Tschermak's substitution in antigorite and consequences for phase relations and water liberation in high-grade serpentinites

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• 作者：Jos¨¦ Alberto Padr¨®n-Navarta ; Vicente L¨®pez S¨¢nchez-Vizca¨ªno ; Joerg Hermann ; James A.D. Connolly ; Carlos J. Garrido ; Mar¨ªa Teresa G¨®mez-Pugnaire ; Claudio Marchesi
• 关键词：Antigorite ; Tschermak's exchange ; Geothermobarometry ; Serpentinite ; Dehydration ; Subduction zones
• 刊名：Lithos
• 出版年：2013
• 出版时间：15 September, 2013
• 年：2013
• 卷：178
• 期：Complete
• 页码：186-196
• 全文大小：645 K

文摘

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 3.6 wt. % Al₂O₃ at 20 kbar-650 ¡ãC and of 4.5 wt. % Al₂O₃ at 3 kbar-560 ¡ãC. 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 (> 1.8 wt. % ) and is widespread in lherzolites, where it occurs together with diopside or, in a narrow temperature field, with tremolite.