Programme des sessions > Par intervenant > Lesourd--Laux Thomas

The kinematics of the rifting and initial oceanic opening of the Equatorial Atlantic ocean has
almost been a blind spot in the reconstruction of the separation of Africa from America. It can
likely be attributed to the absence of magnetic anomalies and the disruption of the fracture zones
by both the volcanism and the Caribbean subduction. The only study devoted to this subject is
the unpublished PhD of Campan(1995), whose results were since incorporated in all
reconstructions, We propose a new kinematic reconstruction focused on the early rifting of the Equatorial Atlantic that relies on:

-Detailed mapping of the fracture zones at the connection between the Equatorial and the Central
Atlantic and more specifically the interpretation of the Cretaceous-Jurassic Line (CJL). The CJL
is the boundary between the Cretaceous oceanic crust formed in the Equatorial Atlantic and the
Jurassic oceanic crust previously formed in the Central Atlantic. We have mapped the CJL on
the north of the Demerara plateau as well as on the south-west of the Guinea plateau. The two
parts of the CJL formed as a single structure that we interpret as a tranform fault related to a
first stage of opening. According to these observations, the CJL corresponds to the direction of
the early opening of the Equatorial Atlantic.

-And a new interpretation of seismic profiles from the margins of the Equatorial Atlantic together
with geological observations (e.g. Soares Junior et al., 2011) that suggest two distinct rift
phases during the lower Cretaceous. An older northern rift propagated from the Central Atlantic
towards the South East to reach the present-day mouth of the Amazon River, and a southern rift
propagated westward from the northern edge of the South Atlantic. Once these two rifts were
connected, the kinematics of the South Atlantic prevailed and lead to a kinematic change between
the Amazon mouth and the Central Atlantic. These two rifts phases can be accounted introducing
intraplate deformation localized in the Amazon basin.

This new model of the Equatorial Atlantic rifting better respects the morphologies of the margins
and the existing fracture zones, without generating large-scale intra-plate movements.