The Tethyan roots of the Hyblean-Pelagian foreland domain (Sicily): geodynamic implications and possible modern analogues.

Hyblean diatremic tuff-breccia deposits, Late Tortonian in age, host an assorted variety of wall-rock xenolithsproviding the unique opportunity to directly investigate the unexposed lithosphere of south-eastern Sicily. Petrologicand geochemical studies on ultramafic and gabbroic xenoliths, along with a reappraisal of existing geological andgeophysical data, confirmed that the volcano-sedimentary sequence of this region lies upon the rest of the Ionian-TethysOcean basement, Permian in age, and hence suggested that the entire Sicily mainland and large part of its Pelagianoffshore areas are set upon a largely serpentinized ultramafic basement (Manuella et al., 2013; 2015). In particular,Hyblean xenoliths point to the occurrence of buried Oceanic Core Complex (OCC) structures. These are fault-boundedabyssal highs of serpentinized mantle peridotites and gabbroic rocks exhumed to the ocean floor along detachmentsystems in the crest zone of modern (ultra)slow-spreading mid-ocean ridges. Some structural, morphologic and seismicfeatures of the present Ionian-Pelagian-Hyblean foreland domain suggest that Core Complex systems likewise the St.Peter and St. Paul Megamullion (Equatorial MAR), the Atlantis Massif (MAR 30° N) and Rio Grande Rise (SouthWestern Atlantic), can be considered as modern analogues of the buried Tethyan OCC structures. Furthermore, theoccurrence of Tethyan serpentinites in the Sicily basement may imply that abundant marine salts formed in these rocksas the result of seawater-driven serpentinization. These deep-seated salts may have been remobilized by supercriticalfluids, which generated saline brines that emplaced at the sea bottom as hypersaline ponds, originating the Triassic andMessinian "Evaporites" in Sicily, as currently observed in the Red Sea floor (Hovland et al., 2015).Hovland M., Rueslåtten H. & Johnsen H.K. 2015. Red Sea salt formations-a result of hydrothermal processes. In: RasulN.M.A. & Stewart I.C.F. Eds. The Red Sea. Springer-Verlag, Berlin Heidelberg, 187–203.Manuella F.C., Brancato A., Carbone S. & Gresta S. 2013. A crustal upper mantle model for southeastern Sicily (Italy)from the integration of petrologic and geophysical data. J. Geodyn., 66, 92–102.Manuella F.C., Scribano V., Carbone S. & Brancato A. 2015. The Hyblean xenolith suite (Sicily): an unexpected legacyof the Ionian–Tethys realm. Int. J. Earth Sci., doi: 10.1007/s00531-015-1151-9.