Zoltán Zajacz

Origin of sulfide inclusions in cumulate xenoliths from Nograd-Gomor Volcanic Field, Pannonian Basin (north Hungary/south Slovakia)

Abstract We provide new information about the evolution of the lithosphere beneath the Nograd–Gomor Volcanic Field (NGVF, northern Pannonian Basin) based on sulfide inclusions in cumulate-origin ultramafic xenoliths. The clinopyroxene-rich cumulate xenoliths, representing the lower crust and upper mantle, underwent metasomatic alteration, which resulted in formation of amphiboles. We have carried out a detailed petrographic observation on sulfide inclusions using reflected light microscope and analyzed numerous back-scattered electron images of the most typical sulfide blebs. Based on the petrographic study, only rounded, elongated or negative crystal-shaped single inclusions, occurring randomly in clinopyroxene and amphibole and rarely in olivine and spinel, have been selected for detailed electron microprobe analysis. The size of these single inclusions ranges from 3 to 75 μm in diameter. The sulfide blebs consist mostly of pyrrhotite and minor chalcopyrite, pentlandite and cubanite. Pyrrhotite, which is the major phase in all the inclusions, is Ni poor (max 6.1 wt.%). Chalcopyrite is deficient in Cu content (≥28.9 wt.%). Pentlandite and cubanite show regular compositions and were identified only in one xenolith. The bulk compositions of sulfide blebs show a tight compositional range and are rich in Fe compared to those in Type-I peridotite xenoliths from the same volcanic field [Geochim. Cosmochim. Acta 59 (1995) 3917; Falus, Gy., 2000. Geochemical significance of sulfide inclusions of Cr-diopsidic xenoliths of alkaline basalts occurring in the Carpathian–Pannonian Region. MSc thesis, Department of Petrology and Geochemistry, Eotvos University, Budapest]. The sulfide blebs studied likely formed from a sulfide melt coexisting with a silicate melt. The latter melt was the source of host clinopyroxene-rich cumulates. The sulfide blebs (mineralogically pyrrhotite) experienced a high- and low-temperature evolution, producing further sulfide phases (chalcopyrite, pentlandite, cubanite) present in the blebs.

The role of crystallization-driven exsolution on the sulfur mass balance in volcanic arc magmas†

The release of large amounts of sulfur to the stratosphere during explosive eruptions affects the radiative balance in the atmosphere and consequentially impacts climate for up to several years after the event. Providing quantitative estimates for the processes that control the mass balance of sulfur between melt, crystals and vapor bubbles is needed to better understand the potential sulfur yield of individual eruption events and the conditions that favor large sulfur outputs to the atmosphere.The processes that control sulfur partitioning in magmas are (1) exsolution of volatiles (dominantly H2O) during decompression (first boiling) and during isobaric crystallization (second boiling), (2) the crystallization and breakdown of sulfide or sulfate phases in the magma and (3) the transport of sulfur-rich vapor transport (gas influx) from deeper unerupted regions of the magma reservoir. Vapor exsolution and the formation/breakdown of sulfur-rich phases can all be considered as closed system process where mass balance arguments are generally easier to constrain, whereas the contribution of sulfur by vapor transport (open system process) is more difficult to quantify. The ubiquitous “Excess Sulfur”, which refers to the much higher sulfur mass released during eruptions than what can be accounted for by the melt inclusion data (petrologic estimate), reflects the challenges in closing the sulfur mass balance between crystals, melt and vapor before and during a volcanic eruption. In this work, we try to quantify the relative importance of closed and open system processes for silicic arc volcanoes using kinetic models of sulfur partitioning during exsolution. Our calculations show that crystallization-induced exsolution (second boiling) can generate a significant fraction of the “Excess Sulfur” observed in crystal-rich arc magmas. This result does not preclude vapor migration to play an important role in the sulfur mass balance, but rather points out that second boiling (in-situ exsolution) can provide the necessary yield to drive the excess sulfur to the levels observed for these eruptions. In contrast, recharges of magma releasing sulfur-rich bubbles are necessary and most likely the primary contributor to the sulfur mass balance in silicic crystal-poor units. Finally, we apply our model to account for the effect of sulfur partitioning during second boiling and its impact on sulfur released during the Cerro Galan super-eruption in Argentina (2.08 Ma), and show the importance of second boiling in releasing a large amount of sulfur to the atmosphere during the eruption of large crystal-rich ignimbrites.

A Raman calibration for the quantification of SO42– groups dissolved in silicate glasses: Application to natural melt inclusions

Abstract Sulfur is an important volatile element involved in magmatic systems. Its quantification in silicate glasses relies on state-of-the-art techniques such as electronprobe microanalyses (EPMA) or X-ray absorption spectroscopy but is often complicated by the fact that S dissolved in silicate glasses can adopt several oxidation states (S6+ for sulfates or S2− for sulfides). In the present work, we use micro-Raman spectroscopy on a series of silicate glasses to quantify the S content. The database is constituted by 47 silicate glasses of various compositions (natural and synthetic) with S content ranging from 1179 to 13 180 ppm. Most of the investigated glasses have been synthesized at high pressure and high temperature and under fully oxidizing conditions. The obtained Raman spectra are consistent with these fO2 conditions and only S6+ is present and shows a characteristic peak located at ~1000 cm−1 corresponding to the symmetric stretch of the sulfate molecular group (ν1 SO42−

A new experimental approach to study fluid–rock equilibria at the slab-mantle interface based on the synthetic fluid inclusion technique

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Halogens in Silicic Magmas and Their Hydrothermal Systems

). The intensity of the ν1 SO42−

Determination of fluid/melt partition coefficients by LA-ICPMS analysis of co-existing fluid and silicate melt inclusions : Controls on element partitioning

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The solubility of copper in high-temperature magmatic vapors: A quest for the significance of various chloride and sulfide complexes

peak is linearly correlated to the parts per million of S6+ determined by EPMA. Using subsequent deconvolution of the Raman spectra, we established an equation using the ratio between the areas of the ν1 SO42−

Microanalysis of S, Cl, and Br in fluid inclusions by LA-ICP-MS

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Alkali metals control the release of gold from volatile-rich magmas

peak and the silicate network species (Qn) in the high-frequency region: ppm S6+=34371ASO42−AQn±609.