Multi-Stage Evolution of the Oceanic Lithosphere beneath Heard Island, Southern Indian Ocean.

This article focuses on characterizing the oceanic lithospheric mantle beneath Heard Island, part of the Kerguelen Plateau large igneous province (LIP) in the southern Indian Ocean, through petrographic and geochemical analysis of spinel-bearing harzburgite xenoliths hosted in basanite lavas. The study reveals a complex mantle history involving extensive partial melting (~26–30% melt extraction at 1–3 GPa), sub-solidus re-equilibration reactions producing clinopyroxene and chromian-spinel symplectites, and heterogeneous carbonatite metasomatism that enriched certain clinopyroxene grains in light rare earth elements and other trace elements. Following entrainment as xenoliths in ascending basanite magma, the mantle fragments underwent further modification via melt–rock interaction, notably the partial dissolution of orthopyroxene and formation of new mineral assemblages (wehrlitisation). These findings highlight the importance of distinguishing in situ mantle processes from alterations occurring during xenolith transport to better understand the composition and evolution of the lithospheric mantle beneath the Kerguelen Plateau.