Summary: The Laurens Peninsula Series (LPS) lavas of Heard Island are unique among ocean island suites in having extremely high TiO₂ (>4.5%) and high P₂O₅ (>1%) abundances in basanitic compositions. These chemical features are reflected in both their petrography and in the composition of calculated primary magmas, and lead to a suggested origin for the LPS source either as ‘fossil’ plume melt frozen within the lithospheric mantle or as continental lithospheric mantle detached during the break-up of Australia and Antarctica and incorporated into the Kergeulen Plateau.