PETROLOGICAL STUDY OF METAPELITIC GRAPHITIC SCHISTS FROM THE SOUTHWESTERN TAUERN WINDOW (EASTERN ALPS)

In the past, several studies aimed to investigate and analyze the Alpine metamorphism of rocks outcropping in the southwestern corner of the penninic Tauern Window. Within the Paleozoic cover sequence of the Lower Schieferhülle series (LSH), graphitic schists of sedimentary origin named “Furtschagl schists” crop out. Their characteristic metamorphic association is Grt+Bt+Pl+Qz+Ms+Ilm+GrChlEpSt, with Tur+Ap+Zrn as accessory minerals. In this thesis these graphitic schists are characterized with new petrological data, adopting a combined and multidisciplinary approach. Petrographic observations under the optical microscope, microchemical study conducted by Electron Probe Micro-Analyzer (EPMA) and by Scanning Electron Microscope - Energy Dispersive Spectroscopy (SEM-EDS) allowed to characterize the chemical composition of the mineral assemblage. The garnets are almandine-rich, in a percentage that increases from 68% at the core to 80% at the rim. Analyses of biotite indicate an XMg in the range 0.45-0.60, while the TiO2 content is in between 0.91 and 2.33 wt%. Chlorite has an XMg of 0.58. Compositional maps carried out on the peculiar “foliation-perpendicular” microboudinaged biotites of these rocks (see Salvadori 2023 Master Thesis for the microstructural study) verified the presence of no systematical changes between graphite-rich and graphite-poor sectors. The micro-Raman spectroscopy of carbonaceous material (RSCM) permitted to estimate the peak metamorphic temperature at 55250°C. Thermodynamic modelling of phase equilibria further allowed to constrain the pressure and temperature conditions experienced during metamorphism: the rocks appear to have equilibrated in the range 5-9 kbar and at a maximum temperature of 560-600°C.