Oceanic core complex

[2] Since then numerous such structures have been identified primarily in oceanic lithosphere formed at intermediate, slow- and ultra-slow spreading mid-ocean ridges, as well as back-arc basins.

[6] Some of these structures have been drilled and sampled, showing that the footwall can be composed of both mafic plutonic and ultramafic rocks (gabbro and peridotite primarily, in addition to diabase), and a thin shear zone that includes hydrous phyllosilicates.

The core complex builds on the uplifted side of the fault, where most of the gabbroic (or crustal) material is stripped away to expose mantle rocks at the seabed.

Analog models of subduction show that density contrast of more than 200 kg/m3 between two juxtaposed lithospheric slabs would result in the underthrusting of the denser one to a depth of about 50 km, where phase transformation causes remineralization of pyroxenes into garnets.

[8][full citation needed] There is ground to presume that at slow ridge and fracture zone intersections, the density contrast of the juxtaposed slabs would exceed 200 kg/m3, the friction between the slabs would be low, the thermal gradient would be about 100 C/km, and with about 5% water content, the drop of the solidus (a boundary transition on a phase diagram) of basalt at relatively low pressure would enable the co-occurrence of serpentinites and peridotites, the abundant rock-types in oceanic core complexes.