Batch melt modeling indicates low-degree partial melts derived from rocks similar to the mafic lower crustal xenoliths we analyzed can yield silicic melts with >2000 ppm F, similar to estimated F melt concentrations for silicic melts that are interpreted to be parental to evolved leucogranites. We suggest that F-rich silicic melts in the southern Rocky Mountains were sourced from garnet-free mafic lower crust, and that fluid-absent breakdown of amphibole in ultrahigh temperature metamorphic rocks was a key process in their generation. Based on the composition of high-F amphibole measured from lower crustal xenoliths, the temperature of amphibole breakdown and melt generation for these F-enriched source rocks is likely >100 °C higher than similar lower crust with low or average F abundances. As such, these source rocks only melted during periods of unusually high heat flow into the lower crust, such as during an influx of mantle-derived magmas related to rifting or the post-Laramide ignimbrite flare-up in the region. These data have direct implications for the genesis of porphyry Mo mineralization, because they indicate that pre-enrichment of F in the deep crust could be a necessary condition for later anatexis and generation of F-rich magmas. [ABSTRACT FROM AUTHOR]

Subduction of the Paleo-Pacific Plate plays a key role in the Early Jurassic magmatism evolution in the Yanbian area, Northeast China. In this paper, zircon U–Pb ages, whole-rock geochemical, and Sr–Nd–Hf isotopic compositions are presented. The Early Jurassic gabbros, diorite enclaves, granodiorites, and granites ages range from 183 to 189 Ma. They are characterized by enrichment in large-ion lithophile elements and depletion in high-field strength elements. The gabbros are classified as low- and medium-K tholeiitic, granodiorites and granites are high-K calc-alkaline I-type, and diorite enclaves are calc-alkaline transitional series. The gabbros have zircon εHf(t) values of 6.81–9.89, whole-rock 87Sr/86Sr(i) = 0.7043–0.7044, and εNd(t) from 2.72 to 2.80. The diorite enclaves have zircons with εHf(t) values of 8.26–12.80, whole-rock 87Sr/86Sr(i) = 0.7051, and εNd(t) from 0.96 to 1.09. The granodiorites and granites have zircon εHf(t) values of 7.59–12.87, whole-rock 87Sr/86Sr(i) = 0.7042–0.7066, and εNd(t) from 2.33 to 2.61. These data indicate that gabbroic magmas were derived from partial melting of a depleted mantle wedge metasomatized by subduction-related fluids. The basaltic magma underplated and heated the juvenile crust, whereas the granodiorites and granites might be the product of fractional crystallization of a mixture of basaltic and felsic magmas or derived from partial melting of the juvenile lower crust. Our data constrain the petrogenesis of these Early Jurassic intrusive rocks which are attributed to subduction of the Paleo-Pacific Plate beneath Eurasia continent in northeastern China. [ABSTRACT FROM AUTHOR]

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Plagioclase microlites in a magma nucleate and grow in response to melt supersaturation (Δϕplag). The resultant frozen plagioclase crystal size distribution (CSD) preserves the history of decompression pathways (dP/dt). SNGPlag is a numerical model that calculates the equilibrium composition of a decompressing magma and nucleates and grows plagioclase in response to an imposed Δϕplag. Here, we test a new version of SNGPlag calibrated for use with basaltic andesite magmas and model dP/dt for the ca. 12.6 ka Curacautín eruption of Llaima volcano, Chile. Instantaneous nucleation (Nplag) and growth (Gplag) rates of plagioclase were computed using the experimental results of Shea and Hammer (J Volcanol Geotherm Res 260:127–145, 10.1016/j.jvolgeores.2013.04.018, 2013) and used for SNGPlag modeling of basaltic andesite composition. Maximum Nplag of 6.1 × 105 cm h−1 is achieved at a Δϕplag of 44% and the maximum Gplag of 27.4 μm h−1 is achieved at a Δϕplag of 29%. Our modeled log dP/dtavg range from 2.69 ± 0.09 to 6.89 ± 0.96 MPa h−1 (1σ) with an average duration of decompression from 0.87 ± 0.25 to 16.13 ± 0.29 h assuming a starting pressure Pi of 110–150 MPa. These rates are similar to those derived from mafic decompression experiments for other explosive eruptions. Using assumptions for lithostatic pressure gradients (dP/dz), we calculate ascent rates of < 1–6 m s−1. We conducted a second set of Monte Carlo simulations using Pi of 15–30 MPa to investigate the influence of shallower decompression, resulting in log dP/dtavg from 2.86 ± 0.49 to 6.00 ± 0.86 MPa h−1. The dP/dt modeled here is two orders of magnitude lower than those calculated by Valdivia et al. (Bull Volcanol, 10.1007/s00445-021-01514-8, 2022) for the same eruption using a bubble number density meter, and suggests homogeneous nucleation raises dP/dt by orders of magnitude in the shallow conduit. Our modeling further supports the rapid-ascent hypothesis for driving highly explosive mafic eruptions. [ABSTRACT FROM AUTHOR]

Despite the first-order importance of crystallisation–differentiation for arc magma evolution, several other processes contribute to their compositional diversity. Among them is the remelting of partly crystallised magmas, also known as cumulate melting or 'petrological cannibalism'. The impact of this process on the plutonic record is poorly constrained. We investigate a nepheline-normative dyke suite close to the Blumone gabbros, a large amphibole-gabbro unit of the Tertiary Southern Alpine Adamello igneous complex. The compositions of the studied dykes are characterised by low SiO2 (43–46 wt. %), MgO (5.0–7.2 wt. %), Ni (18–40 μg/g), and high Al2O3 (20.2–22.0 wt. %) contents. Phenocrystic plagioclase in these dykes exhibits major, trace, and Sr isotope compositions similar to Blumone cumulate plagioclase, suggesting a genetic link between the nepheline-normative dykes and the amphibole-gabbro cumulates. We tested this hypothesis by performing saturation experiments on a nepheline-normative dyke composition in an externally heated pressure vessel at 200 MPa between 975 and 1100 °C at fO2 conditions close to the Ni–NiO buffer. Plagioclase and spinel are near-liquidus phases at and above 1050 °C, contrasting with the typical near-liquidus olivine ± spinel assemblage in hydrous calc-alkaline basalts. The alkaline nature of the dykes results from the abundance of amphibole in the protolith, consistent with melting of amphibole-gabbro cumulates. We modelled the heat budget from the repeated injection of basaltic andesite into a partly crystallised amphibole-gabbro cumulate. The results of this model show that no more than 7% of the cumulate pile reaches temperatures high enough to produce nepheline-normative melts. We propose that such nepheline-normative dykes are a hallmark of hydrous cumulate melting in subvolcanic plumbing systems. Therefore, ne-normative dykes in arc batholiths may indicate periods with high magma fluxes. [ABSTRACT FROM AUTHOR]

Texture and particularly compositional variations of zoned minerals are important to understand trans-crustal magma plumbing systems of volcanoes. The Sipisupisu volcano in Sunda arc, northern Sumatra, occurs as a stratocone on the northwestern tip of the Toba Caldera and belongs to the large Toba volcanic system, which has produced two super-eruptions in the Quaternary. Compositionally zoned olivine, plagioclase and clinopyroxene grains, together with orthopyroxene reaction rims around olivine from basalts and basaltic andesites of the Sipisupisu volcano indicate open-system processes characterized by multiple episodes of magma recharge and mixing. Based on compositional variations of a variety of zoned olivine and clinopyroxene crystals, melts ascended from the large basaltic magma reservoir at the Moho have resided in at least three staging magma reservoirs within the crust. One magma reservoir is Si-saturated and located < 13 km deep in the upper crust, underlain by two Si-undersaturated ones at a depth from ~ 13 to 25 km. Fe–Mg diffusion modeling shows that olivine residence time from mixing of compositionally more evolved magmas to eruption varies from ~ 7 days to 9 months, whereas that from recharge of more primitive magmas to eruption is ~ 6 months to 5 years. This timescale is, on average, longer than olivine residence time of the majority of mafic arc volcanoes worldwide and may favor prolonged crystal fractionation. The multiple staging magma reservoirs and prolonged crystal residence time of the Sipisupisu volcano could potentially be linked to the large basaltic magma reservoir at depth. Finally, mixing of Si-saturated and Si-undersaturated magmas probably triggered Sipisupisu eruption. [ABSTRACT FROM AUTHOR]

The flux of eruptible magma into a magmatic plumbing system influences eruption size and timing. If magma transfer is possible between two hydraulically‐connected magma lenses, system destabilization can tap a larger magma volume than stored in any one melt lens. This study identifies two distinct magma reservoirs beneath Ambrym, a basaltic island volcano in Vanuatu, during the time period February 2019 to January 2022. Using InSAR time series and a data assimilation approach, we estimate pressure changes within two reservoirs (located 5–7 and 4–6 km b.s.l.). Furthermore, a theoretical model demonstrates that the reservoirs may not currently be hydraulically connected, despite evidence of physical mixing of magma derived from each reservoir during the December 2018 eruption. These findings further our understanding of how magmatic plumbing systems at basaltic calderas may change after rift‐zone eruptions. Plain Language Summary: To improve eruption forecasting, it is important to put limits of the volume of eruptible magma stored beneath a volcano. There is evidence that regions of magma storage can be approximated by multiple "reservoirs" of magma beneath a single volcano. If magma can be transferred between these reservoirs, more magma may be available when an eruption occurs. We use models of ground displacements measured by satellite over 3 years to identify two reservoirs of magma at Ambrym volcano, located in Vanuatu, from 2019 to 2022. We then estimate how much magma entered or left these respective reservoirs during this time. Finally, we conclude that magma cannot be transferred between the two reservoirs efficiently, which controls the total amount of magma that can erupt at Ambrym. Key Points: At least two deformation sources were active at Ambrym volcano between the 2018 and 2022 eruptionsLava lake drainage caused closed‐system activity in 2019, resulting in uplift from ≥0.122 km3/year of magma inflow into a tilted reservoirParameter space exploration of a theoretical model indicates that the two distinct reservoirs are not efficiently hydraulically connected [ABSTRACT FROM AUTHOR]

The past decades have seen tremendous advances in analytical capabilities regarding the sensitivity, spatial selectivity, and instrumental precision of U-Th-Pb zircon geochronology. Along with improved zircon pretreatment to mitigate the effects of Pb-loss, these advancements have resulted in the emergence of U-Th-Pb dating as the most widely used geochronometer. In parallel, it became increasingly obvious that modern analytical techniques can resolve zircon age dispersal beyond instrumental uncertainties and that this dispersion cannot be attributed to Pb-loss or inheritance. Hence, there is a pressing need to refine statistical procedures for displaying and interpreting dispersed age data from volcanic and plutonic rocks, where zircon ages were traditionally assigned to the quasi-instantaneous events of eruption and magma emplacement, respectively. The ability to resolve zircon age spectra, which often range over timescales of 103-106 years, also offers new opportunities to monitor magmatic processes, because zircon crystallization directly relates to the temperature and composition of its host melt. This relation is, at least for typical subalkaline melt compositions, well calibrated by multiple zircon saturation experiments, although absolute saturation temperatures derived from them can vary by tens of degrees. Moreover, zircon saturation thermometry is supported by the trace element and isotopic inventory of zircon, which records the thermochemical and compositional evolution of melts at high fidelity. Here, we first review the properties of true zircon age spectra that are defined by a statistically robust overdispersion relative to analytical uncertainties. Secondly, we evaluate existing models and present new models that aim to quantitatively translate the properties of zircon age spectra into parameters controlling the longevity and thermal evolution of crustal magma bodies such as magma recharge flux and duration. These developing approaches, which aspire to capture all processes that affect the formation and dispersal of zircon in dynamic crustal magma systems, have the potential to foster an improved understanding of magmatism with implications for volcanic hazard assessment, geothermal energy uses, and the origins of ore deposits. [ABSTRACT FROM AUTHOR]

The Jurassic Chon Aike Silicic Large Igneous Province (Patagonia and the Antarctic Peninsula) is dominated by voluminous, crust-derived magmas (235,000 km³) that erupted as predominately explosive silicic material over ~40 m.y. In this study, we combine petrological descriptions and bulk-rock major- and trace-element compositions with quartz oxygen-isotope measurements from multiple silicic units (primarily ignimbrites and some rhyolitic flows) from two of the five silicic formations in Patagonia. We have identified that quartz oxygen-isotope values are high (>9°-12°). Quartz phenocrysts analyzed by secondary ion mass spectroscopy (SIMS) are also homogeneous at the microscale with no measurable change in isotope value with respect to internal and often complex zoning textures. The ubiquity of widespread high d18O rhyolites and their trace-element compositions support their origin from melting of a metasedimentary source with a similarly high d18O value. Mass balance calculations require that an average of >75% melt derived from partial melting of the dominant basement lithology is needed to explain the isotopic and chemical composition of the rhyolites. The ideal P-T environment was identified by thermodynamic models for fluid-absent melting of graywackes at 900 °C and 5 kbar. Regional-scale crustal melting occurred during a widespread, high heat-flux environment within an extensional setting during the breakup of the Gondwanan supercontinent. The overlap of a unique tectonic and igneous environment, combined with a fertile crust dominated by graywacke and pelitic compositions in southern Patagonia, generated large volumes of some of the highest d18O silicic magmas documented in the geologic record. [ABSTRACT FROM AUTHOR]

The chemistry of erupted clinopyroxene crystals (±equilibrium liquids) have been widely used to deduce the pressures and temperatures of magma storage in volcanic arcs. However, the large number of different equations parameterizing the relationship between mineral and melt compositions and intensive variables such as pressure and temperature yield vastly different results, with implications for our interpretation of magma storage conditions. We use a new test dataset composed of the average Clinopyroxene-Liquid (Cpx-Liq) compositions from N = 543 variably hydrous experiments at crustal conditions (1 bar to 17 kbar) to assess the performance of different thermobarometers and identify the most accurate and precise expressions for application to subduction zone magmas. First, we assess different equilibrium tests, finding that comparing the measured and predicted Enstatite-Ferrosillite and KD (using Fet in both phases) are the most useful tests in arc magmas, whereas CaTs, CaTi and Jd tests have limited utility. We then apply further quality filters based on cation sums (3.95–4.05), number of analyses (N > 5) and the presence of reported H2O data in the quenched experimental glass (hereafter 'liquid') to obtain a filtered dataset (N = 214). We use this filtered dataset to compare calculated versus experimental pressures and temperatures for different combinations of thermobarometers. A number of Cpx-Liq thermometers perform very well when liquid H2O contents are known, although the Cpx composition contributes little to the calculated temperature relative to the liquid composition. Most Cpx-only thermometers perform very badly, greatly overestimating temperatures for hydrous experiments. These two findings demonstrate that the Cpx chemistry alone holds very little temperature information in hydrous systems. Most Cpx-Liq and Cpx-only barometers show similar performance to one another (mostly yielding root mean square errors [RMSEs] of 2–3.5 kbar), although the best Cpx-only barometers currently outperform the best Cpx-Liq barometers. We also assess the sensitivity of different equations to melt H2O contents, which are poorly constrained in many natural systems. Overall, this work demonstrates that Cpx-based barometry on individual Cpx only provides sufficient resolution to distinguish broad storage regions in continental arcs (e.g. upper, mid, lower crust). Significant averaging of Cpx compositions from experiments reported at similar pressures can reduce RMSEs to ~1.3–1.9 kbar. We hope our findings motivate the substantial amount of experimental and analytical work that is required to obtain precise and accurate estimates of magma storage depths from Cpx ± Liq equilibrium in volcanic arcs. [ABSTRACT FROM AUTHOR]

Apatite can incorporate significant amounts of H2O and CO2, potentially recording volatile abundance and behavior during magma evolution. Here we conducted in situ measurements of CO2 and H2O concentrations in apatite, along with elemental compositions, from two contemporaneous alkaline volcanic suites (Tianbao and Tudiling) in the South Qinling belt in central China to better understand the CO2 and H2O contents and behavior in evolving alkaline melts. Apatite from alkali basalts in Tianbao contains variable CO2 contents ranging from <100 ppm to 2.7 wt.% and H2O contents ranging from 0.1 to 0.6 wt.%. Apatite from REE-enriched trachytes, which evolved from alkali basalt, shows significantly lower CO2 contents and a continuous decrease in H2O during magma fractionation. The observations suggest that CO2 loss commenced at the early stages of magma evolution, whereas significant H2O loss occurred during subsequent magma fractionation in tandem with REE-enrichment. In comparison, apatite grains from the Tudiling trachyte, which is genetically linked with carbonatite, contain higher CO2 contents (0.6 to 1.5 wt.%) but lower REE concentrations than the Tianbao trachytes. Apatite in the Tudiling trachyte is inferred to have crystallized from a carbonated alkaline magma prior to significant CO2 loss and the separation of Tudiling carbonatitic melts, where subsequent liquid immiscibility led to REE enrichment into the carbonatitic melts. The volatile characteristics of apatite from the two volcanic suites provide valuable insights into two different evolutionary processes of alkaline/carbonatitic magmas, the behavior of CO2 and H2O, and the enrichment of REE in alkaline systems. [ABSTRACT FROM AUTHOR]

In recent studies of crustal growth using global zircon Hf–O isotopic datasets, high-δ18O zircons are typically attributed to intra-crustal reworking during which very little juvenile mantle-derived magmas were added to the crust. Although arc magmas may originate from a high-δ18O mantle wedge, it has been difficult to decipher the contribution of high-δ18O mantle to zircon-saturated felsic magma due to superimposed intra-crustal processes. We address this issue by combining the data from high-δ18O zircon-bearing ultramafic cumulates and coeval lavas from a Cretaceous magmatic arc in southern Tibet. The cumulates mainly consist of different proportions of cumulus olivine and intercumulus amphibole. Amphibole analyses show a transition from increasing to decreasing Zr with increasing SiO2 (50–74 wt.%) contents in the intercumulus melts, indicating zircon saturation in late-stage interstitial melts. The εNd(t) values (2.4 ± 1.4) of the apatite grains crystallized before and after zircon remain almost constant. Interstitial zircons have δ18O (6.1–7.2‰) values similar to the earliest crystallized olivine (δ18O = 6.3–7.1‰) in the cumulates. The coeval lavas may represent the intercumulus melts extracted from amphibole-rich cumulates at different depths. Both the lavas and cumulates were ultimately derived from high-δ18O arc mantle modified by small amounts (<12%) of subducted sediments, and crystallized zircon during intra-crustal magma evolution without involving crustal contamination or melting. These high-δ18O zircons therefore are not products of crustal reworking, but record crustal growth during their crystallization (110 ± 2 Ma). Our study shows that the combination of zircon and olivine oxygen isotopes for ultramafic to felsic rocks is more effective than zircon data alone in evaluating the role of crustal growth vs. reworking in an arc system. The implication is that global zircon-based crustal evolution models that attribute all high-δ18O zircons to crustal reworking may conceal recent crustal growth. [ABSTRACT FROM AUTHOR]

SUMMARY: Unzen volcano, located on Shimabara Peninsula, Nagasaki, Japan, is an active volcano that has been intensively monitored since 1989, one year before the most recent eruption in 1990–1995. Previous earthquake and surface deformation studies have revealed that magma is transported obliquely from a magma reservoir beneath Tachibana Bay, to the west of Shimabara Peninsula. Here, we conduct broad-band magnetotelluric (MT) surveys at 99 sites around Shimabara Peninsula to investigate the crustal structure beneath Unzen volcano that is related to magma migration. A 3-D resistivity model that is constructed from 25 broad-band MT sites and 45 telluric sites shows a broad high-resistivity zone beneath Shimabara Peninsula and low-resistivity zones to the west and east of the peninsula. An unexpected observation is the spatial alignment of the high-resistivity zone with a seismic low-velocity zone (LVZ) at 3–15 km depth.  Quantitative analysis indicates this high-resistivity zone contains < 0.7 per cent melt under the assumption that the melt is stored in a good porosity network, while < 11 per cent melt in relatively poor pore network. We infer this high-resistivity, LVZ to be a highly crystallized mush zone (HCMZ) with low permeability. The hypocentres and pressure sources of the 1990–1995 eruption are distributed along the boundary between the high- and low-resistivity zones beneath the western part of the peninsula. We therefore conclude that the magma migrated along a structural boundary that possessed a relatively high permeability. Previous studies have suggested that eruptible magma is usually transported vertically upward through the centre of the mush zone, whereas the present results reveal that magma can be transported along the upper boundary of an HCMZ. [ABSTRACT FROM AUTHOR]

There are several different models for the origin of syenites, but the role of magma mixing in the formation of syenites remains unclear. The Wulingshan alkaline complex in the northern North China Craton consists mainly of porphyritic syenite and syenite with abundant enclaves. These enclaves may provide new insights into the petrogenesis of syenites. We obtained zircon U–Pb age, mineral chemistry, whole‐rock major and trace elements, and Sr–Nd isotopic data for the enclaves and their host rocks to constrain the petrogenesis and identify the role of magma mixing during the formation of the different syenites in the Wulingshan alkaline complex. The results of zircon U–Pb dating indicate that the enclaves and host rocks crystallized contemporaneously at ca. 133 Ma. The enclaves contain abundant clinopyroxene, amphibole, and biotite, and their average Nb/Ta (18.46) and Th/Ce (0.04) ratios are similar to those of the mantle. The enclaves have relatively high Fe2O3T, MgO, and CaO contents, and their SiO2 contents are equivalent to those of intermediate rocks, indicating that they formed by mixing the mafic and felsic magmas to some extent. The different mineral assemblages, major and trace elements and isotopic compositions of the enclaves in the porphyritic syenite and syenite indicate that they are two batches of parental magma with different properties derived from the mantle. The porphyritic syenite and syenite have high SiO2 and low Fe2O3T, MgO, and CaO contents, as well as low V, Cr, Co, and Ni contents. These major and trace element characteristics of the host rocks require the involvement of crustal components. The Sr–Nd isotopic compositions of the enclaves and the host syenitoids plot on a mixing curve between enriched lithospheric mantle and lower crust, indicating that these rocks are the products of magma mixing and crust–mantle interaction. Considering the contact relationships, the geochemistry data, and the mixing model presented in the paper, we propose that the upwelling of the hot asthenosphere heated the overlying enriched lithospheric mantle and triggered low‐degree partial melting. The alkalic mafic magmas derived from enriched mantle sources were mixed with felsic magmas generated by partial melting of the lower (or upper) crust to form the different syenites. [ABSTRACT FROM AUTHOR]

Volatile element abundance is a crucial factor triggering mineralization and controlling the enrichment of molybdenum in porphyry deposits. The Chalukou deposit is the largest porphyry Mo deposit in NE China, with an average grade of 0.087% Mo. In this contribution, we present petrology, bulk geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes, and apatite geochemistry for the Chalukou deposit. The intrusive rocks include pre‐mineralization monzogranite, syn‐mineralization quartz porphyry, fine‐grained porphyry and granite porphyry, and post‐mineralization monzogranite and feldspar porphyry. These granitoids are metaluminous to peraluminous, and belong to alkali‐calcic to calc‐alkalic series. Zircon εHf(t) values of granitoids range from +0.2 to +5.7 with corresponding Hf crustal model ages of 805–1170 Ma, indicating a Mesoproterozoic juvenile crustal source modified by mantle‐derived magma. They are characterized by logf(O2) of −16.1 to −9.4, with an average of −12.5, ΔFMQ of +0.8 to +7.9, with an average of +4.5, showing a relatively high oxidation state for the syn‐mineralization magma. The apatites in quartz porphyry have the highest F contents, ranging from 3.61 to 4.62 wt%. At Chalukou, F‐rich magma is conducive to the convection of magma and promotes the efficient separation of differentiation magma, making the magmatic‐hydrothermal fluid circulate many times, eventually resulting in the accumulation of ore‐forming materials on the top of the magma chamber and gradually aggravating mineral enrichment processes. [ABSTRACT FROM AUTHOR]

Mafic microgranular enclaves (MMEs) are a ubiquitous feature of post-collisional magmatism, receiving much attention among earth scientists over the last decades. While recent advances point to the large-scale involvement of the lithospheric mantle in granite petrogenesis, MMEs have received less attention in such discussion. Because MMEs are commonly acknowledged to represent the mafic end member with a mantle affinity that is related to early-stage batholith petrogenesis, they constitute a good proxy for the mantle role in the process. Using MME data from Los Pedroches batholith in southwestern Iberia, we conduct a geochemical comparative study between MMEs and the mafic-intermediate (sanukitoid) suite of post-collisional batholiths. An accurate overlap between the two groups is revealed, implying a potential genetic link between MMEs and the sanukitoid suite. Together with evidence from experimental cotectic liquids, the link between the high-Mg signature of postcollisional magmas and the predominance of amphibole in the studied MME samples is used to account for the composition of post-collisional magmatism. Implications for post-collisional batholith petrogenesis is then discussed in a qualitative manner, suggesting a heterogeneous yet common two-stage origin for all post-collisional magmatism in which the relationship between MMEs, sanukitoid, and the host felsic magmas is a differentiation process, thus representing a major input of juvenile magma into the crust. [ABSTRACT FROM AUTHOR]

Apatite is a ubiquitous phase in granite plutons and in most adjacent country rocks, thus contamination of a granite magma with wall-rock material results in two genetic types of apatite in the magma: cognate and foreign. These two textural and chemical varieties of apatite undergo textural and compositional changes to reach physical and chemical equilibrium (perfect assimilation) in the melt. Our experiments replicate the conditions in such contaminated granites. The starting materials consist of a peraluminous synthetic SiO2-Al2O3-Na2O-K2O (SANK 1.3) granite gel with A/NK of 1.3, synthetic F-apatite, synthetic Cl-apatite, and natural Durango apatite. Initial experiments in cold-seal hydrothermal pressure vessels at magmatically realistic temperatures of 750 °C and pressures of 200 MPa produced negligible reactions, even after run times of 2000 h. Instead, we used an argon-pressurized internally heated pressure vessel with a rapid-quench setup at temperatures of 1200 °C, pressure of 200 MPa, and run durations of 192 h. An advantage of this high temperature is that it exceeds the liquidus for quartz and feldspar; therefore, apatite is the only solid phase in the run products. The starting composition of each run was 90 wt% SANK 1.3 granite gel and 10 wt% crushed apatite (consisting of one, two, or three varieties), with and without 4 wt% added H2O. Run products were examined by SEM for texture and by EMPA and LA-ICP-MS for composition. The starting synthetic granite composition contains no Ca, F, Cl, or REEs thus, in every run, apatite was initially undersaturated in the melt. In all experiments, most large apatite grains consisted of anhedral shards with rounded corners, most small apatite grains were round, and a small proportion of apatite grains developed one or more crystal faces. In experiments with two or three apatite compositions, the run-product apatite grains had compositions intermediate between those of the starting-material grains, and they were homogeneous with respect to Cl, and probably F, but not with respect to REEs. The processes to reach textural equilibrium consist of dissolution until the melt is saturated in apatite, followed by Ostwald ripening to eliminate small grains and to develop crystal faces on larger ones. The processes to reach chemical equilibrium consist of dissolution of apatite, diffusion of cations (Ca, P, REE) and anions (F, Cl, OH) through the silicate melt, and solid-state diffusion in the undissolved apatite grains. The halogens approached chemical equilibrium in all experiments, but in the experiments containing Durango apatite, the REEs have not. Models involving radial diffusion into spherical apatite grains at the temperatures of the experiments show complete re-equilibration of the halogens, but changes in the REE concentrations affecting only the outer few micrometers. We conclude that the rate of chemical equilibrium for the halogens is greater than the rate of physical equilibrium for texture, which in turn is greater the rate of chemical equilibrium for REEs. We illustrate these processes with a natural example of contaminated granite from the South Mountain Batholith in Nova Scotia. Given that all granites are contaminated rocks, we propose that future petrogenetic studies focus on developing techniques for a minerals-based quantitative estimation of contamination (QEC). [ABSTRACT FROM AUTHOR]

Arc magmatism is fundamental to the generation of new continental or island arc crust. However, the mechanisms that add to the chemical complexity of natural calc-alkaline magmas ranging from basaltic to rhyolitic compositions are debated. Differentiation mechanisms currently discussed include magma mixing, assimilation, crustal melting, or (fractional) crystallisation. In this contribution, the differentiation of arc magmas by decompression-driven crystallisation is investigated. We performed a set of equilibrium crystallisation experiments at variable crustal pressures (200–800 MPa) on a hydrous high-Al basalt (3.5 wt.% of H2O in the starting material) with run temperatures varying from near-liquidus conditions (1110 °C) to 900 °C. Oxygen fugacity was buffered at moderately oxidising conditions close to the NNO equilibrium. Combining these novel experiments with previous polybaric fractional crystallisation experiments (Marxer et al., Contrib Mineral Petrol 177:3, 2022) we demonstrate the effects of pressure on the crystallisation behaviour of calc-alkaline magmas with respect to liquid and cumulate lines of descent, mineral chemistry, and phase proportions. Decompression shifts the olivine-clinopyroxene cotectic curve towards melt compositions with higher normative clinopyroxene and enlarges the stability field of plagioclase. This exerts a key control on the alumina saturation index of residual liquids. We argue that near-adiabatic (or near-isothermal) decompression accompanied by dissolution of clinopyroxene entrained during residual melt extraction in the lower crust keeps arc magmas metaluminous during crystallisation-driven differentiation thereby closely reproducing the compositional spread observed for natural arc rocks. [ABSTRACT FROM AUTHOR]

Large volume, intermediate-felsic magma reservoirs are the source of melt and mineralising fluids which generate porphyry copper deposits. Cooling and crystallisation of hydrous magmas drives the exsolution and expulsion of a magmatic volatile phase—a process which remains challenging to constrain in porphyry Cu systems where the record of magma volatile compositions is rarely preserved. Here, we use the halogen compositions of apatite inclusions shielded as inclusions within zircon to constrain volatile evolution in magma reservoirs which pre-date and are synchronous with porphyry Cu mineralisation at Quellaveco, Southern Peru. Geochemical and textural data confirm that the zircon-included apatites escaped re-equilibration with hydrothermal fluids, unlike apatites found in the groundmass of the same rocks. We, therefore, recommend that future studies attempting to reconcile magmatic volatile budgets using apatite in porphyry Cu systems should focus on apatite inclusions in zircon. By combining the apatite inclusion data with numerical modelling, we find evidence that the magma reservoir sourcing porphyry Cu mineralisation remained fluid-saturated for the entire period recorded by apatite crystallisation. By contrast, the pre-mineralisation batholith shows more variable, potentially fluid-undersaturated behaviour. Our modelling suggests that in order to attain the porphyry melt volatile compositions inferred from apatite, the magma reservoir must have exsolved a large proportion of its volatile budget, consistent with having been held at high crystallinity (40–60% crystals). This crystallisation interval coincides with peak chlorine and copper extraction from intermediate-felsic magmas, and would have permitted efficient fluid migration and accumulation at the roof of the system. We suggest that the storage of large-volume, long-lived, crystal-rich magma reservoirs in magmatic arcs may be a critical step in generating world-class porphyry copper deposits. [ABSTRACT FROM AUTHOR]

The Azores region straddles the Mid-Atlantic Ridge and comprises volcanic islands and seamounts interspersed with non-magmatic oceanic basins arranged along subparallel slow-spreading systems. The cross-check of CO2-rich fluid inclusions barometry from lavas and tephras erupted during the last 20 ka with the sources of seismicity of the last 22 years traced the deepest magma accumulation zone at a regional scale. These zones are considered to represent the boundary between the dense rocks of magma systems and the lithospheric mantle. This boundary is at a depth range of ~ 17 to 20 km beneath the islands close to the Mid-Atlantic Ridge, which are younger than 500 ka, and up to ~ 29.4 km beneath the eastern island of S. Miguel, younger than 800 ka and the nearby Dom João de Castro Seamount and the Hirondelle Basin. The same method has been applied to the ~ 2 Ma-old volcanic products of Flores, the ~ 1.9 Ma old S. Jorge and the 5 Ma-old lavas of Santa Maria. Results revealed a depth of ~ 30.5 km beneath the Flores and ~ 26 km beneath the ~ 1.9 Ma-old S. Jorge. These two islands are west and east of the Mid-Atlantic Ridge, within 200 km. Finally, the crust-mantle transition has been found below Santa Maria, the easternmost island, ~ 500 km away from the Mid-Atlantic Ridge at a depth of ~ 33 km. Overall, repeated mafic magma injections at the base of each magma system generated vertically stacked layered ultramafic mush bodies, which thickened the crust overtime. [ABSTRACT FROM AUTHOR]

The Azufre volcano (21°47′S; 68°14′W) is emplaced above the western boundary of the Altiplano Puna Magma Body. The youngest lava of the Azufre volcano (50–331 ka) was selected for detailed studies because of the relevant petrological information that could emerge to understand its reservoir as a potential heat source of the neighboring Cerro Pabellón geothermal system. The studied lava corresponds to an andesite-dacite (61–63 SiO2 wt%) with phenocrysts of plagioclase, amphibole (Group 1), biotite, pyroxenes, quartz, and olivine. The lava also contains aphanitic enclaves (58–60 SiO2 wt%), whose groundmass have the same mineralogy of lava samples groundmass consisting of amphibole microphenocryts (Group 2) and microlites of plagioclase, pyroxenes, and Fe–Ti oxides. Disequilibrium textures are commonly observed in the studied samples such as partially resorbed plagioclase phenocrysts, amphibole breakdown, and reverse zoning in pyroxene and plagioclase phenocrysts. Thermobarometry calculations indicated pressures of ~ 2 kbar for Group 1 amphiboles, temperatures of 905–1097 °C for Mg-rich pyroxene phenocrysts and Ca-rich plagioclase (An ≥ 66), and near-solidus temperatures of 712–788 °C for Group 1 amphibole-plagioclase pairs. Group 1 amphiboles also indicate crystallization from an evolved liquid (63–79 wt% of SiO2). Oxidation conditions of QFM + 0.9–2.5 log units were recorded in amphibole and Fe–Ti oxides. Rhyolite-MELTS models reproduce the composition of the high-temperature phases from a melt composition (andesitic enclave) at similar P–T-fO2. The arrival of new hot andesite magma into a crystal-rich shallow reservoir, thermally and compositionally zoned, would have triggered the studied eruption. Diffusion models in Fe–Ti oxides microlites indicated cooling temperatures of 742–866 °C during the sub-aerial emplacement of the lava. [ABSTRACT FROM AUTHOR]

The positive Ti isotope versus SiO2‐content correlation in igneous rocks reflects the fractional crystallization of Ti‐bearing oxide minerals. However, Ti isotope variations of subduction‐related igneous rocks indicate that the Ti isotope compositions of their mantle sources are heterogeneous and additional mineral phases may promote Ti isotope fractionation. We have determined the Ti isotope composition of well‐characterized subduction‐related basalts, andesites and boninites. Samples from the Solomon Islands, the Troodos ophiolite in Cyprus, and Cape Vogel in Papua New Guinea show small but resolvable variations that may be related to differences in their mantle sources. Specifically, the δ49Ti of boninites (+0.109‰ to +0.168‰) is slightly higher than that of tholeiites (−0.027‰ to +0.111‰) from the same localities (Troodos in Cyprus and Cape Vogel in Papua New Guinea). Modeling suggests the partial melting of progressively depleted mantle sources where residual Cr‐spinel plays a greater role in controlling the Ti budget during partial melting. More pronounced variations in δ49Ti are clearly linked to the fractional crystallization of Ti‐oxides: Samples from Rabaul Volcanic Complex (New Britain, Papua New Guinea) show increasing δ49Ti (up to +0.373‰) with increasing Ti/V and decreasing Dy/Yb. Fractional crystallization models suggest that oxide minerals and amphibole are needed to sufficiently increase the δ49Ti of these magmas. Our study highlights that the combination of diagnostic trace element patterns and Ti isotope compositions in subduction‐related igneous rocks can be a powerful tool to constrain petrogenetic processes and to discriminate between different crystallizing mineral phases. Plain Language Summary: Titanium isotope data obtained for basalts from various volcanic arc‐related settings show how the different minerals involved in their magmatic evolution influence their Titanium isotope composition. Coupled with trace element concentration data, magmatic processes are revealed that operate on either a large scale, such as along the arc in the 10 km range, or as very specific magma chamber processes. Key Points: Mass‐dependent Titanium isotope variations in arc basalts originate from fractional crystallization as well as partial meltingTrace element and isotope modeling strongly suggest that amphibole fractionates Ti isotopes in addition to magnetite or ilmenite [ABSTRACT FROM AUTHOR]

The basaltic caldera volcanoes in the Galápagos Islands characteristically erupt lavas via summit circumferential and radial flank dike intrusions, but the underlying magma plumbing systems remain enigmatic. Here, we document surface displacements of Wolf volcano using interferometric synthetic aperture radar (InSAR) data from 2015 to 2022. We show that Wolf volcano experienced 6‐years of continuous inflation after the 2015 eruption, followed by a shallow flank eruption in January 2022. The deformation is modeled with a vertical caldera ring‐fault and a radial dike on the southeast flank. The ring‐fault underwent opening and reverse faulting during the inflation period, and closure and normal faulting during and after the eruption. Stress interactions between the ring‐fault and the flank dike suggest the asymmetric opening of the ring‐fault promotes flank eruptions. The best‐fit deformation model differs from the previous models and offers an alternative view of how magma is fed into radial dikes during flank eruptions. Plain Language Summary: The 2022 eruption at Wolf volcano in the Galápagos Islands started from a radial fissure on the SE flank, which was different from the 2015 eruption that mainly occurred inside the caldera. We track the sequence of ground deformation before, during and after the 2022 eruption using InSAR data. We find that Wolf volcano experienced continuous inflation before the 2022 eruption, followed by deflation during and after the eruption, resulting in complex ground deformation within and beyond the caldera and on the SE flank. We propose a model with ring fault slip and opening/closure to explain the observed ground deformation within the caldera. We find that opening and reverse slip of the ring fault can explain the inflation before the 2022 eruption, while closure and normal slip caused the deflation period during and after the eruption. The asymmetric opening of the ring fault changed the stresses in the volcano and promoted the occurrence of the flank eruption. Our model is different from the dike rotation model that was proposed for Fernandina volcano and may allow for improved forecasts of the location and style of future eruptions on the Galapagos Islands. Key Points: Interferometric synthetic aperture radar data are used to study ground deformation before, during and after the 2022 Wolf eruptionA ring fault opening/closure model fits ground deformation of the caldera wellAsymmetric opening of the ring fault promotes flank eruptions at Wolf volcano [ABSTRACT FROM AUTHOR]

We have carried out in situ high‐pressure acoustic velocity measurements of (Fe2+, Al)‐bearing MgSiO3 glass up to pressures of 155 GPa, which confirmed a distinct pressure‐induced trend change in the transverse acoustic velocity (VS) profile around 98 GPa, likely caused by the Si‐O coordination number (CN) change from 6 to 6+. Although it has been reported that the substitution of Fe2+ in MgSiO3 glass induces almost linear velocity reduction up to ∼160 GPa, we revealed that the VS profile of (Fe2+, Al)‐bearing MgSiO3 becomes anomalously steeper above ∼100 GPa and eventually came to be equivalent to MgSiO3 glass above ∼125 GPa. This implies the incorporation of Al into Fe‐bearing MgSiO3 glass significantly facilitates making it far elastically stiffer and thus the densification under pressures well within the Earth's lower mantle. Our results indicate the possible presence of stiff and highly dense silicate melts in deep MOs in the rocky terrestrial planets. Plain Language Summary: Since the terrestrial planets are thought to have gone through multiple episodes of magma ocean (MO) in their formation processes, clarifying the structure and physical properties of silicate melts under relevant deep MO conditions is crucial to understanding the internal structure and evolution of the terrestrial planets. Our in situ high‐pressure acoustic velocity measurements of (Fe2+, Al)‐bearing MgSiO3 glass, used as a structural analog of silicate melts, shows both Al and Fe2+ are very effective to reduce the pressure corresponding to the Si‐O CN change from 6 to 6+. In addition, a few percentages of Al incorporation could make the Fe‐bearing MgSiO3 glass significantly far elastically stiff and thus dense with 6+ CN in Si‐O in the deep terrestrial interiors. The presence of stiff and highly dense silicate melts in deep MOs in the terrestrial planets would offer essential insights into the MO convection, gravitational stability of silicate melts in the course of MO crystallization, and the mantle stratification of the terrestrial planets. Key Points: We have carried out acoustic wave velocity measurements of (Fe2+, Al)‐bearing MgSiO3 glass up to 155 GPaVS profile displays a change at 98 GPa induced by the Si‐O coordination number change from 6 to 6+ followed by anomalously steeper trendResults indicate the possible presence of highly dense Al, Fe2+‐bearing Si‐rich melts in the deep terrestrial magma oceans [ABSTRACT FROM AUTHOR]

Mount Elbrus, Europe's tallest and largely glaciated volcano, is made of silicic lavas and is known for Holocene eruptions, but the size and state of its magma chamber remain poorly constrained. We report high spatial resolution U–Th–Pb zircon ages, co-registered with oxygen and hafnium isotopic values, span ~ 0.6 Ma in each lava, documenting magmatic initiation that forms the current edifice. The best-fit thermochemical modeling constrains magmatic fluxes at 1.2 km3/1000 year by hot (900 °C), initially zircon-undersaturated dacite into a vertically extensive magma body since ~ 0.6 Ma, whereas a volcanic episode with eruptible magma only extends over the past 0.2 Ma, matching the age of oldest lavas. Simulations explain the total magma volume of ~ 180 km3, temporally oscillating δ18O and εHf values, and a wide range of zircon age distributions in each sample. These data provide insights into the current state (~ 200 km3 of melt in a vertically extensive system) and the potential for future activity of Elbrus calling for much-needed seismic imaging. Similar zircon records worldwide require continuous intrusive activity by magmatic accretion of silicic magmas generated at depths, and that zircon ages do not reflect eruption ages but predate them by ~ 103 to 105 years reflecting protracted dissolution–crystallization histories. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of suturing and cratonisation and their implications are vital in estimating the link between the lithospheric mantle architecture and geothermal resources. We propose new interpretations of the Western Arabian Shield's geodynamic styles and geothermal anomalies. In this work, features of the crust and mantle were interpreted from geophysical modeling to unravel the structural dynamics between the Arabian Shield and the Red Sea rift, as well as the influence of these mechanisms on the uplift of the Cenozoic basalts. Estimates of the lower crust thermal properties were also achieved. Spectral properties of the potential field were used to define the Curie isotherm, heat fluxes, geothermal gradients, radiogenic heat production, Moho configuration, and lithosphere-asthenosphere boundary. Results show new structural styles, micro-sutures, and significant thermal anomalies. The defined geothermal patterns were inferred to be due to localized initiation of tectonic and asthenospheric disequilibrium during the rifting episodes within the Red Sea. Also, magma mixing is initiated by the northward migration of magma from the Afar plume towards the Western Arabian Shield which drives local mantle melts beneath the western Arabia, thereby providing the pressure field required for magma ascent. The ascendant magma flow provides the heating source of geothermal reservoirs within the Western Arabian Shield. However, there are indications that during the episodes of rifting within the Red Sea and/or ancient Pan-African activities, the mixing process may have been altered resulting in crustal thinning and creating pathways of ascendant magma flow along the MMN volcanic line. Integrating geophysical and geothermal models indicated new zones of suturing and extensional tectonics between the amalgamated terranes. The geodynamic interpretation shows a new redistribution of terranes and continuous compressional and transtentional movements within the Arabian Shield. [ABSTRACT FROM AUTHOR]

The article provides information on the transition from carbonatitic magmas to hydrothermal brines in carbonatite systems, which are important sources of rare earth elements (REEs). The study investigates the pressure-temperature-composition properties of the Na2CO3-H2O system and shows that under high-pressure and high-temperature conditions, Na2CO3 melts transition into hydrothermal brines, leading to the enrichment of REEs in the brine-melts and the formation of economic ore bodies.

A seismic swarm affected the 53.3°–54.3° Latitude North section of the Mid‐Atlantic Ridge from 26 September to 10 December 2022. We rely on regional, teleseismic and array data to relocate 61 hypocenters and derive 77 moment tensors. The 2022 swarm released a cumulative moment equivalent to Mw 6.3. Seismicity was shallow (7 ± 3 km depth). Most earthquakes are located along the ridge axis with typical, NS oriented normal faulting mechanisms, but a few among the largest and latest earthquakes have unusual thrust mechanisms and locations as far as ∼25 km from the ridge. We attribute the swarm to a shallow magmatic intrusion, with a vertical dike first propagating ∼60 km along axis, accompanied by shallow normal faulting, and then thickening and triggering thrust earthquakes off the ridge, in response to compressive stress buildup. The unrest provides a rare example of an energetic, magmatic driven swarm episode at the mid‐ocean ridge. Plain Language Summary: The largest plate boundary systems on Earth are Mid‐ocean ridges (MOR), where the plates continuously drift apart and new lithosphere is constantly being formed. Although the process is well understood, we rarely detect spreading events at MOR, mainly because these regions are remote and local monitoring is rarely possible. In September–November 2022 a large, unusual seismic swarm occurred along a spreading center ridge segment of the North Mid‐Atlantic Ridge. Despite the remoteness of the region, we managed to model regional and teleseismic data to perform earthquake relocation, depth estimation and moment tensor inversion. In this way, we could reconstruct the geometry and the evolution of the seismicity. We found that in the early days of the swarm, seismicity migrated unilaterally over ∼60 km along the ridge axis, from North to South, triggering normal faulting earthquakes, which are typical at MOR. Later, large thrust mechanisms, anomalous in an extensional environment, appeared and quickly became predominant. We explain seismological observations by a magmatic intrusion, which first propagated southward, producing shallow normal faulting earthquakes above the vertical magma dike, and later thickened, increasing compressional stresses on its sides, and triggering large thrust earthquakes. Key Points: Analysis of a short, intense seismic swarm at the Mid‐Atlantic RidgeIdentification of unusual, thrust focal mechanisms in an extensional environmentSwarm triggered by dike intrusion at the mid‐ocean ridge [ABSTRACT FROM AUTHOR]

Titanium diffusion profiles in quartz crystals are widely applied to constrain the duration of magmatic processes. However, experimentally determined Ti diffusion coefficients in quartz diverge by three orders of magnitude. To rectify this problem we derive Ti diffusion coefficients from natural quartz phenocrysts from the 1991 eruption at Mt. Pinatubo, by combining U-Th ages of small (15–40 µm long) zircon inclusions with Ti diffusion profiles measured at nearby growth zone contacts in the same quartz crystals. Application of the obtained data to quartz crystals with Ti-rich rims from thirteen silicic volcanic tuffs worldwide suggests that the magmas erupted years to thousands of years after magma chamber rejuvenation, with the priming time increasing with magma volume and decreasing temperature. Here we show that the time scales involved in the generation of silicic volcanic eruptions are much longer than originally thought. Titanium diffusion profiles in quartz record the duration of magmatic processes. Here, the authors use a novel way to constrain Ti diffusion coefficients and apply them to determine the time scales involved in the priming of volcanic eruptions. [ABSTRACT FROM AUTHOR]

The article focuses on understanding the drivers of volcanic eruptions and their impact on eruption style using rapid, high-resolution matrix geochemical analysis. It mentions by analyzing samples from the 2021 La Palma eruption, the study reveals distinct pulses of basanite melt driving the onset, restart, and evolution of the eruption.

Mafic magmatic enclaves (MMEs) hosted in granitic plutons are ideal to investigate the role of mushes on magma mixing processes in crustal magma chambers. However, the petrographic evidence for mixing of magmas through infiltration and percolation in coexisting mushes and magmas is desired. Here, we describe complex zoning patterns of plagioclase in the MMEs hosted in the monzogranite of the Early Cretaceous Sanguliu pluton in East China to reveal a mush-facilitated magma mixing process. The MMEs appear as round to oval nodules about 10 to 20 cm in size and show diverse disequilibrium textures. Plagioclase in the MMEs can be identified as three populations (Plag1, Plag2, and Plag3) with distinct zoning patterns, anorthite contents (X An) and initial Sr isotopic ratios (87Sr/86Sri). Plag1 is antecryst displaying normal zoning with An42–67 in the core and An20–36 in the mantle. The core of Plag1 shows coarse sieve texture with high-frequency oscillation in the margin, and the mantle displays resorption surface and patchy zoning. Plag2 is also antecryst with An23–66 in the core and An21–35 in the mantle. However, its core can be further recognized as Core I inside and Core II outside with distinctly different An23–43 and An44–66, respectively, showing reverse zoning. In addition, Core I contains aligned biotite inclusions and Core II shows sieve texture, resorption surface and patchy zoning. Amphibole inclusions are sporadically enclosed within Core I of Plag2 (Amp1) and mantles of Plag1 and Plag2 (Amp2), but rarely observed in Core II of Plag2. Plag3 is anhedral grain in the matrix and shows core-rim texture with An20–37 in the core. The three plagioclase populations all exhibit angular rims with resembling An9–22. Plag1 core and Plag2 Core II have (87Sr/86Sr)i (0.70920 to 0.71092) similar to the bulk (87Sr/86Sr)i of the mafic dykes intruding the Sanguliu pluton, and likely crystallized from basaltic andesitic magmas. In contrast, the rims of Plag1, Plag2, and Plag3 overall have (87Sr/86Sr)i (0.71391 to 0.71583) nearly identical to the (87Sr/86Sr)i of host monzogranite and the plagioclase in the monzogranite, likely crystallized from granitic magmas. The mantles of Plag1 and Plag2 and the core of Plag3 have (87Sr/86Sr)i (0.71141 to 0.71390) overlapping the (87Sr/86Sr)i of the MMEs, and may have crystallized from mixed melts. Calculation results based on amphibole thermobarometers show that Amp1 crystallized at ~775 °C and ~ 16 km depth, whereas Amp2 and the amphibole in the matrix of the MMEs and monzogranite crystallized at 730 to 744 °C and 8 to 9 km depth. We thus propose that the chemical and textural complexity of the three plagioclase populations in the MMEs can be attributed to that the MMEs may have come from a mushy hybrid layer that was developed through a molten granitic body being recharged by upwelling basaltic andesitic magma. Core I of Plag2 may have nucleated and grown from andesitic magma that was evolved from the basaltic andesitic magma from which the core of Plag1 and Core II of Plag2 crystallized. The two types of antecrystic plagioclase then may have experienced resorption and disequilibrium growth in the hybrid layer, and finally rimmed with ambient, evolved interstitial melt within mushy MMEs. This study shows that complex zoning patterns and compositions of plagioclase populations in the MMEs hosted in granitic plutons have important bearings on mush-facilitated magma mixing processes. [ABSTRACT FROM AUTHOR]

The petrogenesis of aluminous A-type granites is a contentious subject. Here, we focused on the North Kudi pluton in the Western Kunlun orogen to investigate the origin and magmatic processes responsible for generating A-type granites. Samples from the North Kudi pluton are metaluminous to weakly peraluminous. K-feldspar granite samples are characterized by high alkali and Cl contents, high HFSE concentrations and FeO/MgO, low F content, negative Ba, Sr, P, Eu, and Ti anomalies, and high magma temperature (>903 °C), showing affinity to aluminous A-type granites. However, their 10,000 × Ga/Al ratios (1.86–3.18) are relatively lower than typical A-type granites. Quartz-monzonite displays similar Sr–Nd isotopic compositions and Ga/Al ratios with the K-feldspar granite but less pronounced negative Sr, P, and Ti anomalies and no discernable negative Ba and Eu anomalies. Fractional crystallization of alkali-rich, Cl-rich, and F-poor magmas can generate some typical geochemical characteristics of A-type granites (e.g., negative Ba, Sr, P, and Eu anomalies) but has little influence on Ga/Al ratios. The enriched Sr–Nd isotopic compositions, high Cl and alkali contents, arc-like geochemical features, and the involvement of slab-derived components, as indicated by high zircon Ce4+/Ce3+ (up to 503), suggest that the North Kudi pluton was possibly derived from partial melting of the metasomatized lithospheric mantle in the time of asthenosphere upwelling during the post-collisional stage. The emplacement of the North Kudi pluton thus indicates the onset of the post-orogenic stage in the Western Kunlun orogen. [ABSTRACT FROM AUTHOR]

To ascertain the Early-to-Middle Jurassic tectonic setting in the central Great Xing'an Range, this study investigated the Early and Middle Jurassic granitoids exposed in the Chaihe area in the central Great Xing'an Range based on isotopic chronology and petrogeochemistry. The results of this study show that the Early and Middle Jurassic granitoids have emplacement ages of 179–172 Ma. Moreover, the Early and Middle Jurassic granitoids are high-K calc-alkaline unfractionated I-type granitoids and high-K calc-alkaline fractionated I-type granitoids, respectively. The magma sources of the Early and Middle Jurassic granitoids both originated from the partial melting of newly accreted lower crustal basaltic rocks. Meanwhile, the Middle Jurassic magma sources were mixed with mantle-derived materials or ocean-floor sediments formed by the dehydration and metasomatism of subducted slabs. The Early and Middle Jurassic granitoids in the study area were formed in the subduction environment of the oceanic crust, in which the Mongol-Okhotsk oceanic plate was subducted southward beneath the Eerguna and Xing'an blocks. Moreover, the Siberian plate began to collide and converge with northeast China during the Middle Jurassic. [ABSTRACT FROM AUTHOR]

This work documents, for the first time, the calculated oxygen and hydrogen isotope composition of the brines exsolved from the peripheral margin of the active magma alkaline chamber that fed the AD 79 ("Pompei") eruption of Vesuvius. The exsolved hydrosaline fluids had a constant δ18O composition and a variable δD composition, showing a general lowering of δD at nearly constant δ18O content. We argue that the progressive fluid exsolution at the upper peripheral parts of the AD 79 magma chamber may explain this isotopic path. The modeling of the evolution of the hydrogen isotope composition of water remaining dissolved in the melt, and of the exsolved fluid as a consequence of progressive degassing, would favor multiple fluid-release events from the magmatic reservoir. A schematic model on the pulsed accumulation and release of fluids at the top of the magmatic reservoir prior to the eruption is thus proposed. The assessment of the stable isotope composition of the fluids exsolved from the AD 79 magma chamber of Vesuvius may be particularly relevant for the geochemical surveillance of the volcano as it may help to interpret the isotopic composition of fumarolic gases and its variations. [ABSTRACT FROM AUTHOR]

The Soarinho Alkaline Intrusion, southeastern Brazil, makes up part of the Serra do Mar Igneous Province, and it is composed of alkali feldspar syenite, alkali feldspar trachyte, quartz syenite, and monzonite. Geochemical and geochronological analyses of the Soarinho were compared with data from its neighbors, Rio Bonito and Tanguá. Zircon U-Pb Laser Ablation ages show that Soarinho is younger than Rio Bonito and Tanguá. Ages obtained from the monzonite (60 ± 2 Ma), alkali feldspar syenite (58 ± 2 Ma), and quartz syenite (58 ± 2 Ma) are indistinguishable within error. One nepheline syenite sample from Tanguá gives an age equal to those of Rio Bonito already published (65 ± 1 Ma). Petrographic and geochemical data show a clear contrast among Soarinho, Rio Bonito, and Tanguá. Lu-Hf isotopic data for the three alkaline intrusions (all negative) point to some similarities in their sources. The data suggest an enriched mantle source for Soarinho; however, an older continental crust contribution cannot be discarded. [ABSTRACT FROM AUTHOR]

The occurrence of Permian magmatic rocks in the Colombian Andes is restricted to a few localities. Previous works have focused mainly on explaining its tectonic setting, whereas petrogenesis has received less attention. This study closes this gap by reporting whole‐rock geochemistry, zircon U–Pb geochronology, trace elements and Hf isotopes from massive and mylonitic granitoids along central Colombia to constrain their age, source and petrogenesis. Our results show that the granitoids have a calc‐alkaline character, are rich in light‐rare elements (LREEs) and large‐ion lithophile elements (LILEs), present negative Nb and Ti anomalies, crystallized between ca. 276–265 Ma and show variable εHf(i) values ranging from −1.5 to +1.7. Combining our results with published geochemical, geochronological and isotopic data from this region, we suggest that the Middle Permian granitoids from the Tolima region were formed in a continental magmatic arc installed at the western margin of Gondwana, where partial melting of the mantle wedge and further crustal assimilation of the magmas with an old radiogenic and heterogeneous crust were essential processes for the modification of the source of the magmas that generated the granitoids. The Middle Permian may have reached the peak magmatic conditions (ca. 280–270 Ma), according to the recurrence of ages in this time interval. This period of magmatic activity may have been interrupted by the Triassic extensional period related to the beginning of the Pangea breakup. [ABSTRACT FROM AUTHOR]

Subduction zones display the most diverse magma compositions from various calc‐alkaline differentiates to alkaline mafic associations, but mechanisms generating Nb‐Enriched Basalts (NEB) and High‐Nb Basalts (HNB) in such settings have received less attention from the researchers. Occurrences of NEB and HNB magmas in the Mesozoic Neotethyan active margin in Iran, known as the Sanandaj‐Sirjan Zone, provide an excellent natural lab for examining this interesting petrologic puzzle. The Middle‐Jurassic typical calc‐alkaline arc plutons exhibit a NW‐SE subduction parallel trend. In the northwestern sector of the zone, the Late Jurassic–Early Cretaceous magmatic rocks (JCMR) define a chain that transects the Middle‐Jurassic arc trend. The two cross‐cutting magmatic chains are chemically and genetically different. The JCMR include three distinct compositional groups: (i) tholeiites that are depleted in high‐field‐strength elements (HFSE) and show subduction‐related geochemical fingerprints, (ii) NEB with higher abundances of Nb and other HFSE, and (iii) HNB with the highest abundances of Nb and other HFSE. The latter two groups do not display typical arc signatures and are transitional between arc and plume‐type magmas. These three groups of rocks show linear major and trace element, and Sr–Nd isotopic variation trends extending from Mid‐Ocean Ridge Basalts‐like tholeiites to Oceanic Island Basalts‐like HNB. Hence, a two‐component mixing process is suggested for explaining the compositional variation of the JCMR. We propose that a vertical window resulted from slab tear created the geodynamic environment for juxtaposition of magmas originated at different mantle depths and formation of the transitional basalts by magma mixing. [ABSTRACT FROM AUTHOR]

Boron is an effective tracer of fluid processes in subduction zones. High B and δ11B in arc magmas require efficient B transfer from the slab to magma source regions. The Higashi-akaishi metaperidotite body in the Sanbagawa high-pressure belt, Japan, is composed of locally serpentinized mantle wedge peridotites exhumed in a subduction channel. Cores of coarse-grained primary mantle olivine have 1-4 µg/g B, enriched compared to typical mantle olivine, and δ11B of --10%c to --1%o, consistent with incorporation of fluids from dehydrating slab at --90-120 km depth. Rims of primary mantle olivine as well as olivine neoblasts have even higher B (5-20 µg/g) and higher δ11B (--8%c to +2%o) due to incorporating slab fluids at depths of --70-100 km. Antigorite, formed below 650 °C, shows comparable δ11B and B contents as olivine rims. The data show that olivine is capable of scavenging significant amounts of B from fluids by diffusion and recrystallization at sub-arc pressures and temperatures. Considering the large amount of olivine in the mantle wedge, transport of slab-derived material to magma sources requires processes with minimal interaction with mantle peridotite, such as intensely channelized fluid flow or ascent of mélange diapirs, and limited porous fluid flow. [ABSTRACT FROM AUTHOR]

The crustally derived Tungsten Plutonic Suite (TPS) in the northern Canadian Cordillera is responsible for several of the world's most important tungsten (W) resources, but the actual source rocks to these exceptionally metallogenic magmas have never been identified. Detrital zircon studies have improved our knowledge of exposed supracrustal packages in the region, such that a U-Pb study of inherited zircon cores in the TPS provides an opportunity to determine the age and provenance of the melt source to these magmas. The TPS is dominated by Neoarchean to Paleoproterozoic inherited zircons that are typical of a northwest Laurentian "cratonic" detrital zircon signature (e.g., 2.8-1.8 Ga). Cross-correlation statistical analysis of detrital zircon populations combined with whole-rock neodymium isotopic compositions indicate that mid- to late Cambrian sedimentary rocks in the Selwyn Basin are the most likely melt source for the TPS magmas. Despite the presence of prospective intrusions across the Selwyn Basin, world-class W metallogeny is limited to the narrow belt of TPS plutons in the eastern Selwyn Basin near the ancient continental margin, possibly due to depositional or structural controls on the source strata. Today, the early Phanerozoic melt source to the TPS must be present at depths of at least 15-17 km and is notably younger than suggested by current geophysical interpretations for the middle crust, requiring a reconsideration of the crustal architecture in the northern Canadian Cordillera. [ABSTRACT FROM AUTHOR]

Previous studies of Pinatubo have shown that basaltic magma was injected into what was thought to be a homogeneous dacitic magma reservoir just before the 1991 eruptions. Mingling of the basalt and dacite resulted in a volatile-charged hybrid andesitic magma that ascended through the overlying dacite reservoir, triggering initial andesitic eruptions and the climactic eruption of dacite a few days later. Using mineral and whole-rock chemistry and isotopic data, we show that the dacitic magma was not homogeneous, but was instead heterogenous, produced from heterogeneous dacitic magma, which is approximated by at least two distinct silicic end-member magmas. Our data show that these silicic magmas were not produced by fractional crystallization of basaltic magma, such as that which formed the basalt enclaves of the 1991 and Buag period basalts (~ 1.0–0.5 ka). Instead, we argue that the 1991 dacite magmas were produced independently but simultaneously by the melting of heterogeneous crustal materials. Based on these results, we propose the following sequence of events. First, basaltic magma distinct from that of the Buag period underplated and heated the crust to form silicic melt pockets of various compositions in a crustal mush zone. During the period between 0.5 ka and 1991, these silicic melts separated from the crustal mush zone and accumulated in the crust, forming the 1991 dacitic magma reservoir. Finally, during the climactic phase of the 1991 eruption, heterogeneous dacitic pumices were erupted, having a composition range that is representative of their variable crustal origins. [ABSTRACT FROM AUTHOR]

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The injection of mafic magma into a hydrous felsic magma chamber is a potential trigger mechanism for bimodal explosive volcanism. As H 2 O is the most abundant volatile component in magmas, the interaction and the degassing behavior of mildly peralkaline hydrous rhyolitic melt in contact with hydrous basaltic melt were investigated by decompression experiments. Preparatory hydration experiments and bimodal magma decompression experiments, as well as reference experiments, were carried out in an internally heated argon pressure vessel. Pre-hydrated rhyolite and basalt cylinders were perfectly contacted together in a precious-metal capsule, heated to 1348 K at 210 MPa, and thermally equilibrated for 10 min. The initial sample properties were determined by a bimodal reference experiment, quenched immediately after equilibration. To simulate the magma ascent, three bimodal samples and a decompression experiment with two contacted rhyolite cylinders for testing the experimental setup were decompressed with 0.17 or 1.7 MPa s -1 to the final pressure of 100 MPa and then quenched. All decompression experiments resulted in vesiculated samples. The H 2 O vesicles observed in the decompressed sample of the monomodal rhyolite–rhyolite reference experiment are homogeneously distributed throughout the sample. The former interface between the contacted glass cylinders is invisible after decompression and quench. This reference experiment proves that the two-cylinder design does not influence the degassing behavior of the hydrous melt, e.g., an increased formation of vesicles at possible nucleation sites at the contact plane of the cylinders. The undecompressed bimodal rhyolite–basalt sample shows crystal-free rhyolitic glass, whereas 3 µ m sized idiomorphic magnetite crystals coexist with glass in the basaltic part of the sample. Within the 10 min run time, a ∼ 300 µ m wide hybrid composition zone developed between the hydrous rhyolitic and basaltic endmembers, caused by diffusion-induced mixing processes. Decompression and quenching of the bimodal melts resulted in vesiculated glass samples. A ∼ 100 µ m wide zone of alkali-depleted rhyolitic glass as part of the ∼ 300–560 µ m wide hybrid zone is covered with an enhanced number of H 2 O vesicles compared to the pristine rhyolitic and basaltic glass volumes. We suggest that this enhanced vesiculated zone forms by a rapid diffusional loss of alkalis from the mildly peralkaline rhyolitic melt into the basaltic melt of the sample. The reduced alkali concentration significantly reduces the H 2 O solubility of the rhyolitic melt. This process enhances the H 2 O supersaturation necessary for vesicle formation during decompression. In summary, the new findings imply that convective magma ascent driven by the injection of hot basaltic magma into a hydrous peralkaline rhyolitic melt reservoir leads to enhanced H 2 O vesicle formation near the melt interface and thus to efficient degassing. This in turn can accelerate buoyancy-driven magma ascent and mingling and mixing processes that induce further degassing and potentially trigger explosive volcanic eruptions. [ABSTRACT FROM AUTHOR]

The compositions of volcanic materials are sensitive to physical conditions in the underlying magmatic system. When basaltic melts are saturated in olivine‐plagioclase‐augite prior to eruption, their compositions can be used to estimate the pressure at which they last equilibrated. We developed PyOPAM, an open‐source tool that runs in Python, and use this refreshed liquid‐barometer to investigate the relationship between final depths of magma storage and magma flux. We first tested PyOPAM using 312 experimental glasses compiled from literature and found that the 1σ uncertainty is 1.13 kbar (±3 km). PyOPAM was then applied to a data set of 13,400 analyses from Iceland, where suspected controls on magma flux are well constrained. Of these, 3807 analyses return robust pressure estimates, constraining final pre‐eruptive magma storage depths for 23 of the 30 Icelandic volcanic systems. Our results indicate that magma storage pressures on Iceland are linked to melt‐flux from the mantle. This finding is consistent with previous models linking storage depths and spreading rates on the global mid‐ocean ridge system. In addition, we provide clear evidence that the magma flux, rather than spreading rate alone, is the key control on the distribution of melt at spreading centers. Increased melt flux is associated with shoaling of pre‐eruptive storage depths, indicating that mantle melt fluxes dictate the long‐term stabilization of extensive magmatic storage regions at depths shallower than 10 km. Quantitative relationships between mantle melt flux and storage depths can be used to test computational models of transcrustal magmatic systems. Plain Language Summary: An important part of monitoring volcanoes is understanding where magma is stored before an eruption. Some individual volcanic systems have been rigorously studied and their plumbing systems are well understood. However, the overall physical controls on the depths of magma storage under volcanic systems are not yet resolved. In a free python script (PyOPAM), we refreshed and streamlined a basaltic liquid barometer, that allows us to estimate the final depth of storage for a basaltic magma, ±1.13 kbar. We applied this tool to basaltic samples from Iceland. Of the original 13,400 analyses entered into PyOPAM, 3800 returned reliable estimates. We find that there is a relationship between the amount of magma being produced and moving through an area, and the final depth of storage for basaltic magma before eruption. With increasing magma production, magma storage depths decrease and shift into the shallow crust. When magma production is low, basaltic magma is stored in the lower crust or mantle. This pattern is modified by the temperature of the crust, as cold crust prevents shallow storage of basaltic magma. These findings can be applied to other basaltic volcanoes and magma systems throughout the world. Key Points: We created pyOPAM, a python script for applying the OPAM barometer to basaltic liquidsUsing statistical filters we constrained the uncertainty to 1 σ of this barometer to 1.13 kbarWe applied pyOPAM to Icelandic samples and find that final depths of basaltic magma storage is controlled by magma flux [ABSTRACT FROM AUTHOR]