Mn-Andalusite, Spessartine, Mn-Grossular, Piemontite and Mn-Zoisite/Clinozoisite From Trikorfo, Thassos Island, Greece

Abstract

Mylonitized manganiferous schists and calc-silicate layers intercalated within amphibolite-to greenschist facies mica schists from the Trikorfo area (Thassos Island, Greece), host an unusual Mn-rich paragenesis of metamorphic silicate minerals, most of them in large, gemmy crystals. The silicates occur both in layers subparallel to the foliation and within discordant veins cross-cutting the metamorphic fabric. Piemontite (up to 12.7 wt. % Mn2O3), , , , spessartine (up to 47.7 wt. % MnO) and

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

“…In general the crystals are zoned with dark blue cores and green-transparent (Figure 4b An orthogneiss exposed in the area is composed of orthoclase, oligoclase/andesine along with phlogopite, quartz, hematite, epidote and allanite and is surrounded by a transitional zone with the same mineralogy as the above mentioned calc-silicate layers (i.e. amphibole, plagioclase, and epidote mineral groups from granitoid outwards) [20]. The presence of pluricentimetric crystals of tourmaline (schorl mainly) was also shown in quartz veins and late brittle fissures [20].…”

“…These mica schists are thus likely derived from calcareous pelitic sediments [24]. Interestingly, this unit also locally presents uncommon Mn-rich mineral assemblages attributed to post-metamorphic hydrothermal recrystallization [20,24,26]. The garnet-kyanite-biotite-hematite-plagioclase ± staurolite ± sillimanite paragenesis of the mica schists, contemporaneous with the ductile fabric related to extensional deformation, has been specifically interpreted as having attained PT conditions of 5.5 ± 1.5 kbars and 600 ± 50 • C, without any evidence of partial melting [24].…”

“…The garnet-kyanite-biotite-hematite-plagioclase ± staurolite ± sillimanite paragenesis of the mica schists, contemporaneous with the ductile fabric related to extensional deformation, has been specifically interpreted as having attained PT conditions of 5.5 ± 1.5 kbars and 600 ± 50 • C, without any evidence of partial melting [24]. Voudouris et al [20] documented at the top of the formation the presence of an orthogneiss at the contact with the paragneisses/mica schists. Although not exposed, a granitoid is considered to be genetically related to the widespread Miocene gold mineralization in the area [27].…”

“…The geology of Greece is marked by a recent alpine belt, which results in outstanding localities for minerals and gemstones owing to high PT metamorphic conditions and subsequent magmatism and hydrothermalism, e.g., [19][20][21][22][23]. Among these localities, the island of Thassos, in the Rhodope Belt, represents a unique mineralogical locality for kyanite and uncommon varieties of manganiferous/manganian and magnesian silicate and calc-silicate minerals, including garnet, andalusite and epidote among others [19,[24][25][26][27][28][29][30][31].…”

“…On the basis of the description made by Voudouris et al [20], the aim of the present study is (i) to obtain a complete inventory of the metamorphic and metasomatic minerals and their assemblages found at the Trikorfo site, (ii) to evaluate the cation substitution responsible for the color variations, (iii) to reevaluate the PT conditions attained by the gneiss host-rock on the basis of a comprehensive petrological phase equilibria using the Perple_X program, and (iv) to discuss the conditions of formation, metamorphic versus metasomatic, of these exceptional parageneses and assemblages of (Mn-rich)-silicate and calc-silicate minerals. Kyanite, as a ubiquitous silicate found in both metamorphic and localized metasomatic assemblages, is the referent mineral described in the manuscript.…”