Investigating the Lid Effect on the Generation of Ocean Island Basalts: 2. Geodynamical Simulations

Abstract

The concept that oceanic lithosphere mechanically limits upwelling and decompression melting of mantle plumes is known as the lid effect and is backed up by observations of ocean island basalt (OIB) geochemistry. Nevertheless, in a recent companion study on OIB geochemistry, several additional factors were identified that further influence OIB compositions including a melt-flux filter, whereby plumes with small melt fluxes progressively fail to be sampled in regions of thicker lithosphere. Here, we use 3-D coupled geochemical-geodynamical simulations of decompression melting in a single-lithology mantle plume to predict basalt trace element concentrations for comparison with observations. In addition to supporting the role of the lid effect and melt-flux filter, our models demonstrate that, if it is possible to extract local melts from across the melting domain without complete homogenization, much of the spread in OIB geochemistry observed at individual ocean islands can be reproduced using a single source lithology. Nevertheless, we also find that an OIB source composed solely of primitive mantle contains insufficient rare earth element enrichment, necessitating a recycled crustal component.