Tectonic role of ophiolite‐bearing terranes in the development of the Southern Apennines orogenic belt

Abstract

ABSTRACTNew data on ophiolite‐bearing terranes of the Liguride Complex, together with some information on the terranes of the Sicilide Complex, result in a better understanding of the role and tectonic significance of these units in the construction of the Southern Apennines orogenic belt. The Liguride Complex is composed of two main tectonic units overlain by a thick turbiditic sequence of Late Oligocene‐Middle Miocene age. The uppermost one (Frido Unit) is a polydeformed and polymetamorphosed sequence, composed of two tectonic subunits of shales and calc‐schists, respectively, containing blocks of ophiolite, garnet gneiss, amphibolites and granitoids. This unit is thrust over the un‐metamorphosed terranes (Calabro–Lucano Flysch Unit) consisting of a broken formation with blocks of Late Jurassic ophiolite and their sedimentary cover, Cretaceous‐Eocene pelagic sediments and Late Oligocene volcaniclastic deposits. The Frido Unit underwent HP/LT metamorphism (P= 8–10 Kb; T= 400–500 °C) resulting in glaucophane and lawsonite assemblages in the ophiolitic rocks and aragonite in the meta‐limestones and calc‐schists, followed by greenschist fades metamorphism (P= 4 Kb; T= 300–350 °C). From a structural point of view units of the Liguride Complex comprise structures developed at different structural levels, indicating progressive non‐coaxial deformation in response to tectonic transport towards the N‐NE. The ophiolite‐bearing terranes of the Liguride Complex can be considered as a remnant of an accretionary complex in which the Calabro Lucano Flysch Unit represents the toe of the wedge where frontal accretion processes occur and the Frido Unit is a deeper portion. Emplacement of the Frido Unit is explained as being due to formation of a deep duplex structure during the early stage of continental collision processes. The polarity of tectonic transport provides new evidence that the Liguride Complex represents a suture zone between the Apulian and the Calabrian blocks. The age of collision appears to be not older than late Oligocene. The allochtonous terranes of the Liguride and Sicilide Complexes, therefore, represent a complete accretionary wedge which records, first, subduction of the Neotethys ocean beneath the Calabrian (Europe) continental margin and, later, continental collision with the African block.