Back-arc dynamics controlled by slab rollback and tearing: a reappraisal
of seafloor spreading and kinematic evolution of the Eastern Algerian
basin (western Mediterranean) in Middle-Late Miocene
Abstract
In spite of clear fan-shaped magnetic anomalies in the Eastern Algerian
Basin (EAB), the way how and the time when seafloor spreading occurred
are still debated. In this work, a new seismo-stratigraphic
interpretation based on deep-penetration reflection seismic data
correlated to reduced-to-the-pole magnetic anomalies and to
onshore-offshore litho-stratigraphic correlation of Pre-Messinian units
bring new constraints on its age and mode of opening. Our results reveal
that the seafloor spreading of EAB occurred with a intermediate to fast
half-spreading rate of 3.7±0.5 cm/yr during 2.45±0.18 Myr in
Langhian-Serravalian times, i.e. after the Corsica-Sardinia block
rotation and the collision of Lesser Kabylia with Africa. We revise the
kinematics of the Algero-Balearic domain into three stages: (1) birth of
a highly stretched continental basin accommodating the southern drift of
the Kabylies driven by Tethyan slab rollback between ~23
and ~15 Ma, (2) fast opening of a new basin (EAB)
between 15.2 and 12.7 Ma by clockwise rotation of a Greater Alboran
Block (GALB), and (3) continuation of westward translation of the GALB.
The last stages match both the late formation of Subduction-Transform
Edge Propagator (STEP) faults at the toes of the Algero-Balearic margins
and the post-collisional volcanic migration along the Algerian margin
interpreted as related to slab break-off. This new scheme invalidates
most previous opening models of the Algero-Balearic basin and favors a
significant stretching and splitting of the GALB into several
continental fragments resulting from the westward propagation of the
arcuate subduction front by lateral tearing of a narrow slab.