48
C. Variations of Stable Isotope Ratios in Nature
IsOrO data for meteorites have been published by SILVERMAN
(1951), VINOGRADOV et al. (1960), REUTER et al. (1965), TAYLOR et al.
(1965), and ONUMA et al. (1972a, b).
On the basis of isotopic analyses of separated minerals, TAYLOR et
al. (1965) were able to divide the stony meteorites into 3 groups.
1) basaltic achondrites, hypersthene achondrites, and mesosiderites
with pyroxene b-values from 3.7 to 4.4%0;
2) high-iron group and low-iron group chondrites, enstatite chondrites, enstatite achondrites with pyroxene b-values from 5.3 to 6.3%0;
3) carbonaceous chondrites with a highly variable oxygen isotope
composition, implying that these chondrites are much less equilibrated
than ordinary chondrites.
ONUMA et al. (1972a) assumed that the b l8 0-values of coexisting
minerals (plagioclase, pyroxene, olivine) from ordinary chondrites were
crystallized in oxygen isotope equilibrium. They estimated the maximum
temperature attained during thermal metamorphism to be 950 ± 100° c.
BOATO (1954) analyzed the deuterium-to-hydrogen ratio, DjH, of the
water extracted at 180° C from carbonaceous chondrites, which falls in
the range of terrestrial variations. The water obtained at higher temperatures has a much greater variation range, and in four cases is outside the
terrestrial range. Corrected bD-values vary between - 154 and + 270%0.
A discussion on the controversial meaning of the deuterium distribution
in meteorites was later published by EDWARDS (1955) and BOATO (1956).
Carbon and sulfur are common constituents of many meteorites.
They can be found in a number of minerals, and they sometimes occur in
various valence states in one meteorite specimen. Carbon and sulfur isotope determinations on meteorite specimens were initiated to answer the
following questions:
1) What evidence exists that isotopic variations have occurred during
nucleosynthesis? 2) Do large fractionations exist similar to those found
on earth? 3) Is there a trend in the fractionation pattern which might
indicate biological activity?
Meteoritic sulfur usually has a rather constant b 34 S-composition
(MACNAMARA and THODE, 1950; VINOGRADOV et aI., 1957; AULT and
KULP, 1959; THODE et al., 1961; JENSEN and NAKAI, 1962; HULSTON and
THODE, 1965; MONSTER et aI., 1965; KAPLAN and HULSTON, 1966).
Troilite is the most abundant sulfur compound of iron meteorites
and shows b 34 S-values from 0 to 0.6%0 relative to Canyon Diablo troilite
(KAPLAN and HULSTON, 1966). Stony meteorites also contain a wide
variety of sulfur compounds. MONSTER et al. (1965) and KAPLAN and
HULSTON (1966) separated the various sulfur constituents. The results
are summarized in Table 8.
C. Variations of Stable Isotope Ratios in Nature
IsOrO data for meteorites have been published by SILVERMAN
(1951), VINOGRADOV et al. (1960), REUTER et al. (1965), TAYLOR et al.
(1965), and ONUMA et al. (1972a, b).
On the basis of isotopic analyses of separated minerals, TAYLOR et
al. (1965) were able to divide the stony meteorites into 3 groups.
1) basaltic achondrites, hypersthene achondrites, and mesosiderites
with pyroxene b-values from 3.7 to 4.4%0;
2) high-iron group and low-iron group chondrites, enstatite chondrites, enstatite achondrites with pyroxene b-values from 5.3 to 6.3%0;
3) carbonaceous chondrites with a highly variable oxygen isotope
composition, implying that these chondrites are much less equilibrated
than ordinary chondrites.
ONUMA et al. (1972a) assumed that the b l8 0-values of coexisting
minerals (plagioclase, pyroxene, olivine) from ordinary chondrites were
crystallized in oxygen isotope equilibrium. They estimated the maximum
temperature attained during thermal metamorphism to be 950 ± 100° c.
BOATO (1954) analyzed the deuterium-to-hydrogen ratio, DjH, of the
water extracted at 180° C from carbonaceous chondrites, which falls in
the range of terrestrial variations. The water obtained at higher temperatures has a much greater variation range, and in four cases is outside the
terrestrial range. Corrected bD-values vary between - 154 and + 270%0.
A discussion on the controversial meaning of the deuterium distribution
in meteorites was later published by EDWARDS (1955) and BOATO (1956).
Carbon and sulfur are common constituents of many meteorites.
They can be found in a number of minerals, and they sometimes occur in
various valence states in one meteorite specimen. Carbon and sulfur isotope determinations on meteorite specimens were initiated to answer the
following questions:
1) What evidence exists that isotopic variations have occurred during
nucleosynthesis? 2) Do large fractionations exist similar to those found
on earth? 3) Is there a trend in the fractionation pattern which might
indicate biological activity?
Meteoritic sulfur usually has a rather constant b 34 S-composition
(MACNAMARA and THODE, 1950; VINOGRADOV et aI., 1957; AULT and
KULP, 1959; THODE et al., 1961; JENSEN and NAKAI, 1962; HULSTON and
THODE, 1965; MONSTER et aI., 1965; KAPLAN and HULSTON, 1966).
Troilite is the most abundant sulfur compound of iron meteorites
and shows b 34 S-values from 0 to 0.6%0 relative to Canyon Diablo troilite
(KAPLAN and HULSTON, 1966). Stony meteorites also contain a wide
variety of sulfur compounds. MONSTER et al. (1965) and KAPLAN and
HULSTON (1966) separated the various sulfur constituents. The results
are summarized in Table 8.