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

作者：Molly Anderson, V. D. Wanless, M. R. Perfit, Ethan Conrad, P. M. Gregg, Daniel J. Fornari, W. I. Ridley · 发表于：Geochemistry Geophysics Geosystems · 年份：2020 · DOI：10.1029/2020gc009322 · 被引用次数：25 · 研究领域：Geological and Geochemical Analysis、High-pressure geophysics and materials、earthquake and tectonic studies

Abstract 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 at fast‐spreading centers. Beneath ridges, most heterogeneity is obscured as magmas aggregate toward the ridge, where they efficiently mix and homogenize during transit and within shallow magma chambers prior to eruption. To understand the deeper magmatic processes contributing to oceanic crustal formation, we examine the compositions of lavas erupted along a chain of near‐axis seamounts and volcanic ridges perpendicular to the East Pacific Rise. We assess the chemistry of near‐ridge mantle using a ∼200 km‐long chain at ∼8°20′N. High‐resolution bathymetric maps are used with geochemical analyses of ∼300 basalts to evaluate the petrogenesis of lavas and the heterogeneity of mantle feeding these near‐axis eruptions. Major and trace element concentrations and radiogenic isotope ratios are highly variable on <1 km scales, and reveal a continuum of depleted, normal, and enriched basalts spanning the full range of ridge and seamount compositions in the northeast Pacific. There is no systematic compositional variability along the chain. Modeling suggests that depleted mid‐ocean ridge basalt (DMORB) lavas are produced by ∼5%–15% melting of a depleted mid‐ocean ridge (MOR) mantle. Normal mid‐ocean ridge basalts (NMORB) form from 5% to 15% melting of a slightly enriched MOR mantle. Enriched mid‐ocean ridge bas...