Evolution of the Red Sea/Gulf of Suez and the Central Atlantic rift
systems shows that an initial, transtensive rifting phase, affecting a
broad area around the future zone of crustal separation, was followed by
a pre-oceanic rifting phase during which extensional strain was
concentrated on the axial rift zone. This caused lateral graben systems
to become inactive and they evolved into rift-rim basins. The
transtensive phase of diffuse crustal extension is recognized in many
intra-continental rifts. If controlling stress systems relax, these
rifts abort and develop into palaeorifts. If controlling stress systems
persist, transtensive rift systems can enter the pre-oceanic rifting
stage, during which the rift zone narrows and becomes asymmetric as a
consequence of simple-shear deformation at shallow crustal levels and
pure shear deformation at lower crustal and mantle-lithospheric levels.
Preceding crustal separation, extensional denudation of the lithospheric
mantle is possible. Progressive lithospheric attenuation entails
updoming of the asthenosphere and thermal doming of the rift shoulders.
Their uplift provides a major clastic source for the rift basins and the
lateral rift-rim basins. Their stratigraphic record provides a sensitive
tool for dating the rift shoulder uplift. Asymmetric rifting leads to
the formation of asymmetric continental margins, corresponding in a
simple-shear model to an upper plate and a conjugate lower plate margin,
as seen in the Central Atlantic passive margins of the United States and
Morocco. This rifting model can be successfully applied to the analysis
of the Alpine Tethys palaeo-margins (such as Rif and the Western Alps).