Entrainment processes during plume ascent

Basalts from intraplate or hotspot ocean islands are found to have distinct geochemical signatures. In particular, at strong plumes like Hawaii, Iceland or Galapagos, there is evidence for at least three geochemically distinct components. This diversity in composition is generally believed to result from the upwelling plume entraining shallow mantle material during ascent, while potentially also entraining other deep regions of the mantle. In order to understand the geochemical message brought to the surface by plumes, this thesis presents a comprehensive study on the dynamics of plume entrainment using analogue laboratory experiments and 30 numerical modelling, with the focus on the following three questions: • Which regions of the mantle arc most efficiently sampled by mantle plumes? • Is the heterogeneous nature of mantle plumes inherited at the source, or does it develop through entrainment during plume ascent? • How are the plume and plume entrainment affected by mantle discontinuities? The analogue laboratory experiments are conducted using glucose syrup contaminated with glass beads to visualize fluid flow and origin. The plume is initiated by heating from below or by injecting hot uncontaminated syrup. Results from the laboratory experiments indicate the presence of a sheath of mostly unheated ma.t