Rifting processes, leading to sea-floor spreading, are characterized by a sequence of events: transtensive phase of extension with syn-rift volcanism; simple shear extension accompanied by lithospheric thinning and asthenospheric... more
Rifting processes, leading to sea-floor spreading, are characterized by a sequence of events: transtensive phase of extension
with syn-rift volcanism; simple shear extension accompanied by lithospheric thinning and asthenospheric up-welling and
thermal uplift of the rift shoulder and asymmetric volcanism. The simple shear model of extension leads to an asymmetric
model of passive margin: a lower plate tilted block margin and an upper plate flexural, ramp-like margin. Both will be affected
by thermal contraction and subsidence, starting soon after sea-floor spreading.
Based on these actualistic models Tethyan margins are classified as one type or the other. Their evolution from the first
transtensional phase of extension to the passive margin stage are analyzed. Four main rifting events are recognized in the
Tethyan realm: an episode of lower Paleozoic events leading to the formation of the Paleotethys; a Late Paleozoic event leading
to the opening of the Permotethys and East Mediterranean basin; an early Mesozoic event leading to the opening of the Pindos
Neotethys and a Jurassic event related to the opening of the Alpine/Atlantic Neotethys.
Type margins are given as example of each rifting event:
-Northern Iran (Alborz) as a type area for the Late Ordovician to Silurian rifting of Paleotethys.
- Northern India and Oman for the Late Carboniferous to early Permian rifting of Permotethys.
- The East Mediterranean (Levant, Tunisia) as a Late Carboniferous rifting event.
- The Neotethyan rifting phases are separated in two types: an eastern Pindos system found in Turkey and Greece is
genetically linked to the Permotethys with a sea-floor spreading delayed until middle Triassic; a western Alpine system directly
linked to the ·opening of the central Atlantic is characterized by a Late Triassic transtensive phase, an early to Middle Liassic
break-away phase and, following sea-floor spreading, a thermal subsidence phase starting in Dogger.
Problems related to the closure of the Paleozoic oceanic domains are reviewed. A Late Permian, early Triassic phase of
"docking" bet~~~n an European accretionary prism (Chios) and a Paleotethyan margin is supported by recent findings in the
Mediterranean area. Back-arc rifting within the European active margin led to the formation of marginal seas during Permian
anq Triassic times and will contriqute to the closure of the Paleozoic oceans.
