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Metamorphic and Metasomatic Kyanite-Bearing Mineral Assemblages of Thassos Island (Rhodope, Greece)

1
GeoRessources, Faculté des Sciences et Technologies, Université de Lorraine, CNRS, F-54506 Vandœuvre-lès-Nancy, France
2
Department of Geology & Geoenvironment, National and Kapodistrian University of Athens, 15784 Athens, Greece
3
Département de Géologie et de Génie Géologique, Université Laval, Québec, QC G1V 0A6, Canada
4
Laboratoire de Planétologie et Géodynamique, Université de Nantes, CNRS UMR 6112, 44322 Nantes, France
5
PANGEA Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052 Australia
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(4), 252; https://doi.org/10.3390/min9040252
Received: 27 February 2019 / Revised: 19 April 2019 / Accepted: 23 April 2019 / Published: 25 April 2019
(This article belongs to the Special Issue Mineralogy and Geochemistry of Gems)
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Abstract

The Trikorfo area (Thassos Island, Rhodope massif, Northern Greece) represents a unique mineralogical locality with Mn-rich minerals including kyanite, andalusite, garnet and epidote. Their vivid colors and large crystal size make them good indicators of gem-quality materials, although crystals found up to now are too fractured to be considered as marketable gems. The dominant lithology is represented by a garnet–kyanite–biotite–hematite–plagioclase ± staurolite ± sillimanite paragneiss. Thermodynamic Perple_X modeling indicates conditions of ca. 630–710 °C and 7.8–10.4 kbars. Post-metamorphic metasomatic silicate and calc-silicate (Mn-rich)-minerals are found within (i) green-red horizons with a mineralogical zonation from diopside, hornblende, epidote and grossular, (ii) mica schists containing spessartine, kyanite, andalusite and piemontite, and (iii) weakly deformed quartz-feldspar coarse-grained veins with kyanite at the interface with the metamorphic gneiss. The transition towards brittle conditions is shown by Alpine-type tension gashes, including spessartine–epidote–clinochlore–hornblende-quartz veins, cross-cutting the metamorphic foliation. Kyanite is of particular interest because it is present in the metamorphic paragenesis and locally in metasomatic assemblages with a large variety of colors (zoned blue to green/yellow-transparent and orange). Element analyses and UV-near infrared spectroscopy analyses indicate that the variation in color is due to a combination of Ti4+–Fe2+, Fe3+ and Mn3+ substitutions with Al3+. Structural and mineralogical observations point to a two-stage evolution of the Trikorfo area, where post-metamorphic hydrothermal fluid circulation lead locally to metasomatic reactions from ductile to brittle conditions during Miocene exhumation of the high-grade host-rocks. The large variety of mineral compositions and assemblages points to a local control of the mineralogy and fO2 conditions during metasomatic reactions and interactions between hydrothermal active fluids and surrounding rocks. View Full-Text
Keywords: kyanite; Mn-rich silicates; Rhodope; Thassos; amphibolite facies; metasomatism kyanite; Mn-rich silicates; Rhodope; Thassos; amphibolite facies; metasomatism
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Tarantola, A.; Voudouris, P.; Eglinger, A.; Scheffer, C.; Trebus, K.; Bitte, M.; Rondeau, B.; Mavrogonatos, C.; Graham, I.; Etienne, M.; Peiffert, C. Metamorphic and Metasomatic Kyanite-Bearing Mineral Assemblages of Thassos Island (Rhodope, Greece). Minerals 2019, 9, 252.

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