TY - JOUR
T1 - Tschermak's substitution in antigorite and consequences for phase relations and water liberation in high-grade serpentinites
AU - Padrón-Navarta, José Alberto
AU - Sánchez-Vizcaíno, Vicente López
AU - Hermann, Joerg
AU - Connolly, James A.D.
AU - Garrido, Carlos J.
AU - Gómez-Pugnaire, María Teresa
AU - Marchesi, Claudio
PY - 2013/9/5
Y1 - 2013/9/5
N2 - A model for the incorporation of alumina in FeO-MgO-Al2O3-SiO2-H2O (FMASH) serpentinites has been developed by considering ideal Tschermak (Al2Mg-1Si-1) solid solution in antigorite. The antigorite model has been calibrated by fitting the experimental conditions for the decomposition of antigorite to chlorite+olivine+orthopyroxene+fluid in the FMASH system. The antigorite Al-contents predicted with this model are in agreement with natural observations and suggest a maximum alumina solubility in antigorite of 3.6wt.% Al2O3 at 20kbar-650°C and of 4.5wt.% Al2O3 at 3kbar-560°C. In the assemblage antigorite-olivine-chlorite-fluid, the Al-content of antigorite is buffered and temperature sensitive. This temperature sensitivity is the basis for a serpentinite geothermometer at greenschist, amphibolite and eclogite facies conditions. The buffered assemblage is stable in harzburgite compositions for relatively moderate amounts of Al2O3 (>1.8wt.%) and is widespread in lherzolites, where it occurs together with diopside or, in a narrow temperature field, with tremolite.
AB - A model for the incorporation of alumina in FeO-MgO-Al2O3-SiO2-H2O (FMASH) serpentinites has been developed by considering ideal Tschermak (Al2Mg-1Si-1) solid solution in antigorite. The antigorite model has been calibrated by fitting the experimental conditions for the decomposition of antigorite to chlorite+olivine+orthopyroxene+fluid in the FMASH system. The antigorite Al-contents predicted with this model are in agreement with natural observations and suggest a maximum alumina solubility in antigorite of 3.6wt.% Al2O3 at 20kbar-650°C and of 4.5wt.% Al2O3 at 3kbar-560°C. In the assemblage antigorite-olivine-chlorite-fluid, the Al-content of antigorite is buffered and temperature sensitive. This temperature sensitivity is the basis for a serpentinite geothermometer at greenschist, amphibolite and eclogite facies conditions. The buffered assemblage is stable in harzburgite compositions for relatively moderate amounts of Al2O3 (>1.8wt.%) and is widespread in lherzolites, where it occurs together with diopside or, in a narrow temperature field, with tremolite.
KW - Antigorite
KW - Dehydration
KW - Geothermobarometry
KW - Serpentinite
KW - Subduction zones
KW - Tschermak's exchange
UR - http://www.scopus.com/inward/record.url?scp=84882820280&partnerID=8YFLogxK
U2 - 10.1016/j.lithos.2013.02.001
DO - 10.1016/j.lithos.2013.02.001
M3 - Article
SN - 0024-4937
VL - 178
SP - 186
EP - 196
JO - Lithos
JF - Lithos
ER -