Séminaire de Giovanni B. Andreozzi, Professeur invité

Granitic pegmatite evolution studied via tourmaline single-crystal chemical zoning

Jeudi 3 mai 2018 à 10h30

Salle 401 - 4e étage - Couloir 22-23
IMPMC - Campus de Jussieu
Sorbonne Université
4 place Jussieu - 75005 Paris

Abstract

The present study is focused on the comparison of crystal chemistry of a large color-zoned tourmaline crystal and tourmaline chemical evolution in the internally-zoned Cruzeiro pegmatite, Brazil. The tourmaline sample investigated here is a prismatic, multi-colour-zoned single crystal, ca. 8 cm large and 10 cm long, characterized by a large, homogeneous black core in contact with a narrow blue inner rim and a thicker outer green rim. Four crystal fragments were extracted and investigated by X-ray diffraction and structure refinement, electron microprobe analysis, Mössbauer spectroscopy and optical absorption spectroscopy. Tourmaline chemical variation from core to rim is defined in terms of site population at the Y site (Al, Fe, Li etc.) and at the O1 site (O, OH, F): the zoned crystal evolved from black schorl to blue and green fluor-elbaite, that is with concomitant reduction of Fe2+ and enrichment of (Al+Li) as well as of F due to increasing melt fractionation. Along this path, a very good negative correlation between F and Fe2+ was observed, nicely approximated by the linear trend F = 1 - 033Fe2+ (apfu), which drives tourmaline composition from schorl to fluor-elbaite.

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Présent du 18 avril au 18 mai : 

Sapienza University of Rome, Department of Earth Sciences - Italie

Invité par Daniele Antonangeli de l'IMPMC.

Current position : Associate Professor (with National scientific habilitation as Full Professor) • Director of Doctoral School “Vito Volterra” in Astronomy, Astrophysics, Chemistry, Earth Sciences, Mathematics, and Physics.

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