INTERACTION BETWEEN DEFORMATION AND METAMORPHISM OF MARBLE, NAXOS, GREECE

We examined the interaction of deformation and metamorphism on mineral chemistry and textures in metacarbonates across a temperature and strain gradient. The island of Naxos, Greece has undergone two phases of metamorphism and deformation: Cretaceous subduction, which resulted in blueschist-grade conditions (M1) and a Miocene mid-amphibolite facies metamorphism (M2). M2 resulted in a large migmatite-cored dome capped by a Barrovian sequence of marbles and schists. We analyzed dolomite and calcite in six samples ranging, from west to east, from the eastern edge of dome (structurally lowest sample) to the eastern detachment that separates marble and schist from Tertiary conglomerate. Calcite-dolomite textures vary with location in the transect. Samples near the dome have coarse grains (~1-1.5mm) with straight boundaries, possibly from thermally controlled grain growth. The sample nearest the detachment shows evidence of subgrain rotation recrystallization (SGRR), with relatively straight grain boundaries. Samples structurally in the middle have lobate boundaries with calcite in the triple junctions of the dolomite, resulting from grain boundary migration (GBM). The presence of pinning microstructures suggests that dolomite grains are consuming calcite grains as deformation progresses. Calcite in marble close to the dome and the detachment is enriched in Mg (XMg ~ 0.031-0.038) compared with structurally intermediate samples, which contain lower Mg concentrations (XMg ~ 0.017-0.020). Bulk composition of each sample plotted against spatial distribution exhibits the same trend as the XMg in calcite. This trend corresponds with the observation that pure calcite marbles are found more commonly near the dome and detachment. Cation diffusion in calcite and dolomite is not effective at temperatures less than 500°C, which is above the estimated peak temperature for most of the studied samples. Enriched XMg may result from mobilization of Mg through grain growth and SGRR, while GBM in structurally intermediate samples did not significantly change mineral chemistry. In Naxos marble, bulk composition appears to be closely related to deformation.