Thermodynamic modeling assisted by multivariate statistical image analysis as a tool for unraveling metamorphic P-T-d evolution: an example from ilmenite-garnet-bearing metapelite of the Peloritani Mountains, Southern Italy

An ilmenite-garnet-bearing schist from themedium-grade metapelite complex of the Mandanici Unit inthe Peloritani Mountains has been investigated to constrain theP-T conditions attained in this sector of the southern EuropeanHercynian chain. Microprobe investigations assisted by statisticalhandling of X-ray maps via principal component analysisallowed us to better elucidate the porphyroblast-matrixrelationships, the geometry of the elemental distribution ingarnet porphyroblasts and the average volume percentage ofthe reactant garnet during retrograde metamorphic evolution.Selected microprobe data were then used to constrain, bymeans of P-T pseudosections, the main P-T stages of themetamorphic evolution, using the XRF bulk-rock chemistryas the equilibrium chemical composition for the prograde andpeak stages and an effective bulk-rock composition for theretrograde one. Peak metamorphic P-T estimates (~530 °C;0.9 GPa) are consistent with a Hercynian crustal thickeningstage at middle-lower crustal conditions, while subsequentevolution, constrained at 420–460 °C; 0.30–0.60 GPa, depictsa retrograde clockwise P-T trajectory linked to exhumationunder likely extensional shearing conditions. The resultsobtained in this paper lead to envisage a new scenario forthe crustal evolution of the Peloritani Mountains and stimulatea revision of previous interpretations in the light of the newinvestigation techniques.