 |
| Titel |
COS as an agent of sulfurization of the subduction related magmas. |
| VerfasserIn |
Alexander Simakin, Tamara Salova |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047392
|
|
|
|
|
|
| Zusammenfassung |
| Subduction related tholeitic magmas are often generated in the astenosphere at the lower
pressure and higher temperature than andesitic ones. Tholeitic magmas are also drier and
more reduced. Fluids released from subducting slab may be dried passing through
the lower zone of andesitic magmas generation since water is well dissolved in
these magmas. Such dried fluids of the C-O-S composition would represent mainly
CO2 and COS mixture. We show this by means of thermodynamic modeling at
the upper mantle pressure and oxygen fugacities in the range NNO-3/ NNO+0.5.
Presence of CS2 and CO in such fluid may makes it good carrier for PGE in the form
of solvable Ï-complexes. Sulfurization of olivine rich rocks by COS is possible
with orthopyroxene formation in accordance with reaction: Fe2SiO4 + COS = 1/2
Fe2Si2O6 +FeS +CO2. This equilibrium is affected by olivine and Opx compositions. In
thermodynamic calculations we use Mg-rich composition of Opx and olivines observed in
tholeitic cumulates drawn as volcanic xenoliths to the surface. Thus we get high
COS/CO2 ratio (up to 140) in equilibrium with solid pyrrhotite. Required ratio is higher
than calculated equilibrium COS/CO2 ratio in C-O-S system implying stability of
COS component in solid mantle. Sulfurization of the tholeitic melt by COS may
proceed in the zone of astenosphere melting. In this moment PGE fluid load will be
consumed by forming liquid FeS. Proposed scheme explains observed close link
of sulfide mineralization of the magmatic type and the different forms of carbon.
E.g., in sulfide ores of Kamchatka abundant pure CO2 and CH4-rich bubbles in
magmatic Opx were reported (Konnikov and Vasyukova, 2002). It is essential that
at the pressure decrease from 8 to 2 kbar (shallow crustal depth) at fO2 around
NNO fluid composition is shifted to SO2-CO2 mixture. Pressure of ca 7-8 kbar
and fO2 around QFM for sulfide bearing xenoliths from Avacha and Shiveluch
(Kamchatka) volcanoes have been evaluated with novel amphibole (Simakin et al, 2011)
and conventional two-pyroxene mineral sensors. In the similar conditions of COS
stability magmatic sulfide ores of the Central Kamchatka collision zone have been
formed. COS based fluid may be an agent of Ni enrichment of Opx and Ol reported in
(Ishimaru and Arai, 2008). Authors thank financial support from RFBR grants #
09-05-00313.
References.
S. Ishimaru and S. Arai, Contrib Mineral Petrol (2008) 156:119–131. E.G. Konnikov and
O.N. Vasyukova, Geology of Ore Deposits (2007) 49: 227–237. A.G. Simakin et al.,
Petrology (2011) in press. |
|
|
|
|
|
|