An experimental investigation of antigorite dehydration in natural silica-enriched serpentinite |
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Authors: | José Alberto Padrón-Navarta Jörg Hermann Carlos J Garrido Vicente López Sánchez-Vizcaíno María Teresa Gómez-Pugnaire |
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Institution: | 1. Departamento de Mineralogía y Petrología, Facultad de Ciencias, Universidad de Granada, Avda Fuentenueva s/n, 18002, Granada, Spain 2. Research School of Earth Sciences, The Australian National University, Canberra, 0200, ACT, Australia 3. Instituto Andaluz de Ciencias de la Tierra (IACT), CSIC & UGR, 18002, Granada, Spain 4. Departamento de Geología, Escuela Politécnica Superior, Universidad de Jaén, Alfonso X El Sabio 28, 23700, Linares, Spain 5. Departamento de Mineralogía y Petrología, Facultad de Ciencias, Instituto Andaluz de Ciencias de la Tierra, Universidad de Granada - CSIC, 18002, Granada, Spain
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Abstract: | 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). At 630–660°C 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 pressure and temperature range. The second dehydration reaction leads to the breakdown
of antigorite to olivine + orthopyroxene + chlorite + fluid. The maximum stability of antigorite is found at 680°C at 1.9 GPa,
which also corresponds to the maximum pressure limit for tremolite coexisting with olivine + orthopyroxene. The high aluminium
(3.70 wt% Al2O3) and chromium contents (0.59 wt% Cr2O3) of antigorite in the investigated starting material is responsible for the expansion of the serpentinite stability to 60–70°C
higher temperatures at 1.8 GPa than the antigorite stability calculated in the Al-free system. The antigorite from our study
has the highest Al–Cr contents among all experimental studies and therefore likely constraints the maximum stability of antigorite
in natural systems. Comparison of experimental results with olivine–orthopyroxene–chlorite–tremolite assemblages outcropping
in Cerro del Almirez indicates that peak metamorphic conditions were 680–710°C and 1.6–1.9 GPa. |
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