Rapid uplift of a lithospheric Sliver Near the Vema FZ (Central Atlantic) due to change in the pole of rotation

The Vema F.Z. offsets the Mid Atlantic Ridge by about 320 km at 10ø45' N. The southern flank of the transform valley is bounded by a prominent transverse ridge (VTR), reaching a minimum depth of ~500 m. Several lines of evidence indicate that the north facing wall of the VTR exposes a complete, relatively undisturbed section of uplifted oceanic lithosphere. The length of the VTR is ~300 km, similar to the length of offset of the transform. The VTR starts abruptly about 140 km from the MAR axis, in crust roughly 10 m.y. old, assuming an half spreading rate of 1.5 cm/y. This age marks the end of the uplift phase of the VTR. The time of initiation of uplift is marked probably by an abrupt change of orientation of sea floor morphostructural fabric, from parallel to the present ridge axis to ~5§ to 10§ oblique. This change of orientation took place about 12 Ma, and is related to a change in the position of the pole of rotation that caused extension across the transform and triggered flexure of a lithospheric slab and uplift of the transverse ridge. The ~4 km uplift of the VTR took place in roughly 2 m.y. with an average rate of uplift of 2 mm/y. Uplift rates appear to have been similar throughout the 300 km length of the VTR. The flexure and rapid uplift did not cause major internal deformation of the lithospheric slab.