Age constraints on Late Paleozoic evolution of continental crust from electron microprobe dating of monazite in the Peloritani Mountains (southern Italy): another example of resetting of monazite ages in high-grade rocks

In situ monazite microprobe dating has beenperformed, for the first time, on trondhjemite andamphibolite facies metasediments from the PeloritaniMountains in order to obtain information about the age ofmetamorphism and intrusive magmatism within this stillpoorly known sector of the Hercynian Belt. All samplesshow single-stage monazite growth of Hercynian age. Onemigmatite and one biotitic paragneiss yielded monaziteages of 311 ± 4 and 298 ± 6 Ma, respectively. These agesfit with previous age determinations in similar rocks fromsouthern Calabria, indicating a thermal metamorphic peakat about 300 Ma, at the same time as widespread granitoidmagmatism. The older of the two ages might represent aslightly earlier event, possibly associated with theemplacement of an adjacent trondhjemite pluton, previouslydated by SHRIMP at 314 Ma. No evidence for pre-Hercynian events and only a little indication for somemonazite crystallization starting from ca. 360 Ma wereobtained from monazite dating of the metasediments,suggesting either a single-stage metamorphic evolution or asignificant resetting of the monazite isotope system duringthe main Hercynian event (ca. 300 Ma). Rare monazitefrom a trondhjemite sample yields evidence for a late-Hercynian age of about 275 Ma. This age is interpreted asrepresenting a post-magmatic stage of metasomatic monazitecrystallization, which significantly postdates theemplacement of the original magmatic body.