Active Long-Lived Faults Emerging Along Slow-Spreading Mid-Ocean Ridges

In the classic mid-ocean ridge model, new seafloor is generated through a combination of magmatic diking feeding lava flows at the spreading axis, and the formation of short-offset, high-angle normal faults that dip toward the axis. These processes lead to the formation of a layered magmatic crust and linear, ridge-parallel abyssal hills on both ridge flanks. This model of ocean crust generation applies well to fast-spreading mid-ocean ridges (i.e., > 80 mm yr–1), but it is not always valid at slower-spreading ridges. Instead, at slow-spreading ridges such as the Mid-Atlantic Ridge (MAR), which is opening at about 25 mm yr–1, the formation of long-lived faults (called detachments) on one flank of the ridge axis is an important process in seafloor formation (Cann et al., 1997; Karson, 1999; MacLeod et al., 2009; Schroeder et al., 2007; Smith et al., 2008; Tucholke et al., 1998). In fact, active detachment faults have been identified along nearly half of the MAR axis between 12° and 35°N (Escartín et al., 2008).