VESIcal Part II: A critical approach to volatile solubility modelling using an open-source Python3 engine

Accurate models of H2O and CO2 solubility in silicate melts are vital for understanding volcanic plumbing systems. These models are used to estimate the depths of magma storage regions from melt inclusion volatile contents, investigate the role of volatile exsolution as a driver of volcanic eruptions, and track the degassing paths followed by magma ascending to the surface. However, despite the large increase in the number of experimental constraints over the last two decades, many recent studies still utilize the earlier generation of models, which were calibrated on experimental datasets with restricted compositional ranges. This may be because many of the available tools for more recent models require large numbers of input parameters to be hand-typed (e.g., temperature, concentrations of H2O, CO2, and 8--14 oxides), making them difficult to implement on large datasets. Here, we use a new open-source Python3 tool, VESIcal, to critically evaluate the behaviours and sensitivities of different solubility models for a range of melt compositions. Using literature datasets of andesitic-dacitic experimental products and melt inclusions as case studies, we illustrate the importance of evaluating the calibration dataset of each model. Finally, we highlight the limitations of particular data presentation methods such as isobar diagrams, and provide suggestions for alternatives, and best practices regarding the presentation and archiving of data. This review will aid the selection of the most applicable solubility model for different melt compositions, and identifies areas where additional experimental constraints are required

Volatile release from intrusive magma bodies of terrestrial planets

<p>Besides the accretion from the solar nebular and the degassing from magma oceans, the main source of the atmospheres of terrestrial planets is magmatic volatile release from the interior. The atmosphere on early Earth is crucial for the emergence and evolution of life. It´s build-up and composition is largely influenced by magmatic outgassing. This outgassing process includes the well-studied extrusive as well as the often neglected intrusive volatile release. However, it is assumed that the intrusive magma production rates - at least on Earth - are significantly higher compared to extrusive rates, which makes the investigation and quantification of possible volatile exsolution processes even more important.</p> <p>We simulate the crystallization of an intrusive magma body emplaced at different depths within the lithosphere. As the solubility of volatiles like H<sub>2</sub>O and CO<sub>2</sub> increases with pressure, they usually do not exsolve from the melt. However, through the precipitation of nominally dry minerals, the remaining melt is enriched in incompatible elements and volatiles. They accumulate until a saturation level is reached and the volatiles exsolve. The composition of the resulting volatile phase depends on the solubility of the volatile species, the pressure and temperature, the initial composition of the melt, the partition coefficient and the oxygen fugacity. We consider these parameters in our model and benchmark our results with literature values. Additionally, we investigate the likelihood of reactions with the surrounding mantle, to form water-bearing minerals, during the ascent of volatiles. Finally, we quantify the impact of intrusive degassing on the build-up and composition of the atmosphere.</p>

Integrating field, textural, and geochemical monitoring to track eruption triggers and dynamics: a case study from Piton de la Fournaise

The 2014 eruption at Piton de la Fournaise (PdF), La Réunion, which occurred after 41 months of quiescence, began with surprisingly little precursory activity and was one of the smallest so far observed at PdF in terms of duration (less than 2 days) and volume (less than 0.4 × 106 m3). The pyroclastic material was composed of golden basaltic pumice along with fluidal, spiny iridescent and spiny opaque basaltic scoria. Density analyses performed on 200 lapilli reveal that while the spiny opaque clasts are the densest (1600 kg m−3) and most crystalline (55 vol. %), the golden pumices are the least dense (400 kg m−3) and crystalline (8 vol. %). The connectivity data indicate that the fluidal and golden (Hawaiian-like) clasts have more isolated vesicles (up to 40 vol. %) than the spiny (Strombolian-like) clasts (0–5 vol. %). These textural variations are linked to primary pre-eruptive magma storage conditions. The golden and fluidal fragments track the hotter portion of the melt, in contrast to the spiny fragments and lava that mirror the cooler portion of the shallow reservoir. Exponential decay of the magma ascent and output rates through time revealed depressurization of the source during which a stratified storage system was progressively tapped. Increasing syn-eruptive degassing and melt–gas decoupling led to a decrease in the explosive intensity from early fountaining to Strombolian activity. The geochemical results confirm the absence of new input of hot magma into the 2014 reservoir and confirm the emission of a single shallow, differentiated magma source, possibly related to residual magma from the November 2009 eruption. Fast volatile exsolution and crystal–melt separation (second boiling) were triggered by deep pre-eruptive magma transfer and stress field change. Our study highlights the possibility that shallow magma pockets can be quickly reactivated by deep processes without mass or energy (heat) transfer and produce hazardous eruptions with only short-term elusive precursors.

Tracing the chemical evolution of primary pyrochlore from plutonic to volcanic carbonatites: the role of fluorine

Three Angolan carbonatites were selected to evaluate the change in composition of pyrochlores during magmatic evolution: the Tchivira carbonatites occur in a plutonic complex, the Bonga carbonatites represent hypabyssal carbonatites and the Catanda carbonatites are volcanic in origin. In Tchivira pyrochlore, zoning is poorly developed; fluorine is dominant at the Y site; chemical zoning may arise as a result of substitutions for Nb in the B site; and the rare earth element (REE), U, Th and large-ion lithophile element (LILE) contents are very low. Pyrochlores from Bonga show oscillatory zonation; the F and Na contents are lower than those in the pyrochlores from Tchivira; and as substitution of Na at the A site increases, the Th, U, REE contents and inferred vacancies also increase. Pyrochlores from Catanda display complex textures. They generally have a rounded corroded core, which is mantled by two or three later generations. The core composition is similar to the Bonga pyrochlores. The rims are enriched in Zr, Ta, Th, Ce and U, but depleted in F and Na. In pyrochlores from the Angolan carbonatites, the F and Na contents decrease from plutonic to volcanic settings and there is enrichment of Th, U and REE in the A site and Ta and Zr in the B site. Zoning may be explained by changes in the activity of F, due to the crystallization of fluorite or apatite in the plutonic and hypabyssal carbonatites, or to volatile exsolution in the volcanic carbonatites.