Petrogenesis of shield volcanism from the Juan Fernández Ridge, Southeast Pacific: Melting of a low-temperature pyroxenite-bearing mantle plume

Abstract

© 2019 Elsevier LtdThe Juan Fernández Ridge (JFR) is an age-progressive volcanic chain (∼800 km long) related to a fixed mantle plume in the Southeast Pacific offshore central Chile. The high 3He/4He ratio (up to 18 times higher than that of the atmosphere) and spatiotemporal 40Ar/39Ar geochronology suggest that the source material of the JFR is derived from the lower mantle and transferred to the surface by a relatively stationary plume. We used new whole-rock geochemical data (major-element, trace-element, and Sr–Nd–Pb isotopic data) for representative samples from the shield-stage of volcanism in the JFR (from O'Higgins Guyot, Alpha Seamount, Robinson Crusoe Island, and Alejandro Selkirk Island) to develop a petrogenetic model with the goal of understanding the temporal and spatial evolution of magmatism along the JFR. The shield-building lavas of JFR consist primarily of tholeiitic to alkalic basalts. Their compositional differences are explained by the fractional crystallization o