An Integrated Study of the Serpentinite-Hosted Hydrothermal System in the Pollino Massif (Southern Apennines, Italy)

A comprehensive study of the serpentinite and associated veins belonging to the Frido Unit
in the Pollino Massif (southern Italy) is presented here with the aim to provide new constraints about
the hydrothermal system hosted by the accretionary wedge of the southern Apennines. The studied
serpentinites are from two di erent sites: Fosso Arcangelo and Pietrapica. In both sites, the rocks show
mylonitic-cataclastic structures and pseudomorphic and patch textures and are traversing by pervasive
carbonate and quartz-carbonate veins. The mineralogical assemblage of serpentinites consists of
serpentine group minerals (with a predominance of lizardite), amphiboles, pyroxene, chlorite, titanite,
magnetite, and talc. In some samples, hydro-garnet was also detected and documented here for
the first time. As for cutting veins, di erent mineralogical compositions were observed in the two
sites: calcite characterizes the veins from Fosso Arcangelo, whereas quartz and dolomite are the
principal minerals of the Pietrapica veins infill, suggesting a di erent composition of mineralizing
fluids. Stable isotopes of C and O also indicate such a di erent chemistry. In detail, samples from the
Pietrapica site are characterized by 13C fluctuations coupled with a 18O shift documenting calcite
formation in an open-system where mixing between deep and shallow fluids occurred. Conversely,
13C and 18O of the Fosso Arcangelo veins show a decarbonation trend, suggesting their developing
in a closed-system at deeper crustal conditions. Precipitation temperature calculated for both sites
indicates a similar range (80 C to 120 C), thus suggesting carbonate precipitation within the same
thermal system.