This is a study of the petrology and geochemistry of the 1st systematic samples representing the plutonic foundation of a slow-spreading mid-ocean ridge. The rocks are from a 20 by 35 km ~3.7 million year old core complex corresponding to the 2nd order ridge segment south of the Kane Fracture Zone. An ODP Site Survey with Seabeam, deep-tow magnetics and bathymetry, dredging and the Jason ROV mapped it in fall 2004. 2667 kg of rock were sampled. Rocks outcrop systematically over the complex, with dunite and troctolite indicating a ~10 km wide focused mantle melt flow zone that fed an ancient southern volcanic center. The scarcity of these rocks to the north indicates that the overlying diabase and pillow basalt likely represent down-axis fissure eruptions from the southern magmatic center. These observations match the volcanic carapace on the opposing tectonic plate, where an axial volcanic high corresponds to the position of the magma center. The samples will allow the study of melt generation and crustal accretion beneath an end-member "normal" Mid-Atlantic Ridge spreading segment for the first time. They can constrain the melting process, and allow comparison of peridotite compositions from a normal ridge-melting environment to those representing extreme low-degrees of melting at the Gakkel Ridge that may lie close to the MORB mantle source composition.
