Fine-scale segmentation of the crustal magma reservoir beneath the East Pacific Rise

The global mid-ocean ridge is segmented in its seafloor morphology and magmatic systems, but the origin of and relationships between this tectonic and magmatic segmentation are poorly understood(1-5). At fast-spreading ridges, tectonic segmentation is observed on a fine scale(2,4,6-8), but it is unclear whether this partitioning also occurs in the magmatic system. Fine-scale tectonic segmentation could have a deep origin, arising from the distribution of upwelling mantle melt, or a shallow origin, linked to offset intruding dikes from long, more continuous crustal reservoirs(2,9). Here we use seismic reflection data from the fast-spreading East Pacific Rise, between 8 ffi 20 degrees N and 10 ffi 10 degrees N, which includes a unique area where two documented volcanic eruptions have occurred(10-15), to image the crustal magma bodies in high resolution. We find that the magma reservoirs form 5-to 15-km-long segment s that coincide with the fine-scale tectonic segmentation at the seafloor and that three lens segments fed the recent eruptions. Transitions in composition, volume and morphology of erupted lavas coincide with disruptions in the lens that define magmatic segments. We conclude that eruptions at the East Pacific Rise are associated with the vertical ascent of magma from lenses that are mostly physically isolated, leading to the eruption of distinct lavas at the surface that coincide with fine-scale tectonic segmentation.