Reply to “Comment on Manuella et al. ‘The Hyblean xenolith suite (Sicily): an unexpected legacy of the Ionian–Tethys realm’ by Beccaluva et al. (2015)”

Abstract

One of the most important pieces of background information left in our pen (Manuella et al. 2015) regards the circumstance that, during the last 25 years, international marine geology expeditions brought crucial advances in understanding the composition and tectonic evolution of present and fossil oceanic lithosphere (e.g., Pearce 2002; Dick et al. 2003; Boschi et al. 2006; Snow and Edmond 2007; Ildefonse et al. 2007; Miranda and Dilek 2010; Silantyev et al. 2011). In particular, we would draw attention to some fault-bounded abyssal highs, called oceanic core complexes (OCCs), located in the crest zone of (ultra) slow-spreading mid-ocean ridges. OCCs mostly consist of serpentinized mantle peridotites and gabbroic rocks exhumed to the ocean floor along systems of detachment faults, related to serpentinite diapirism. Most elevated blocks even reach the ocean surface to form non-volcanic ocean islands, as well as the St. Peter and St. Paul Rocks located near the axial zone of MAR in the equatorial region (e.g., Campos et al. 2010; Sharkov 2012). More in general, magmatic layers of the normal oceanic crust are very thin or even absent at OCCs sites, seismic profiles being compatible with a serpentinite layer overlying almost unaltered mantle ultramafics (e.g., Blackman et al. 2004a, b). In this respect, the concept of a “crust” had to be called into question, and hence, the Moho can be regarded as a serpentinization front (e.g., Minshull et al. 1998). Oxide-rich gabbros with sheared texture are considered obliged components of the gabbroic suite of present and fossil OCCs (e.g., Sharkov 2012). Veins of plagiogranites are also relatively common in these oceanic structures, intruding both gabbros and peridotite bodies. Oxide gabbros and plagiogranites from OCCs typically bear zircon as accessory phase (e.g., Aranovich et al. 2013). OCC basalts, Introduction