Light stable isotopic compositions of enriched mantle sources: Resolving the dehydration paradox

Volatile compositions of enriched mid-ocean ridge basalt are presented, including water concentrations (FTIR and TC/EA) and isotopic ratios of hydrogen (Conventional and TC/EA), boron (laser ablation ICP-MS), lithium (MC-ICP-MS) and oxygen (laser fluorination). Of special significance, we performed an interlaboratory comparison between conventional and TC/EA techniques for hydrogen isotopic ratios in basaltic glasses, resulting in revisions to the mica standardization protocol for the TC/EA method. Glasses from the Arctic and South Atlantic were analyzed for deltaD SMOW using stepped-heating manometry/mass spectrometry at the University of Miami Stable Isotope Laboratory. Water contents and hydrogen isotope ratios of glasses from the Azores Platform and EPR 6° to 17°N were measured by continuous flow via the High Temperature Conversion / Elemental Analyzer (TC/EA) technique at the University of Oregon. In situ boron isotopic compositions were measured by laser ablation, multiple-multiplier ICP-MS at the Department of Terrestrial Magnetism, Carnegie Institute of Washington. Lithium concentrations and isotopic compositions were measured by MC-ICP-MS at Lamont-Doherty Earth Observatory using chemistry and column procedures following Tomascak et al. [1999], with minor modifications. Oxygen isotopes from Arctic ridge samples were measured by J. Eiler at the California Institute of Technology as described in Cooper et al. [2004].