Garnet re-equilibration by coupled dissolution-reprecipitation: evidence from textural, major element and oxygen isotope zoning of 'cloudy' garnet

The analysis of texture, major element and oxygen isotope compositions of cloudy garnet crystals from a metapelite sampled on Ikaria Island (Greece) is used to assess the model of growth and re-equilibration of these garnet crystals and to reconstruct the pressure-temperature-fluid history of the sample. Garnet crystals show complex textural and chemical zoning. Garnet cores (100-200μm) are devoid of fluid inclusions. They are characterized by growth zoning demonstrated by a bell-shaped profile of spessartine component (7-3mol.%), an increase in grossular from 14 to 22mol.% and δ18O values between 9.5±0.3‰ and 10.4±0.2‰. Garnet inner rims (90-130μm) are fluid inclusion-rich and show a decreasing grossular component from 22 to 5mol.%. The trend of the spessartine component observed in the inner rim allows two domains to be distinguished. In contrast to domain I, where the spessartine content shows the same trend as in the core, the spessartine content of domain II increases outwards from 2 to 14mol.%. The δ18O values decrease towards the margins of the crystals to a lowest value of 7.4±0.2‰. The outer rims (<10μm) are devoid of fluid inclusions and have the same chemical composition as the outermost part of domain II of the inner rim. Garnet crystals underwent a four-stage history. Stage 1: garnet growth during the prograde path in a closed system for oxygen. Garnet cores are remnants of this growth stage. Stage 2: garnet re-equilibration by coupled dissolution-reprecipitation at the temperature peak (630<T