ORIGINAL PAPER 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 Patrizia Fiannacca & Deborah Lo Pò & Gaetano Ortolano & Rosolino Cirrincione & Antonino Pezzino Received: 29 November 2011 / Accepted: 8 October 2012 # Springer-Verlag Wien 2012 Abstract An ilmenite-garnet-bearing schist from the medium-grade metapelite complex of the Mandanici Unit in the Peloritani Mountains has been investigated to constrain the P-T conditions attained in this sector of the southern European Hercynian chain. Microprobe investigations assisted by sta- tistical handling of X-ray maps via principal component anal- ysis allowed us to better elucidate the porphyroblast-matrix relationships, the geometry of the elemental distribution in garnet porphyroblasts and the average volume percentage of the reactant garnet during retrograde metamorphic evolution. Selected microprobe data were then used to constrain, by means of P-T pseudosections, the main P-T stages of the metamorphic evolution, using the XRF bulk-rock chemistry as the equilibrium chemical composition for the prograde and peak stages and an effective bulk-rock composition for the retrograde one. Peak metamorphic P-T estimates (~530 °C; 0.9 GPa) are consistent with a Hercynian crustal thickening stage at middle-lower crustal conditions, while subsequent evolution, constrained at 420–460 °C; 0.30–0.60 GPa, depicts a retrograde clockwise P-T trajectory linked to exhumation under likely extensional shearing conditions. The results obtained in this paper lead to envisage a new scenario for the crustal evolution of the Peloritani Mountains and stimulate a revision of previous interpretations in the light of the new investigation techniques. Introduction Integrated microstructural and microprobe investigations are essential tools to obtain information about progressive folia- tion development, porphyroblast growth-timing and chemical zoning patterns, in turn necessary to constrain through geo- thermobarometry the different stages of pressure-temperature- deformation (P-T-d) evolution of metamorphic rocks. Significant advances in P-T path reconstructions have been made with the development of the techniques of thermody- namic modeling of representative samples via computation of P-T pseudosections (e.g. Holland and Powell 1998; White et al. 2000; Connolly and Petrini 2002; Connolly 2005, 2009). Nevertheless, high reliability of achieved constraints may be ensured only if the thermodynamically derived data closely match the actual structural and minerochemical features of studied rocks, with particular reference to the correct sequence of mineral equilibria (e.g. Zeh 2001; Gaidies et al. 2006; Cirrincione et al. 2008; Angì et al. 2010; Groppo and Castelli 2010). For this reason, the most detailed P-T paths have been usually obtained on medium-grade porphyroblastic metape- lites, known to be particularly well suited to reconstruct reliable sequences of blasto-deformational events. Indeed, lack of porphyroblasts in lower grade metamorphics often prevents to obtain meaningful blasto-deformational relation- ships while, in high-grade rocks, both earlier foliations and Editorial handling: G. Hoinkes P. Fiannacca : G. Ortolano (*) : R. Cirrincione : A. Pezzino Department of Biological, Geological and Environmental Sciences, University of Catania, Corso Italia 57, 95129 Catania, Italy e-mail: ortolano@unict.it D. Lo Pò Department of Earth and Geoenvironmental Sciences, University of Bologna, Piazza di Porta San Donato 1, 40126 Bologna, Italy Miner Petrol DOI 10.1007/s00710-012-0228-4