While occurring at relatively amagmatic spreading centres, the footwalls of these detachment faults are much more influenced by magmatism than in continental settings. In fact, they are often created by ‘continuous casting’: new footwall is continually being generated by mantle or melt from a magma chamber as slip occurs on the fault.[1] The lithology is dominated by gabbro and peridotite, resulting in a mineralogy of olivine, serpentine, talc and plagioclase. This is in contrast to continental settings, where the mineralogy is dominantly quartz and feldspar.