Ligurian hyperextended continental margin preserved in an ophiolitic block at Timpa di Pietrasasso, Calabrian Arc, southern Italy

Abstract

ABSTRACT The Cenozoic accretionary complex in the Calabrian Arc, southern Italy, contains hectometric- to kilometric-scale exposures of basalt, gabbro, and serpentinite that have been interpreted as dismembered fragments of Alpine Tethys ocean crust because of their incomplete nature with respect to the traditional view of a complete ophiolite sequence. We present new geologic mapping, geochemistry, and geochronology of one of these units at Timpa di Pietrasasso near the town of Terranova di Pollino in the Basilicata region that exposes Jurassic Tethyan pillow basalt and chert that are separated from gabbro and serpentinite by a fault. The gabbro in the footwall is Permian in age, indicated by U-Pb zircon ages of 284 ± 6 Ma, 293 ± 6 Ma, and 295 ± 4 Ma, linking it to gabbros that underplated continental crust after the Permo-Carboniferous Variscan Orogeny. The gabbro first underwent amphibolite-facies metamorphism, then developed a greenschist-facies mylonitic foliation near the fault surface that is crosscut by undeformed Jurassic-aged dikes of Tethyan origin, indicating that deformation is early Tethyan or pre-Tethyan in age. The underlying serpentinite is tectonically interleaved with blocks of Variscan lower crust, indicating that the missing upper plate of the extensional detachment complex was continental in origin. These features indicate that the Timpa di Pietrasasso unit preserves a low-angle detachment fault that developed in a hyperextended continental margin of the Alpine Tethys.