Genesis of primitive Hawaiian rejuvenated-stage lavas: Evidence for carbonatite metasomatism and implications for ancient eclogite source

TL;DR

This study investigates Hawaiian primitive lavas to reveal that their unique compositions result from carbonatite metasomatism of deep mantle sources, with implications for understanding mantle processes and ancient subduction events.

Contribution

It provides evidence that Hawaiian rejuvenated-stage lavas originate from a carbonatite metasomatized eclogite mantle source, a novel insight into mantle heterogeneity and melt generation.

Findings

Hawaiian lavas show signatures of carbonatite metasomatism.

Salt Lake Crater xenoliths derive from deep eclogite sources.

Hf isotope systematics indicate ancient metasomatic events.

Abstract

To constrain a contribution of deep carbonated mantle, to fractionation of Hf relative to rare earth elements (REE) in volcanic series, we examine available high-quality data on major, trace element and Nd-Hf isotope compositions of primitive lavas and glasses erupted during preshield, postshield and mostly rejuvenated stage of the Hawaiian hot spot (Pacific Ocean). Strong variations of Hf/Sm, Zr/Sm, Ti/Eu, K/Th, Nb/Th, La/K and Ba/K in the lavas are not features of the melt equilibration with residual amphibole or phlogopite, and cannot be due to variable degrees of batch or dynamic melting of uncarbonated lherzolite source. Enrichment in REE, Th and Ba relative to K, Hf, Zr, Ti and Nb together and low Si, high Na, K and Ca contents in the Hawaiian lavas are compositional features of carbonated mantle lithospheric to asthenospheric peridotite source affected by carbonatite metasomatism. In contrast, major and trace element signatures of most primitive preshield- and postshield-stage magmas require pyroxenite source. The available data infer that Salt Lake Crater garnet pyroxenite xenoliths hosted by the Koolau volcano lavas on Oahu, Hawaii, were derived from deep eclogite source likely generating the carbonatite melts within the Hawaiian plume. Highly radiogenic Hf and decoupled Nd-Hf isotope systematics recorded in the Salt Lake Crater mantle xenolith series on Oahu may be explained by strong Hf fractionation relative to REE owing to ancient event of carbonatite metasomatism, which is likely related to partial melting of the deeply subducted carbonated eclogite within the Hawaiian plume.