David Hilton, Ph.D.

scripps institution of oceanography

I have worked extensively on convergent margin volcanism (in Indonesia, the Andes, and the Lesser Antilles) with particular emphasis on the nature of the subducting slab and the provenance of volatiles from arc-related volcanoes. Initial work in Indonesia (with Harmon Craig) showed the spectacular sensitivity of helium isotopes to the mapping of compositional changes in the subducting slab - from oceanic to continental margin affinity - at the juncture of the Sunda and Banda arcs. This was followed-up by a study directed at explaining the apparent 'decoupling' of helium and strontium isotopes across this particular region, and pinpointing subducted continental margin and not subducted sediments as the source of the radiogenic helium emitted along the arc. Further studies in Indonesia have considered the problems of distinguishing 'crustal' signatures from the slab versus upper-level contamination effects (a topic clearly of relevance to the debate over Heard Island and low-3He hotspots).

Research projects in the Andes and Lesser Antilles were undertaken specifically to consider the respective effects of thickened crust and sediment variations on the volatile characteristics of convergent margin volcanism. It was concluded that eruption of magmas through thickened continental crust could have a major effect on the volatile systematics, and that in many instances helium could trace the effects of assimilation/contamination processes far more sensitively than other geochemical indicators. Current work in the Lesser Antilles is aimed at evaluating the effects of changes in sediment composition (on the down-going slab) on the CO2 flux of arc volcanoes. The theme common to both studies is understanding the volatile mass balance of the subduction process.