Large-scale sedimentary recycling of tectonic melange in a forearc setting: The Ionian basin (Oligocene-Quaternary, southern Italy)

Distinctive horizons of melange-ranging in maximum thickness from a few tens to several hundreds of meters-are conformably interbedded with the regularly stratified, Oligocene-to-Quaternary, predominantly marine deposits of the Ionian forearc basin along the leading edge of the Calabria-Peloritani microplate of southern Italy. These melange horizons were emplaced from the late-early to the late Miocene during collision of the southern and northern margins of the microplate with the passive margins of northern Africa and the Apulian Platform, respectively. Collisional deformation induced uplift of parts of the accretionary prism and ensuing sedimentary recycling of melange into the adjacent Ionian forearc basin. The thickest melange horizon can be traced for a distance >80 km with a consistent stratigraphic position within the forearc basin fill, and ranges in thickness from similar to 1 km near the collision zone to zero away from it. It was emplaced in the late Burdigalian and records oblique collision of the Calabria-Peloritani microplate with the northern continental margin of Africa. In this context, portions of the melange of the accretionary prism were extruded tectonically and gravitationally mobilized from southwest to northeast in the remaining, undeformed parts of the forearc basin. This interpretation is supported by (1) the overall geometry of the melange horizon pinching out away from the collision zone, (2) its conformable contacts and chronostratigraphic relationships with the underlying and overlying stratigraphic units, (3) its composition, and (4) the absence of tectonic deformation at base and top of the horizon. Younger and thinner melange horizons are interbedded within the latest Tortonian-Messinian succession and resulted from the erosion of thrust tip areas within the inner portion of the accretionary prism following incipient collision of the northern end of the microplate with the Apulian Platform. Integration of the results of this and other studies indicate that sedimentary recycling of large volumes of melange from accretionary prisms into forearc basins is an important process along both collisional and noncollisional active plate margins.