High Sulfur in Primitive Arc Magmas, Its Origin and Implications

Sulfur contents in 98.5% of melt inclusions (MI) from calc-alkaline subduction basalts do not exceed 4000 ppm, whereas experimentally established limits of sulfur solubility in basaltic melts with high fO2 (characteristic of subduction zones, e.g., QFM + 2) surpass 14,000 ppm. Here we show that primitive (Mg# 62-64) subduction melts may contain high sulfur, approaching the experimental limit of sulfur solubility. Up to 11,700 ppm S was measured in olivine-hosted MI from primitive arc basalt from the 1941 eruption of the Tolbachik volcano, Kamchatka. These MI often contain magmatic sulfide globules (occasionally enriched in Cu, Ni, and platinum-group elements) and anhydrite enclosed within a brown, oxidized glass. We conclude that the ubiquitous low sulfur contents in MI may originate either from insufficient availability of sulfur in the magma generation zone or early magma degassing prior to inclusion entrapment. Our findings extend the measured range of sulfur concentrations in primitive calc-alkaline basaltic melts and demonstrate that no fundamental limit of 4000 ppm S exists for relatively oxidized subduction basalts, where the maximum sulfur content may approach the solubility limit determined by crystallization of magmatic anhydrite.

MagmaFOAM-1.0: a modular framework for the simulation of magmatic systems

Numerical simulations of volcanic processes play a fundamental role in understanding the dynamics of magma storage, ascent and eruption. The recent extraordinary progress in computer performance and improvements in numerical modeling techniques allow simulating multiphase systems in mechanical and thermodynamical disequilibrium. Nonetheless, the growing complexity of these simulations requires the development of flexible computational tools that can easily switch between sub-models and solution techniques. In this work we present MagmaFOAM, a library based on the open source computational fluid dynamics software OpenFOAM, that incorporates models for solving the dynamics of multiphase, multicomponent magmatic systems. Retaining the modular structure of OpenFOAM, MagmaFOAM allows run-time selection of the solution technique depending on the physics of the specific process, and sets a solid framework for in-house and community model development, testing and comparison. MagmaFOAM models thermo-mechanical non-equilibrium phase coupling and phase change, and implements state-of-the-art multiple volatile saturation models and constitutive equations with composition-dependent and space-time local computation of thermodynamic and transport properties. Code testing is performed using different multiphase modeling approches for processes relevant to magmatic systems: Rayleigh-Taylor instability, for buyoancy-driven magmatic processes; multiphase shock tube simulations, propedeutical to conduit dynamics studies; bubble growth and breakage in basaltic melts. Benchmark simulations illustrate the capabilities and potential of MagmaFOAM to account for the variety of non-linear physical and thermodynamical processes characterizing the dynamics of volcanic systems.

Supplemental Material: Mafic-ultramafic intrusion formed by multi-stage evolution of hydrous basaltic melts

Table S1: Electron microprobe analyses of spinel; Table S2: Electron microprobe analyses of olivine; Table S3: Electron microprobe analyses of clinopyroxene; Table S4: Electron microprobe analyses of orthopyroxene; Table S5: Electron microprobe analyses of plagioclase; Table S6: Electron microprobe analyses of amphibole; Table S7: EC-AFC modeling results for the contamination of average lower crust.

Supplemental Material: Mafic-ultramafic intrusion formed by multi-stage evolution of hydrous basaltic melts

Table S1: Electron microprobe analyses of spinel; Table S2: Electron microprobe analyses of olivine; Table S3: Electron microprobe analyses of clinopyroxene; Table S4: Electron microprobe analyses of orthopyroxene; Table S5: Electron microprobe analyses of plagioclase; Table S6: Electron microprobe analyses of amphibole; Table S7: EC-AFC modeling results for the contamination of average lower crust.

Modeling of Olivine and Clinopyroxene Fractionation in Intracontinental Alkaline Basalts: A Case Study from the Carpathian-Pannonian Region

Besides mantle peridotites primary basaltic melts are the best tool to investigate upper mantle petrology and geochemistry. However, de facto primitive melts are hard to found, as basaltic melts usually go through a fractionation process during their ascent towards the surface. Most primary melt calculators are based on the major or trace element compositions of olivine-phyric ocean island basalts and peridotites and are less accurate if clinopyroxene fractionation occurred. In this chapter a new fractionation modeling method of alkaline basalts will be introduced, which has been published earlier only in Hungarian. Olivine ± clinopyroxene fractionation of four basaltic volcanoes have been modeled from different Miocene-Quaternary volcanic fields from the Carpathian-Pannonian Region (Stiavnica (Selmec) VF, Novohrad-Gemer (Nógrád-Gömör) VF, Perşani Mts. (Persányi Mts.) VF and from the Lucaret-Sanoviţa (Lukácskő-Sziklás) volcano.

The Rare Trachyandesitic Lavas at Mount Etna: A Case Study to Investigate Eruptive Process and Propose a New Interpretation for Magma Genesis

The growth of Mount Etna volcano reflects the superimposition of various eruptive centers, the most voluminous of which is the Ellittico, whose stratigraphic sequence is well exposed on the steep walls of Valle del Bove. The uppermost levels of the sequence have been sampled and investigated through a new set of geochemical data on mineral phases and bulk rock. Sampled rocks display a marked bimodality with aphyric banded trachyandesites, which are some of the most evolved and rare products of the entire Etnean succession (SiO2 58–60 wt.%), intercalated in plagioclase rich porphyritic mugearites (SiO2 49–50 wt.%, P.I. 35–40). In this paper, we provide a detailed textural, mineralogical, and chemical characterization of these products, providing a new interpretative model for their genesis and significance in the context of the Etnean system. Our approach discusses, in a critical way, the “classic” fractional crystallization model of magmas, not supported by field evidence, and proposes a novel hypothesis in which the aphyric-banded trachyandesites represent be the primary products of a gas-induced partial melting of hypabyssal sills and dykes. This hypothesis represents a step towards a comprehensive description of igneous systems that takes into account not exclusively the evolution of basaltic melts, but also the role of volatile contributions in governing volcanic behavior.

Evolution of intraplate alkaline to tholeiitic basalts via interaction between carbonated melt and lithospheric mantle

Intraplate basaltic volcanism commonly exhibits wide compositional ranges from silica-undersaturated alkaline basalts to silica-saturated tholeiitic basalts. Possible mechanisms for the compositional transition involve variable degrees of partial melting of a same source, decompression melting at different mantle depths (so-called “lid effect”), and melt-peridotite interaction. To discriminate between these mechanisms, here we investigated major-trace elemental and Sr-Nd-Mg-Zn isotopic compositions of a suite of intraplate alkaline and tholeiitic basalts from the Datong volcanic field in eastern China. Specifically, we employed Mg and Zn isotope systematics to assess whether the silica-undersaturated melts originated from a carbonated mantle source. The alkaline basalts have young HIMU-like Sr and Nd isotopic compositions, lower δ26Mg (-0.42‰ to -0.38‰) and higher δ66Zn (0.40‰ to 0.46‰) values relative to the mantle. These characteristics were attributable to an asthenospheric mantle source hybridized by carbonated melts derived from the stagnant Pacific slab in the mantle transition zone. From alkaline to tholeiitic basalts, δ26Mg gradually increases from -0.42‰ to -0.28‰ and δ66Zn decreases from 0.46‰ to 0.28‰ with decreasing alkalinity and incompatible trace element abundances (e.g. Rb, Nb, Th and Zr). The Mg and Zn isotopic variations are significantly beyond the magnitude (<0.1‰) induced by different degrees of fractional crystallization and partial melting of a same mantle source, excluding different degree of partial melting and the “lid effect” as possible mechanisms accounting for the compositional variations in the Datong basalts. There are strong, near-linear correlations of δ26Mg and δ66Zn with 87Sr/86Sr (R2=0.75 − 0.81) and 143Nd/144Nd (R2=0.83 − 0.90), suggesting an additional source for the Datong basalts. This source is characterized by pristine mantle-like δ26Mg and δ66Zn values as well as EM1-like Sr-Nd isotopic ratios, pointing towards a metasomatized subcontinental lithospheric mantle (SCLM). Isotope mixing models show that mingling between alkaline basaltic melts and partial melts from the SCLM imparts all the above correlations, which means that the SCLM must have been partially melted during melt-SCLM reaction. Our results underline that interaction between carbonated silica-undersaturated basaltic melts and the SCLM acts as one of major processes leading to the compositional diversity in intracontinental basaltic volcanism.