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.
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
FIANNACCA, PATRIZIA;ORTOLANO, GAETANO;CIRRINCIONE, ROSOLINO;PEZZINO, Antonino
2012-01-01
Abstract
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.File | Dimensione | Formato | |
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