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'' between 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 and Triassic times and will contribute to the closure of
the Paleozoic oceans.