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.

ABSTRACT A broad synform in the Balagne region of northern Corsica (France) comprises the most complete remnant of the southwestern Alpine foreland basin and associated orogenic wedge, which have been otherwise fragmented and mostly eroded by a late Cenozoic postcollisional episode of microplate dispersal along the southern European continental margin. The Upper Cretaceous–Eocene turbidites of the Balagne region record the opening and subsequent progressive closure of the Ligurian-Piedmont ocean, the main branch of the Alpine Tethys in the Western Mediterranean. Sandstone detrital modes (gross and heavy-mineral compositions) of the Balagne turbidites can be compared with those of age-equivalent lithostratigraphic units of the western Alps and the Northern Apennines, thus defining broad sediment paleodispersal patterns and providing compelling paleogeographic constraints on the transition from pre-orogenic passive-margin to synorogenic foreland sedimentation. Upper Cretaceous turbidites of the Novella and Alturaia Formations were deposited along the northeastern (European) margin of the narrow Ligurian-Piedmont ocean. In contrast, the mixed carbonate/siliciclastic turbidites of the Upper Cretaceous Narbinco Formation have a distinct composition relative to the age-equivalent Novella and Alturaia Formations and cannot have been derived from the same sediment source area of the Helminthoid Flysch of the Northern Apennines and the Ligurian Alps. The Middle Eocene Balagne foreland basin fill represents a phase of sediment underfilling during the progressive flexure of the Corsican foreland in front of the advancing Alpine orogenic wedge. The basin-fill succession consists of, from bottom to top: (1) continental-to-transitional conglomerate and sandstone filling paleodepressions within the foreland basement complex; (2) thin and discontinuous nummulitic limestone capping—and partly lateral equivalent to—the basal conglomerate; (3) hemipelagic pelite; and (4) a thick turbidite section.

Abstract We investigate the structural, petrological and compositional features recorded by strongly deformed and melt-percolated Erro–Tobbio peridotites (Voltri Massif, Ligurian Alps, NW Italy), in order to demonstrate that the processes of shear-zone formation and melt percolation are intimately linked by a positive feedback. We focus on spinel and plagioclase peridotites, and extensional shear zones that underwent infiltration by upwelling asthenospheric melts. Shear and porosity bands, which developed during extension prior to melt infiltration, represent important structural and rheological pathways to facilitate and enhance melt infiltration into the extending lithosphere and the ascent of such melts to shallower levels. Our results lend strong support to numerical models addressing the physical processes underlying extensional systems. These show that, in the case of slow–ultraslow continental extension and the subsequent formation of slow–ultraslow spreading oceans, porosity and shear-localization bands may develop in a previously unstructured lithosphere, prior to melt infiltration. Our studies on the Erro–Tobbio peridotites allow a model for the inception of continental extension and rifting to drifting of slow–ultraslow spreading oceans to be proposed. We suggest that integrated studies of on-land peridotites, coupled with geophysical–structural results from modern oceans, may provide clues to the geodynamic processes governing continental extension and passive rifting.