2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 75-12
Presentation Time: 4:50 PM


SHIMABUKURO, David H.1, BATTISTELLA, Claire1 and ALVAREZ, Walter2, (1)Department of Geology, California State University, Sacramento, CA 95819, (2)Department of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720-4767, dhs@csus.edu

Exposures of Tethyan ophiolite units preserved in Southern Italy have usually been interpreted to be dismembered or incomplete fragments of ocean crust due to an attenuated ophiolitic architecture. Instead, we suggest that they preserve complete sections of ocean-continent transition crust or oceanic core complexes, similar to those found in the Northern Apennines and Alps. There, missing ophiolitic elements are due to low-angle normal faulting in a magma-poor rift zone.

Mapping of a km-scale basalt-gabbro-serpentinite ophiolitic block at Timpa Pietrasasso near Terranova di Pollino demonstrates typical features of these non-Penrose-style ophiolites. The structurally highest pillow basalt and breccias commonly have interpillow spaces or small lenses filled with sedimentary serpentinite or chert. The volcanic and sedimentary unit is in contact with strongly foliated gabbro indicating the presence of an oceanic low-angle normal fault between them. The underlying serpentinite contains metasomatized rodingite dikes and Hercynian lower-crustal blocks that record a 193±2 Ma amphibolite-facies event.

To the south, at Monte Reventino, greenschist-facies metabasalt is juxtaposed against serpentinite. Serpentinite in the footwall has locally been altered by carbon-dioxide-rich fluids to ophicarbonate. Near the contact between the basalt and serpentinite, ophicarbonate has been metamorphosed into a talc-tremolite schist. Similar features exist at the ophiolitic exposures at Gimigliano.

Together, these exposures indicate that the serpentinite and gabbro preserved in Calabria were exhumed along low-angle oceanic detachment faults. These faults were developed at relatively high temperature, as indicated by the mylonitic fabric at Timpa Pietrasasso and talc-tremolite alteration of ophicarbonate at Monte Reventino. At Timpa Pietrasasso, the presence of Hercynian blocks in the serpentinite suggest continental crust was present in the hanging wall of the normal fault, indicating an ocean-continent transition environment. At Monte Reventino, no continental material is associated with the ophiolite, leaving open the possibility of a setting at an oceanic core complex. It is not yet clear whether the overlying basalt was erupted onto an exhumed surface, or if it was juxtaposed by fault activity.