Isotopic analysis of water released
by vacuum heating of hydrous minerals and sub-marine
basaltic glasses indicates that they vary in δD_(SMOW)
between ca. +10 and -115 per mil (e.g., [1]). However,
with few exceptions variations within that range are not
well correlated with other geochemical and geologic
properties and it is debated whether they reflect isotopic
heterogeneity in the mantle, fractionations produced
during ascent to the surface, or sub-solidus alteration.
This ambiguity is at least partly due to the
large sample size and slow rate of conventional analyses,
which precludes linking isotopic ranges to grain-scale
petrographic variables or constructing large data
bases (many 10’s of samples) in a reasonable period of
time. Ion microprobe methods provide one solution to
these problems, although they suffer from analytical
uncertainties nominally 5 to 10 times worse than conventional
measurements and large fractionations that
can be a source of systematic error
