Temporal variation in spreading processes at the Eastern Romanche-Mid-Atlantic Ridge intersection

We studied the east intersection between the Romanche transform fault (TF) and the Mid-Atlantic ridge using bathymetry and gravity anomalies, to investigate the temporal evolution of the ultra-cold ridge-transform intersection. Our results reveal a complex ridge axis, with evidence of a significant decrease in the along-axis melt supply towards the RTI but also since ~10 Ma.

Over a 100 km distance south of the RTI, the ridge axis is formed by three spreading segments offset by large non-transform discontinuities. Large detachment faults mark the present-day spreading style at the RTI, while magma supply increases away from the Romanche intersection. Axial and near-axis fault patterns reveal a marked obliquity, especially in the north and center of the study area.In lithosphere older than 10 Ma, the ridge axis appears to form a single spreading segment between the Romanche and Chain TFs, perpendicular to the spreading direction, with relatively regular abyssal hills. From around 10 to 3 Ma, oceanic core complexes (OCCs) developed in the northern part of the ridge axis south of the Romanche TF.  The complexity of the ridge axis appears to have increased in the last 3 Ma, with ridge obliquity accompanying axial instabilities and ridge jumps.  At least three eastward ridge relocations were identified immediately south of the Romanche TF, rupturing a series of OCCs located in the African plate, east of the ridge axis. This pattern could reflect a progressive decrease in the melt supply, in particular since 3-5 Ma. This may be related to a significant reduction of the ridge spreading rate as seen from kinematic models which allowed the cooling effect of the large offset Romanche TF to dominate the spreading processes in the area.