DEFORMATION IN QUARTZ AND CALCITE IN GREENSCHIST-FACIES ROCKS OF THE ALPI APUANE, CENTRAL ITALY.

The Alpi Apuane is a metamorphic core complex located in the Tuscan region of Italy, exposing a succession of tightly folded greenschist-facies quartz- and calcite-rich rocks. We aim to determine how quartz and calcite respond differently to the same applied strain, particularly in these rocks, because they are interlayered on the millimeter scale. Using a petrographic microscope, we analyzed microstructures and fabrics, minerals present, grain sizes, types of recrystallization, and evidence of deformation in the samples. We also utilized electron backscatter diffraction (EBSD) to determine the crystallographic orientations of calcite and quartz. EBSD allows us to identify which slip systems are active in calcite and quartz, the temperatures of deformation, and whether the rocks experienced coaxial or non-coaxial strain. Calcite, quartz, chlorite, biotite, and muscovite are the dominant minerals in the samples. In these samples, quartz grains range from <10 µm in diameter to 100–200 µm in diameter, and calcite grains are coarser, at diameters of ~200 µm up to 700–1000 µm. Sigmoidal quartz porphyroclasts with tails and mica fish give a shear sense of top to the south. We also identified C' and S fabrics defined by recrystallized biotite and chlorite grains in these samples and preliminary findings from C’ fabrics support top to the south shear sense. Initial EBSD data from quartz reveal interesting quartz c-axis pole figure results that suggest the shear zone has an atypical geometry. Further EBSD data was collected to compare how quartz and calcite respond to strain and better understand the shear zone geometry. We present our preliminary observations, including estimates of kinematic shear sense and deformation temperature based on quartz fabrics which constitute a relatively minor phase in the Alpi Apuane, and compare these results to existing estimates based on other more abundant phases.