Summary
Chemical, X-ray, optical, thermal and microprobe analyses have been carried out on six chlorites from Italian granitoid rocks formed as a result of deuteric action on biotites.
The data show that five chlorites, spanning ripidolite-brunsvigite fields, are IIb polytypes and therefore of high temperature origin. Only one sample is a thuringite, Ib (β=90°) polytype, typical of low temperature.
The occurrence of this last polytype, never mentioned in the literature from granitoid rocks, suggests a wider possibility for using chlorite polytypism in studying the late magmatic phenomena.
Résumé
On a fait des analyses chimiques, aux rayons X, optiques, termiques et à la microsonde électronique, de six chlorites, provenant de roches granitiques italiennes, dérivées par action hydrothermale sur des biotites. Les résultats montrent que cinq chlorites sont ripidolites-brunsvigites, du polytype IIb, et donc, de températures élevées. Seulement une est une thuringite, polytype Ib (β=90°), typique de températures basses.
La découverte de ce dernièr polytype, jamais cité dans la litérature, en roches granitiques, laisse prévoir la possibilité plus vaste d'employer le polytypisme des chlorites dans l'étude des phénomènes tard-magmatiques.
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Bondi, M., Morten, L. & Rossi, P.L. Chlorites from Italian granitoid rocks. TMPM Tschermaks Petr. Mitt. 23, 39–50 (1976). https://doi.org/10.1007/BF01081868
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DOI: https://doi.org/10.1007/BF01081868