Abstract
The hyperaluminous rocks from Vanoise occur on the western border of the basement of southern Vanoise (internal part of Briançonnais zone) and on the « zone houillère » (external part of Briançonnais) . The most characteristic assemblages are : 1) Pyrophyllite-diaspore-magnesiocarpholite ± chloritoïd ± paragonite ± chlorite + white mica. 2) Chloritoïd-white mica-paragonite ± chlorite. The cracks with a paragonite filling are abundant in all the hyperaluminous rocks and they suggest a sodic enrichment, the role of which is discussed as for the unstability of some minerals. Due to the coexistence of diaspore-pyrophyllite and the Si⁴ = 3,2 content of phengite the temperature and pressure of metamorphism was around 360° C and 5 kb.
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More From: Bulletin de la Société française de Minéralogie et de Cristallographie
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