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We have determined the solubility of sulfur (S) as sulfide (S2–) for 13 different natural melt compositions at temperatures of 1473–1773 K under controlled conditions of oxygen and sulfur fugacities (fO2 and fS2, respectively). The S and major element contents of the quenched glasses were determined by electron microprobe. The sulfide capacity parameter (CS2–) was used to express S2– solubility as a function of the oxygen and sulfur fugacities according to the equation: logCS2-=logSmeltwt%+0.5logfO2fS2. Sulfide capacities of silicate melts were found to increase with temperature and the FeO content of the melt. We combined our sulfide data at 1473–1773 K with (O’Neill and Mavrogenes, J Petrol 43:1049–1087, 2002) results at 1673 K, and obtained by stepwise linear regression the following equation for sulfide capacity logCS2-=0.225+25237XFeO+5214XCaO+12705XMnO+19829XK2O-1109XSi0.5O-8879/T. XMO is the mole fraction of the oxide of M on a single-oxygen basis, and T is in Kelvin. The sulfide capacity equation was combined with sulfate capacity (CS6+) data for similar compositions and at the same temperatures (Boulliung and Wood, Geochim Cosmochim Acta 336:150–164, 2022), to estimate the S redox state (S6+/S2– ratio) as a function of melt composition, temperature and oxygen fugacity. Results obtained are in good agreement with earlier measurements of S6+/S2– for basaltic and andesitic compositions. We observe a significant increase, however, relative to FMQ of the oxygen fugacity of the S2– to S6+ transition as temperature is lowered from 1773 to 1473 K. We used our results to simulate sulfur-degassing paths for basaltic compositions under various redox conditions (FMQ –2 log fO2 units to FMQ + 2). The calculations indicate that, given an initial concentration of 0.12 wt% S in an ascending melt at 250 MPa, most of the S (> 80%) will be degassed before the magma reaches 100 MPa pressure.

Silicate-sulfide liquid immiscibility in mantle-derived magmas has important control on the budget of siderophile and chalcophile metals, and is considered to be instrumental in the origin orthomagmatic sulfide deposits. Data on primitive sulfide melts in natural samples, even those representing most voluminous magmatism in oceanic rifts, are very scarce due to the small size and poor preservation of incipient sulfide melt globules. Here we present the first detailed report of the crystallized sulfides melts in the oceanic picrites of the (presumably) Cretaceous age Kamchatsky Mys ophiolite complex in Eastern Kamchatka (Far East Russia). Sulfide melts are present in three forms; (1) as inclusions in olivine (87.1-89.6 mol% Fo), (2) interstitial to the groundmass minerals (clinopyroxene, plagioclase, and Ti-magnetite) of studied picrites, and (3) as daughter phases in silicate melt inclusions hosted by olivine and Cr-spinel phenocrysts. The sulfide melt inclusions in olivine and the groundmass of studied rocks are composed of several sulfide phases that correspond to the monosulfide (Fe-Ni; Mss) and intermediate (Fe-Cu-Ni; Iss) solid solutions. Several <0.5 µm Pd-Sn, Pt-Ag, and Au-Ag phases are recorded within the matrix sulfides, commonly along phase boundaries and fractures. Major elements (S, Fe, Cu, Ni, Co), platinum group elements (PGE), and gold analyzed in the homogenized olivine-hosted sulfide melt inclusions, and phases identified in the matrix sulfides record the range of magmatic sulfide compositions. The most primitive sulfide liquids are notably enriched in Ni and Cu [(Ni+Cu)/Fe, at% > 0.5], continuously evolve with crystallization of (e.g., increasing Cu/Ni and Au/PGE) and demonstrate metal fractionation between Mss and Iss. Although the compositional systematics found in this study are consistent with those previously recorded, the compositions of individual sulfide phases are strongly affected by the noble metal (PGE, Au) \"nuggets\" that exsolve at subsolidus temperatures and form during serpentinization of the rocks. We conclude that the budget of noble metals in the studied picrites is controlled by sulfides, but the abundances of Pt and Au are influenced by mobility in post-magmatic alteration. Our data can be also used for modeling sulfide saturation at crustal pressures and understanding behavior of the noble metals in primitive oceanic magmas.

This paper introduces Petrolog3, software for modeling (1) fractional and equilibrium crystallization, (2) reverse fractional crystallization at variable pressure, melt oxidation state and melt H2O contents, and (3) postentrapment reequilibration of melt inclusions in olivine. Petrolog3 offers an algorithm that allows calculations with a potentially unlimited number of (1) mineral‐melt equilibrium models for major and trace elements and (2) models describing melt physical parameters such as density and viscosity, melt oxidation state, and solubility of fluid components in silicate melts. The current version of the software incorporates 46 mineral‐melt equilibrium models for 8 minerals; 3 models describing distribution of trace elements between minerals and melt; 4 models of melt oxidation state; 1 model for H2O solubility in silicate melts; and 4 models describing melt density and viscosity. The idea behind the program is to provide the community of igneous petrologists and geochemists with a user‐friendly interface for using any combinations of available mineral‐melt equilibrium models for computer simulation of the crystallization process. Key Points New algorithm for crystallization modeling User friendly software interface Ability to compare available models

Shallow magma chambers either erupt as volcanoes or solidify as intrusive magma bodies. These magma bodies are traditionally considered to be long-lived and dominated by melt. Cashman et al. review the evidence that shallow magma chambers are actually assembled quickly from much larger, crystal-rich transcrustal magmatic systems. This paradigm helps explain many geophysical and geochemical features of volcanic systems. It also presents challenges for understanding the evolution of magma and provides insight into how and why volcanoes erupt. Science , this issue p. eaag3055 Shallow magma chambers are ephemeral expressions of larger transcrustal magmatic systems. Volcanoes are an expression of their underlying magmatic systems. Over the past three decades, the classical focus on upper crustal magma chambers has expanded to consider magmatic processes throughout the crust. A transcrustal perspective must balance slow (plate tectonic) rates of melt generation and segregation in the lower crust with new evidence for rapid melt accumulation in the upper crust before many volcanic eruptions. Reconciling these observations is engendering active debate about the physical state, spatial distribution, and longevity of melt in the crust. Here we review evidence for transcrustal magmatic systems and highlight physical processes that might affect the growth and stability of melt-rich layers, focusing particularly on conditions that cause them to destabilize, ascend, and accumulate in voluminous but ephemeral shallow magma chambers.

A thermodynamic model for estimating the saturation conditions of H 2 O–CO 2 mixed fluids in multicomponent silicate liquids is described. The model extends the capabilities of rhyolite-MELTS (Gualda et al. in J Petrol 53:875–890, 2012a ) and augments the water saturation model in MELTS (Ghiorso and Sack in Contrib Mineral Petrol 119:197–212, 1995 ). The model is internally consistent with the fluid-phase thermodynamic model of Duan and Zhang (Geochim Cosmochim Acta 70:2311–2324, 2006 ). It may be used independently of rhyolite-MELTS to estimate intensive variables and fluid saturation conditions from glass inclusions trapped in phenocrysts. The model is calibrated from published experimental data on water and carbon dioxide solubility, and mixed fluid saturation in silicate liquids. The model is constructed on the assumption that water dissolves to form a hydroxyl melt species, and that carbon dioxide both a molecular species and a carbonate ion, the latter complexed with calcium. Excess enthalpy interaction terms in part compensate for these simplistic assumptions regarding speciation. The model is restricted to natural composition liquids over the pressure range 0–3 GPa. One characteristic of the model is that fluid saturation isobars at pressures greater than ~100 MPa always display a maximum in melt CO 2 at nonzero H 2 O melt concentrations, regardless of bulk composition. This feature is universal and can be attributed to the dominance of hydroxyl speciation at low water concentrations. The model is applied to four examples. The first involves estimation of pressures from H 2 O–CO 2 -bearing glass inclusions found in quartz phenocrysts of the Bishop Tuff. The second illustrates H 2 O and CO 2 partitioning between melt and fluid during fluid-saturated equilibrium and fractional crystallization of MORB. The third example demonstrates that the position of the quartz–feldspar cotectic surface is insensitive to melt CO 2 contents, which facilitates geobarometry using phase equilibria. The final example shows the effect of H 2 O and CO 2 on the crystallization paths of a high-silica rhyolite composition representative of the late-erupted Bishop Tuff. Software that implements the model is available at ofm-research.org, and the model is incorporated into the latest version (1.1+) of rhyolite-MELTS.

Glide-snow avalanches release due to a loss of friction at the snow–ground interface, which can result in large avalanches that endanger infrastructure in alpine regions. The underlying processes are still relatively poorly understood, in part due to the limited data available on glide processes. Here, we introduce a pixel-based algorithm to detect glide cracks in time-lapse photographs under changing illumination and shadow conditions. The algorithm was applied to 14 years of time-lapse images at Dorfberg (Davos, Switzerland). We analysed 947 glide-snow events at a high-spatial (0.5 m) and temporal (2–15 min) resolution. Avalanche activity and glide-crack opening dynamics were investigated across timescales ranging from seasonally to hourly. Events were separated into surface (meltwater percolation) and interface events (no meltwater percolation). The results show that glide activity is highly variable between and within seasons. Most avalanches released without crack formation or within 24 h after crack opening, and release was favoured in the afternoon hours. Glide rates often showed a stick–slip behaviour. The acceleration of glide rates and non-constant increases in glide crack aspect ratio were indicators for avalanche release. This comprehensive dataset provides the basis for further investigations into glide-snow avalanche drivers.

By considering the rotationality of shear flow, we distinguish between tube segments created by reptation before the inception of shear flow and those created during flow. Tube segments created before inception of shear flow experience both stretch and orientation, while tube segments created after inception of flow are not stretched, but are only aligned in the flow direction. Based on this idea, the Rotation Zero Stretch (RZS) model allows for a quantitative description of the start-up of shear flow and stress relaxation after step-shear strain experiments, in agreement with data of polystyrene long/short blends and corresponding polystyrene 3-arm star polymers investigated by Liu et al. (Polymer 2023, 281:126125), as well as the shear viscosity data of poly(propylene carbonate) melts reported by Yang et al. (Nihon Reoroji Gakkaishi 2022, 50:127–135). In the limit of steady-state shear flow, the RZS model converges to the Doi-Edwards IA model, which quantitatively describes the steady-state shear viscosity of linear polymer melts and long/short blends. The assumption of “non-stretching” of tube segments created during rotational flow is therefore in agreement with the available experimental evidence. Three-arm star polymers behave in a similar way as corresponding blends of long and short polymers confirming the solution effect of the short arm in asymmetric stars. The analysis of step-shear strain experiments reveals that stress relaxation is at first dominated by stretch relaxation, followed at times larger than the Rouse stretch relaxation time by relaxation of orientation as described by the damping function of the Doi-Edwards IA model. The RZS model does not require any nonlinear-viscoelastic parameter, but relies solely on the linear-viscoelastic relaxation modulus and the Rouse stretch relaxation time. Graphical Abstract

The extent to which sulfur dissolves in silicate melts saturated in an immiscible sulfide phase is a fundamental question in igneous petrology and plays a primary role in the generation of magmatic ore deposits, volcanic degassing, and planetary differentiation. In igneous systems, sulfide melts can be described as FeS-NiS-CuS0.5 solutions with Fe/(Fe+Ni+Cu) significantly less than 1. Despite the presence of Ni and Cu in the sulfide, however, most experimental studies to date have concentrated on the effects of silicate melt composition on sulfur solubility and have used essentially pure FeS as the sulfide liquid. We have carried out 49 new experiments at pressures of 1.5-24 GPa and temperatures of 1400 to 2160 °C to investigate the effects of sulfide composition on sulfur solubility as well as extending the pressure and temperature ranges of the available data on sulfide saturation. We find that in the compositional range of most igneous sulfide melts [Fe/(Fe+Ni+Cu) > 0.6] sulfur solubility decreases linearly with Fe content such that at Fe/(Fe+Ni+Cu) of 0.6 the sulfur content at saturation is 0.6 times the value at pure FeS saturation. At lower values of Fe/(Fe+Ni+Cu), however, deviations from this ideal solution relationship need to be taken into consideration. We have treated these non-idealities by assuming that FeS-NiS-CuS0.5 liquids approximate ternary regular solutions.We have fitted our data, together with data from the literature (392 in total), to equations incorporating the effects of silicate melt composition, sulfide liquid composition, and pressure on the solubility of sulfur at sulfide saturation ([S]SCSS). The temperature dependence of [S]SCSS was assumed either to be an unknown or was taken from 1 bar thermodynamic data. The most important best-fit silicate melt compositional term reflects the strongly positive dependence of [S]SCSS on the FeO content of the silicate melt. The best-fit value of this parameter is essentially independent of our assumptions about temperature dependence of [S]SCSS or the solution properties of the sulfide. All natural compositions considered here exhibit positive dependences of [S]SCSS on temperature and negative dependences on pressure, in accord with previous studies using smaller data sets.

Magma reservoirs play a key role in controlling numerous processes in planetary evolution, including igneous differentiation and degassing, crustal construction, and volcanism. For decades, scientists have tried to understand what happens in these reservoirs, using an array of techniques such as field mapping/petrology/geochemistry/geochronology on plutonic and volcanic lithologies, geophysical imaging of active magmatic provinces, and numerical/experimental modeling. This review paper tries to follow this multi-disciplinary framework while discussing past and present ideas. We specifically focus on recent claims that magma columns within the Earth's crust are mostly kept at high crystallinity (\"mush zones\"), and that the dynamics within those mush columns, albeit modulated by external factors (e.g., regional stress field, rheology of the crust, pre-existing tectonic structure), play an important role in controlling how magmas evolve, degas, and ultimately erupt. More specifically, we consider how the chemical and dynamical evolution of magma in dominantly mushy reservoirs provides a framework to understand: (1) the origin of petrological gradients within deposits from large volcanic eruptions (\"ignimbrites\"); (2) the link between volcanic and plutonic lithologies; (3) chemical fractionation of magmas within the upper layers of our planet, including compositional gaps noticed a century ago in volcanic series (4) volatile migration and storage within mush columns; and (5) the occurrence of petrological cycles associated with caldera-forming events in long-lived magmatic provinces. The recent advances in understanding the inner workings of silicic magmatism are paving the way to exciting future discoveries, which, we argue, will come from interdisciplinary studies involving more quantitative approaches to study the crust-reservoir thermo-mechanical coupling as well as the kinetics that govern these open systems.