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| Titel |
New experimental data on the antigorite dehydration in silica enriched serpentinite |
| VerfasserIn |
José Alberto Padrón-Navarta, Jörg Hermann, Carlos J. Garrido, Vicente López Sánchez-Vizcaíno, María Teresa Gómez-Pugnaire |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250042449
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| Zusammenfassung |
| There is a growing body of evidences for complex interaction between highly reactive fluids
and ultramafic lithologies. Silica metasomatism, for example, can occur at the basement of
slow-spreading mid-ocean ridges and during prograde metamorphism of chaotically
intermixing in mélange zones of ultramafic rocks, metasediments and metabasites in
subduction settings. The resulting assemblage diagnostic of metaperidotites that experienced
silica metasomatism are talc-schist and talc-bearing serpentinite. These lithologies may
hence be common in subduction settings and will undergo different dehydration
reactions. Antigorite and talc will react at lower temperature than the terminal antigorite
dehydration. Although this reaction is not expected to be as important in the transfer of
water to mantle depth as the breakdown of antigorite, it represents nevertheless
a dehydration event in subduction zones that has not been considered so far. We
anticipate that this reaction might be particularly important for the fore-arc mantle
wedge.
Piston cylinder experiments were performed to constrain the pressure and temperature
conditions for two high-pressure antigorite dehydration reactions found in silica-enriched
serpentinites from Cerro del Almirez (Nevado–Filábride Complex, Betic Cordillera, southern
Spain) [1]. At 630–660ºC and pressures greater than 1.6 GPa, antigorite first reacts
with talc to form orthopyroxene ± chlorite + fluid. We show that orthopyroxene +
antigorite is restricted to high-pressure metamorphism of silica-enriched serpentinite.
This uncommon assemblage is helpful in constraining metamorphic conditions in
cold subduction environments, where antigorite serpentinites have no diagnostic
assemblages over a large range in PT space [2,3]. The second dehydration reaction leads
to the breakdown of antigorite to olivine + orthopyroxene + chlorite + fluid. The
maximum stability of antigorite is found at 680ºC at 1.9 GPa, which also corresponds to
the maximum pressure limit for tremolite coexisting with olivine + orthopyroxene
[4].
[1] Trommsdorff, López Sánchez-Vizcaíno, Gómez-Pugnaire, and Müntener (1998),
Contrib Mineral Petr 132 139-148.
[2] Hermann, Müntener, and Scambelluri, (2000) Tectonophysics 327, 225-238.
[3] Scambelluri, Müntener, Hermann, Piccardo, and Trommsdorff, Geology 23,
459-462.
[4] Padrón-Navarta, Hermann, Garrido, López Sánchez-Vizcaíno, and Gómez-Pugnaire
(2010), Contrib Mineral Petr 159, 25-42. |
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