The hydrogen isotopic composition and water content of southern Pacific MORB: A reassessment of the D/H ratio of the depleted mantle reservoir

In this paper, we re-investigate the isotopic composition of hydrogen in MORB and the possible effects of contamination on delta D and water content. A suite of 40 N-MORB from the Pacific-Antarctic ridge, far from any hotspot, was analyzed for chlorine content by electron microprobe and for water content and delta D with silica tubes. Cl concentrations (from 29 to 2400 ppm) indicate widespread contamination, more intense with faster spreading rates, while water contents (from 840 to 7800 ppm) are mainly controlled by igneous processes. delta D values range from -76 to -48 parts per thousand, with an average value of -61 parts per thousand. The lack of correlation between Cl content and either H2O/Ce or SD indicate that contamination has a negligible effect on delta D for our samples, which is therefore characteristic of the mantle below the Pacific-Antarctic ridge. We suggest that the 20 parts per thousand lower delta D value reported for the North Pacific and North Atlantic is highly unlikely from geodynamical arguments. We propose that the convecting mantle is characterized by a delta D of -60+/-5 parts per thousand, as supported by the most recent data from North Atlantic N-MORB. (C) 2013 Elsevier B.V. All rights reserved.