Dear All,
Our Smith Lecture speaker this week is Adrian Fiege, Department of Earth and Environmental Sciences. He is speaking on "Kinetics of Sulfur Degassing During Decompression of Silicate Melts". Abstract below.
Our Smith Lecture speaker this week is Adrian Fiege, Department of Earth and Environmental Sciences. He is speaking on "Kinetics of Sulfur Degassing During Decompression of Silicate Melts". Abstract below.
Smith Lectures are Friday afternoons from 4:00 to 5:00 pm, in Room 1528 C.C. Little Building. A reception is held following the lecture in 2540 C.C. Little. The events are free and open to the public. A full schedule for the term may be found on our website:
Best regards, -Anne
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Anne Hudon
Academic Student Services
Department of Earth and Environmental Sciences
University of Michigan
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Abstract:
Sulfur (S) is a major volatile in magmatic systems and large amounts of S can be released to the atmosphere during volcanic eruptions as well as passively between two eruptions. Hence, a good knowledge of the S degassing mechanisms in magmatic systems is a pre-requisite to allow one to interpret volcanic gas signatures and, thus, to improve monitoring of active volcanic systems. However, data on S fluid-melt distribution are rare and, until recently, no experimental data on the kinetics of S degassing during decompression of silicate melts were published.
We conducted isothermal decompression experiments with volatile-bearing (H2O-S±Cl) andesitic and basaltic melts at temperatures (T) of 1030 to 1250°C and various oxygen fugacities fO2 (log(fO2/bar) = QFM to QFM+4; QFM: quartz-fayalite-magnetite buffer). In these experiments, pressure (p) was released continuously from ~400 to ~70 MPa at a constant rate of ~0.1 MPa/s. The samples were annealed for tA = 0 to 72 h at final p-T conditions after decompression to allow us to investigate the kinetics of S degassing.
Experiments with andesitic composition conducted under oxidizing conditions (>QFM+3) and at ~1030°C revealed a strong decrease of the S(fluid)/S(melt) ratio with increasing tA (S(fluid) = wt% S in the fluid; S(melt) = wt% S in the melt). The data show that fluid-melt near-equilibrium conditions were achieved shortly after decompression; i.e., within ~5 h. Such a kinetically controlled transient release of large amounts of S from a melt to a fluid phase during fast decompression was not observed at lower fO2 (~QFM+1 to ~QFM+1.5) in andesitic systems and was not detected at all (i.e., independent of fO2) in basaltic systems.
