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Staurolite producing reactions and geothermobarometry of a high pressure thermal aureole in the French Massif Central
Author(s) -
DELOR C. P.,
BURG J. P.,
LEYRELOUP A. F.
Publication year - 1984
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1984.tb00285.x
Subject(s) - geothermobarometry , staurolite , kyanite , geology , geochemistry , massif , metamorphic rock , metamorphism , andalusite , biotite , sillimanite , mineralogy , petrology , paleontology , quartz
Biotite, garnet, staurolite and kyanite isograds in pelitic metasedimentary rocks are developed as a result of thermal metamorphism around syntectonic granitoids in Eastern Rouergue (France). Temperature estimates range between 400°C and 650°C at about 6.5 kbar. Geothermobarometry shows a steep isobaric T gradient which is consistent with the interpretation that the metamorphic highs are thermal aureoles. High grade rocks show evidence of two staurolite forming reactions in the presence of plagioclase and the absence of chlorite that have not been described previously in the literature. The reaction that occurs in the middle staurolite zone, alm‐rich ga + Ca‐rich pla + Na‐rich mu gro‐rich ga + Na‐rich pla + st + Na‐poor mu, is considered to be prograde, whereas the reaction that occurs in the kyanite zone, alm‐rich ga + Ca‐rich pla + w st + Ca‐rich ga + Na‐rich pla + qz, is retrograde. The topology of these reactions is illustrated in terms of end member compositions for the systems KNaFASH and KCaFASH, respectively.