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| Titel |
The role of Iron on the dissolution of Sulfur in hydrous silicate melts |
| VerfasserIn |
K. Klimm, S. C. Kohn, R. E. Botcharnikov |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068495
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| Zusammenfassung |
| It is well established that the sulfur solubility in silicate melts is a function of fO2 and melt
compositions [1]. At high fO2, S6+ is dominant and more soluble in natural silicate
melts than S2-, which is dominant at low fO2. Primitive melt compositions such
as basalt can contain an order of magnitude more sulfur than more evolved melt
compositions such as rhyolite. The compositional control on the sulfur solubility is yet not
fully understood but a positive correlation with FeO has often been observed. Thus,
determining the S2-- and S6+-speciesincorporated in the silicate glass structure is
crucial to unravel the sulfur dissolution mechanism in silicate melts. Together with
solubility measurements such information is essential to quantify the sulfide and
sulfate capacity of silicate melts and to understand the sulfur flux in subduction
zones.
Here we present Raman and XANES measurements on experimentally equilibrated
sulfur-bearing, hydrous silicate glasses, including soda-lime (SLG), K2Si4O9 (KSG), albite
and trondhjemite (TROND) compositions. A series of SLG and KSG glasses, doped with
small quantities of Fe, were also studied in order to determine the effect of Fe/S on the S
solubility. The experiments were performed in internally heated and cold seal pressure
vessels at 200 MPa, 1000 and 850 Ë C and fO2 ranging from logfO2 = QFM-2.4 to
QFM+4.
The systematic correlation of features in Raman and XANES spectra allows the
identification of at least four different S-species in the glasses depending on fO2 and Fe/S of
the system. In Fe-free melts S is dissolved as SH-, H2S and/or SO42- depending on the
prevailing fO2. S2- is more soluble than S6+.The total sulfur solubility depends on the
degree of polymerisation of the melt and increases with increasing NBO/T. This correlation
is much more pronounced for SH- and H2S than for SO42-. Adding Fe results
in the formation of Fe-S-complexes at the expense of SH- and H2S, which are
still observed up to Fe/S ~ 2.6. The S6+/S2- equilibrium in Fe-free systems is at
~1.5 log units lower fO2 than observed for Fe-rich basaltic and andesitic systems
[2,3].
This may have consequences for the S-cycle in subduction zones as Fe-poor slab-derived
liquids are able to carry S6+ which may act as an oxidising agent in the mantle wedge by
successively oxidising Fe2+ to Fe3+.
References:
[1] Carroll & Rutherford (1985) Am Mineral 73, 845-849.
[2] Jugo et al. (2010) GCA 74, 5926-5938.
[3] Botcharnikov et al. (2011) Nature Geo 4, 112-115. |
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