A systematic approach to reconstruct ophiolite tectonic setting and paleo-position from outcrop analysis and geochemistry: the example of the North Calabria Unit (Southern Apennines, Italy)

Ophiolites derive from different tectonic settings, including mid-ocean ridges (MOR), supra-subduction zones (SSZ), and ocean–continent transitions (OCT). However, discriminating among these settings and relocating ophiolitic fragments nowadays in orogens to their original paleo-position in space and time remains challenging.

This study aims at constraining the original tectonic setting and paleo-position of three isolated and fragmented ophiolite slivers belonging to the North Calabria Unit (Basilicata region, southern Italy). The North Calabria Unit represents a strongly dismembered association of mantle, mafic, and continental crustal rocks incorporated into the southern Apennine orogenic system. These units are interpreted as remnants of the Jurassic Alpine Tethys, later affected by Alpine–Apennine convergence and tectonic reworking.

We investigate three ophiolite slivers using a multiscale approach integrating detailed field observations, petrological and geochemical analyses, zircon geochronology, and plate-kinematic reconstructions. Particular emphasis is placed on the characteristics of key lithologies and, critically, on the nature of their contacts, which provide first-order constraints on the original tectonic setting of these slivers.

Key observations include: (i) Mid-Jurassic cherts stratigraphically overlying MOR-type basalts, sealing tectonic contacts between depleted mantle and gabbros affected by crustal contamination; (ii) amphibolite and gneiss tectonically juxtaposed with gabbros, with zircon age and composition compatible with  a pre-rift lower continental crustal origin; and (iii) the possible circulation of Cr-rich, mantle-derived fluids along low-angle faults at the top of continental crustal rocks.

When integrated with kinematic reconstructions, these observations indicate that the studied ophiolite slivers originated in an OCT setting developed during Jurassic rifting of the European side of the Alpine Tethys, possibly near Sardinia, rather than in a fully oceanic MOR or SSZ environment.

Our workflow provides a framework to locate fragmented ophiolites in rifted margins and can be applied to interpret dismembered ophiolites in orogenic belts worldwide.