The Trikorfo area (Thassos Island, Rhodope massif, Northern Greece) represents a unique mineralogical localitywithMn-richminerals including kyanite, andalusite, garnet and epidote. Their vivid colors and large crystal sizemake themgood 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 andlocally inmetasomatic assemblageswith a large variety of colors (zonedblue 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+ andMn3+ 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 duringMiocene 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.
Metamorphic and Metasomatic Kyanite-Bearing Mineral Assemblages of Thassos Island (Rhodope, Greece)
Konstantinos Mavrogonatos;
2019-01-01
Abstract
The Trikorfo area (Thassos Island, Rhodope massif, Northern Greece) represents a unique mineralogical localitywithMn-richminerals including kyanite, andalusite, garnet and epidote. Their vivid colors and large crystal sizemake themgood 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 andlocally inmetasomatic assemblageswith a large variety of colors (zonedblue 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+ andMn3+ 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 duringMiocene 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
