Ba- and Ti-enriched dark mica from the UHP metasediments of the Seve Nappe Complex, Swedish Caledonides

We report on the occurrence of peculiar Ba- and Ti-enriched dark mica in metasedimentary rocks that underwent high-pressure metamorphism in the diamond stability field followed by decompression to granulite facies conditions. The mica occurs as well-developed preserved laths in a quartzofeldspathic...

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Bibliographic Details
Published in:Mineralogia 2015-06, Vol.46 (1), p.41-50
Main Authors: Majka, Jarosław, Kruszewski, Łukasz, Rosén, Åke, Klonowska, Iwona
Format: Article
Language:English
Subjects:
calcic gneiss
Scandinavian Caledonides
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Summary:We report on the occurrence of peculiar Ba- and Ti-enriched dark mica in metasedimentary rocks that underwent high-pressure metamorphism in the diamond stability field followed by decompression to granulite facies conditions. The mica occurs as well-developed preserved laths in a quartzofeldspathic matrix. The mean concentrations of BaO and TiO in the mica are 11.54 and 7.80wt%, respectively. The maximum amounts of these components are 13.38wt% BaO and 8.45wt% TiO . The mean crystallochemical formula can be expressed as (K Ba Na Ca (Fe Mg Ti Al Mn Cr (Si Al (OH , with , and siderophyllite as dominating end-members. Based on the petrographical observations, it is proposed that the dark mica was formed at a rather late stage in the evolution of the parental rock, i.e. under granulite facies conditions.
ISSN:1899-8526
1899-8291
1899-8526
DOI:10.1515/mipo-2017-0001