J. M. de Moor

TL;DR: In this article, the authors reported new helium and carbon isotope (3 He/ 4 He and δ 13 C) and relative abundance (CO 2 / 3 He) characteristics of a suite of 20 gases and fluids (cold mazuku-like CO 2 vents, bubbling mudpots, hot and cold springs) from 11 different localities in Rungwe Volcanic Province (RVP), southern Tanzania and from 3 additional localities (Oldoinyo Lengai Volcano and Lake Natron).

Abstract: We investigate the relationship between sulfur and oxygen fugacity at Erta Ale and Masaya volcanoes. Oxygen fugacity was assessed utilizing Fe3+/Sigma Fe and major element compositions measured in olivine-hosted melt inclusions and matrix glasses. Erta Ale melts have Fe3+/Sigma Fe of 0.15-0.16, reflecting fO(2) of Delta QFM 0.0 +/- 0.3, which is indistinguishable from fO(2) calculated from CO2/CO ratios in high-temperature gases. Masaya is more oxidized at Delta QFM + 1.7 +/- 0.4, typical of arc settings. Sulfur isotope compositions of gases and scoria at Erta Ale (delta S-34(gas) - 0.5 parts per thousand; delta S-34(scoria) + 0.9 parts per thousand) and Masaya (delta S-34(gas) + 4.8 parts per thousand; delta S-34(scoria) + 7.4 parts per thousand) reflect distinct sulfur sources, as well as isotopic fractionation during degassing (equilibrium and kinetic fractionation effects). Sulfur speciation in melts plays an important role in isotope fractionation during degassing and S6+/Sigma S is 0.67 in Masaya melt inclusions. No change is observed in Fe3+/Sigma Fe or S6+/Sigma S with extent of S degassing at Erta Ale, indicating negligible effect on fO(2), and further suggesting that H2S is the dominant gas species exsolved from the S2--rich melt (i.e., no redistribution of electrons). High SO2/H2S observed in Erta Ale gas emissions is due to gas re-equilibration at low pressure and fixed fO(2). Sulfur budget considerations indicate that the majority of S injected into the systems is emitted as gas, which is therefore representative of the magmatic S isotope composition. The composition of the Masaya gas plume (+4.8 parts per thousand) cannot be explained by fractionation effects but rather reflects recycling of high delta S-34 oxidized sulfur through the subduction zone

TL;DR: In this paper, the authors report on short-term precursory variations in gas emissions related to phreatic blasts at Poas volcano, Costa Rica, as measured with an in situ multiple gas analyzer that was deployed at the edge of the erupting lake.

TL;DR: In the forearc regions of Costa Rica, helium and carbon isotope data reveal that about 20 per cent less carbon is being transported into the deep mantle than previously thought.

TL;DR: In this paper, the authors reported helium isotope ratios (3He/4He) of lavas and tephra of the Rungwe Volcanic Province (RVP) in southern Tanzania.