Extreme Heterogeneity in Mid?Ocean Ridge Mantle Revealed in Lavas From the 8°20?N Near?Axis Seamount Chain

Lavas that have erupted at near-axis seamounts provide windows into mid-ocean ridge mantle heterogeneity and melting systematics which are not easily observed on-axis fast-spreading centers. Beneath ridges, most is obscured as magmas aggregate toward the ridge, where they efficiently mix homogenize during transit within shallow magma chambers prior to eruption. To understand deeper magmatic processes contributing oceanic crustal formation, we examine compositions of lavas along a chain volcanic ridges perpendicular East Pacific Rise. We assess chemistry near-ridge using ?200 km-long ?8°20?N. High-resolution bathymetric maps used with geochemical analyses ?300 basalts evaluate petrogenesis feeding these eruptions. Major trace element concentrations radiogenic isotope ratios highly variable on <1 km scales, reveal continuum depleted, normal, enriched spanning full range seamount in northeast Pacific. There no systematic compositional variability chain. Modeling suggests depleted basalt (DMORB) produced by ?5%–15% (MOR) mantle. Normal (NMORB) form from 5% 15% slightly MOR Enriched (EMORB) <1% 10% >15% 100% The presence all three lava types chain, single closest axis, confirms sub-ridge much more heterogeneous than commonly exists over small spatial scales.