Hydration of orthopyroxene–cordierite-bearing assemblages at Laouni, Central Hoggar, Algeria |
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| Authors: | M GUIRAUD R POWELL & J-Y COTTIN |
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| Institution: | Laboratoire de Minéralogie, URA CNRS No. 736, Muséum National d'Histoire Naturelle, 61 rue Buffon, 75005 Paris, France (guiraund @ cimrs1.mnhn.fr),;Department of Geology, The University of Melbourne, Parkville, Victoria, 3052, Australia,;Laboratoire de Géologie-Pétrologie, URA CNRS No. 10, Facultédes Sciences et Techniques, Universitéde Saint Etienne,23 rue du Docteur Michelon, 42023 Saint Etienne Cedex2, France |
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| Abstract: | In the Laouni region (Central Hoggar, Algeria), retrogression of high-grade orthopyroxene–cordierite-bearing rocks led to the crystallization of orthoamphibole and garnet, and at a later stage of chlorite, from the original paragenesis. Calculated phase diagrams show that this retrogression occurred at about 3 kbar with the simplest model involving hydration at 650–700° C and at around 500° C, with the rocks experiencing a H2O less than 1, except possibly in the last stages of chlorite crystallization. As the other rock types occurring in the same area as the orthopyroxene–cordierite rocks display similar features, it is concluded that regional hydration occurred, presumably related to the release of fluids during the crystallization of the Pan-African granitic and mafic magmas that are widespread in the Laouni area. |
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| Keywords: | cordierite Hoggar hydration orthoamphibole orthopyroxene |
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