Romanche Trench

The trench has been formed by the actions of the Romanche Fracture Zone, a portion of which is an active transform boundary offsetting sections of the Mid-Atlantic Ridge.

[1] It was named after the French navy ship La Romanche, commanded by captain Louis-Ferdinand Martial which on 11 October 1883 made soundings that revealed the trench.

North of and parallel to the fracture zone is a transverse ridge which is particularly prominent over hundreds of kilometers east and west of the MAB of the South Atlantic.

The summit of the transverse ridge is capped by Miocene shallow-water limestones that reached above sea level 20 Ma before subsiding abnormally fast.

[4] The transverse ridge separates the present trench from an 800 km (500 mi)-long aseismic valley where the Romanche transform was located until about 10–8 Ma.

The Romanche and Chain Fracture Zones create a huge gap in the MAR and can act as a "Subsea Berlin Wall" segregating the North Atlantic communities from those in other oceans.