Abstract
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 different 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, different 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 different composition of mineralizing fluids. Stable isotopes of C and O also indicate such a different chemistry. In detail, samples from the Pietrapica site are characterized by δ13C fluctuations coupled with a δ18O shift documenting calcite formation in an open-system where mixing between deep and shallow fluids occurred. Conversely, δ13C and δ18O 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.
Highlights
Mantle peridotites are exposed on the seafloor at slow and ultraslow spreading mid-ocean ridges [1]
A total of 26 representative samples of serpentinites dominated by carbonate-veins (SpFA) and serpentinites dominated by quartz-carbonate veins (SpPP) were collected at the Fosso Arcangelo site, near the San Severino Lucano village, and in the Pietrapica site, at the Calabria-Lucanian boundary (Figure 1) (Table 1)
Lizardite + magnetite mesh texture or hourglass structures [74,75,76] usually occur in the serpentinites and cutting veins of Fosso Arcangelo (SpFA) showing showing cores of relict olivine grains replaced by calcite that locally are cross-cut by carbonate veins cores of relict olivine grains replaced by calcite that locally are cross-cut by carbonate veins (Figure 3c)
Summary
Mantle peridotites are exposed on the seafloor at slow and ultraslow spreading mid-ocean ridges [1]. Minerals 2020, 10, 127 volatile cycling and fluid mobile elements acting as a source for water, carbon, sulfur, chlorine, boron, arsenic, and nitrogen [9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26] These rocks, in the last years have been widely studied to gain a better understanding of their reactivity with respect to hydrothermal fluids promoting carbonation processes and mineral immobilization of large amounts of CO2 [27,28]. In southern Apennines, serpentinites occur as slices within the geological and structural frame of the Pollino Massif ophiolites (southern Ligurian Tethys) in the Ligurian Accretionary Complex (LAC) [37] These rocks are traversed by a complex network of veins with different textural and macroscopic features. Our principal goals are to define (1) source and composition of mineralizing fluids and (2) processes leading to mobilization, fractionation, and redistribution of chemical elements during the emplacement of the Frido Unit serpentinites within the accretionary wedge
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