Magmatic Activity and Dynamics of Melt Supply of Volcanic Centers of Ultraslow Spreading Ridges: Hints From Local Earthquake Tomography at the Knipovich Ridge

Abstract

Ultraslow spreading ridges with spreading rates below 20 mm/yr exhibit different characteristics and behavior than any faster spreading ridges (Dick et al., 2003). At ultraslow pace, melt supply is not high enough to sustain a spatially continuous shallow melt reservoir underneath the rift valley and therefore volcanic activity and magmatism do not occur along the entire rift axis. Instead, they are bound to distinct regions along the ridge that receive more melt than the ridge on average does (Cannat et al., 2003;Standish et al., 2008). Those magmatic segments build volcanic centers that are widely spaced, often by several tens of kilometers (Cannat et al., 2003;Curewitz et al., 2010;Standish et al., 2008). Volcanic centers receive enough melt to build volcanic edifices in the rift valley. If the melt supply persists over time, seamount chains or a line of elevations form in spreading direction (Jokat et al., 2003;Mendel et al., 2003) (e.g., Figure 1b). The regions in between volcanic centers are dominated