<abstract xmlns="http://www.w3.org/1999/xhtml">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 TiO2 in the mica are 11.54 and 7.80wt%, respectively. The maximum amounts of these components are 13.38wt% BaO and 8.45wt% TiO2. The mean crystallochemical formula can be expressed as (K0.54Ba0.39Na0.02Ca0.01)Σ0.96(Fe1.37Mg0.85Ti0.50Al0.29Mn0.01Cr0.01)Σ3.03(Si2.59Al1.41)Σ4.00O10(OH1.30O0.66F0.02S0.01)Σ1.99, with <italic>oxyannite</italic>, <italic>oxy-ferrokinoshitalite</italic> 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.</abstract>

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 TiO2 in the mica are 11.54 and 7.80wt%, respectively. The maximum amounts of these components are 13.38wt% BaO and 8.45wt% TiO2. The mean crystallochemical formula can be expressed as (K0.54Ba0.39Na0.02Ca0.01)Σ0.96(Fe1.37Mg0.85Ti0.50Al0.29Mn0.01Cr0.01)Σ3.03(Si2.59Al1.41)Σ4.00O10(OH1.30O0.66F0.02S0.01)Σ1.99, with oxyannite, oxy-ferrokinoshitalite 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.

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

Uppsala University, CEMPEG – Department of Earth Sciences, Villavägen 16, SE – 752 36 Uppsala,

AGH – University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection, al. Mickiewicza 30, 30-059 Kraków,

Polish Academy of Sciences, Institute of Geological Sciences, ul. Twarda 51/55, 00-818 Warszawa,

University of Bern, Institute of Geological Sciences, Baltzerstrasse 1+3, CH-3012 Bern,

Mineralogia

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

We report on the occurrence of peculiar Ba- and Ti-enriched dark mica in metasedimentary rocks that underwent high-pressure metamorphism in the diamond...

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

Published Online: Feb 18, 2017

Page range: 41 - 50

Received: Jan 25, 2016

Accepted: Oct 10, 2016

DOI: https://doi.org/10.1515/mipo-2017-0001

Keywords
calcic gneiss, Scandinavian Caledonides

© 2015 Jarosław Majka et al., published by De Gruyter Open

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

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

Published Online: Feb 18, 2017

Page range: 41 - 50

Received: Jan 25, 2016

Accepted: Oct 10, 2016

DOI: https://doi.org/10.1515/mipo-2017-0001

Keywordscalcic gneiss, Scandinavian Caledonides

© 2015 Jarosław Majka et al., published by De Gruyter Open

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Keywords
calcic gneiss, Scandinavian Caledonides