Basal lithospheric detachment, eastward mantle flow and mediterranean geodynamics: A discussion

Abstract

W-dipping and W-facing frontal subductions as well as oblique subductions are distinguished in the Mediterranean. W-dipping subductions (i.e. the Apennines, Carpathians) are characterized by high dip of the slab, small elevation of the chain, deep foreland basin filled in situ by the eroded chain. E-dipping subductions (i.e. the W-Alps, Dinarides) have minor dip of the slab, greater elevation, shallow foreland basin. Lateral subductions show transitional characters. Surficial decouplage between the lithosphere and asthenosphere in conjunction with an eastward and northeastward directed mantle flow are interpreted as first order phenomena in controlling Mediterranean geodynamics. Mantellic thermal anisotropies control the amount of decoupling between the lithosphere and the asthenosphere, but lateral anisotropies between continental and oceanic lithospheres are also considered here as primary factors generating variations in velocity among plates. This eastward (and northeast) mantle flow can account for the main tectonic directions of compression or extension E-W or NE-SW oriented (W-Alps, Apennines, West European rift system, Dinarides, Central Carpathians, Hellenides, Cyprus subduction, etc.) as well as the eastward migration of the Neogene rifts and magmatism in the central western Mediterranean (Provençal and Algerian Basins, Tyrrhenian Sea). The main tectonic regime is considered to be more E-W rather than N-S. This trend fits very well with the global pattern of plate motions. In another way, the numerous extensional basins with very high heat flow, and sometimes oceanization, are difficult to explain in the classical scheme of N-S compression. N-S compressions are interpreted as body forces along transpressive belts (i.e. Maghrebides, Sicily, central eastern Alps, southern Carpathians) or due to localized regional rotations (i.e. the Pyrenees). In addition, the Aegean Sea is considered as a region of sinistral transtensive stretching due to a larger coupling of the Turkey lithosphere relative to its underlying mantle compared to the coupling of the Hellenides.