D/H ratios of two meteorites (Renazzo CR and Semarkona LL3), which are
known to exhibit the largest departures from the terrestrial hydrogen
isotopic ratios, have been determined with the CRPG Nancy ion micropr
obe. Correlations between the D/H ratios and the chemical compositions
(H2O, K, Si, C/H) of plausible hydrogen carriers were observed. From
these correlations, it is possible to show that, contrary to previous
interpretations, phyllosilicates are the carriers of the deuterium-ric
h hydrogen in Semarkona and Renazzo: 870 X 10(-6) greater than or equa
l to D/H greater than or equal to 670 x 10(-6) (+4600 greater than or
equal to delta D greater than or equal to 3300 parts per thousand) and
greater than or equal to 320 x 10(-6) (delta D greater than or equal
to 1050 parts per thousand), respectively. Hydrogen is also present in
the chondrules of these two deuterium-rich meteorites. The large diff
erences in D/H ratios between matrix (up to 700 X 10(-6), delta D up t
o +3500 parts per thousand) and chondrules (from 120 X 10(-6) (delta D
= -230 parts per thousand) to 230 X 10(-6) (delta D = +475 parts per
thousand)) show that hydrogen in chondrules cannot originate from the
matrix by simple contamination or diffusion processes. The high D/H ra
tios measured in water-bearing minerals could not have been produced t
hermally within a dense solar nebula. Chemical reactions (i.e., involv
ing ions or radicals), taking place in interstellar space or in the ou
ter regions of the nebula at 110-140 K are presently the only conceiva
ble mechanisms capable of yielding such isotopic enrichments. Water in
these meteorites should no longer be considered as a simple product o
f nebular condensation under equilibrium thermodynamic conditions at T
greater than or equal to 160 K.