The southern ridge axis impacting the Andrew Bain Fracture Zone is formed by two overlapping ridges. Two dredges were carried out in the westernmost of the two overlapping segments. S2318 is located in the small deep western axial basin and S2319 in the central large axial basin. Dredge S2317 is located on the flank of a conic structure which suggests recent volcanic activity. Numerous fragments of pillow basalts have been recovered together with minor gabbros and one mantle peridotite. Basalts belong at least to two different time events. One population of basalts is fresh, covered by thick glassy crust, probably a recent event. The other one appears more altered, coated by Fe-Mn and characterized by a marked vesicularity, probably an older event. Both populations are aphyric, with rare plagioclase feno- or megacrysts. The small Pl-Cpx gabbroic samples show a variable grain size but overall they are strongly altered. One small fragment of granular serpentinized peridotite has been also recovered together with a small fragment of breccia cemented by Fe-Mn mineralization. Dredge S2318 comprises gabbros and mantle peridotites in equal proportions plus minor dunites and breccias. Gabbros have variable grain size from micro to pegmatitic. Compositionally they vary from troctolitic to olivine-bearing gabbro, gabbro, leucogabbro and oxide-bearing gabbro. Mantle peridotites have granular to porphyroclastic to mylonitic textures. They vary from harzburgitic to lherzolitic terms, deeply serpentinized, with strong modal variability in orthopyroxene content. Clinopyroxene grains usually have a marked lineation crosscutting the rock foliation. They are associated with spinel and rarely with plagioclase grains. All peridotites show a weak to well developed high-T foliation marked by opx. Mylonites of both harzburgite and lherzolites terms, are also present. Dunites are completely serpentinized, cut by thin spinel chains. An oficalcitic breccia with dunitic clasts is cemented by carbonatic ooze.
Dredging attempts of the eastern overlapping segment have provided only few erratic samples. This ridge segment is covered by a thick layer of sediments with apparently no recent magmatic activity. Only one peridotitic mylonite has been recovered on the nodal basin wall at the eastern RTI.