This study is to pursue geochemical studies in two related areas of terrestrial mantle research using neon isotopes as the primary geochemical tracer. The first area concerns the origin of mantle plumes. Neon isotopic heterogeneity among various classes of ocean island basalt (OIB) will be pursued as a means of sampling different reservoirs in the terrestrial mantle. The ultimate goal of the project is to further evaluate the relationship between He and Ne by targeting Icelandic hyaloclastites and sub-aerial lavas, which have amongst the highest 3He/4He values worldwide. The plan is to characterize the neon isotope characteristics of the most primitive mantle, and also, to analyze samples having HIMU-type geochemical characteristics from La Palma (Spain) and Mangaia (Cook Islands) to consider the Ne isotope characteristics of this important mantle end-member. The focus of this part of the study will be to ascertain the extent of involvement of recycled components in the genesis of OIB.
A secondary goal of the project is to consider the extent of volatile recycling via subduction zones. Two subduction zones previously identified by the NSF-sponsored MARGINS initiative (Central America and the Izu-Bonin-Mariana system) will be targeted in order to search for evidence of shallow versus deep contributions to the volatile output via arc volcanism. Relationships between neon isotopes and other indices of mantle- or air-derived contributions (specific isotopes of He and Ar) will be investigated with the aim of quantifying their contributions to the total mass balance. Subduction of noble gases (and other volatiles) has the potential to exert a strong control on the geochemical evolution of the mantle.
The impact of this proposal will be on two areas of research activity at SIO/UCSD. First, it will re-establish a dedicated neon isotope facility whose primary role is training of graduate students and post-doctoral visitors. Second, the neon mass spectrometer (VG5400) is sited in the Fluids and Volatiles Laboratory at SIO. The VG5400 is an important addition to the facility such that students and visitors alike will be exposed to many different facets of noble gas research enhancing their training experience.
