32
B. Fractionation Mechanisms of Selected Elements
two-directional exchange method at temperatures above 350
0
C to obtain an alkali-feldspar-water calibration curve. O'NEIL and TAYLOR
(1966) also used the alkali ion exchange technique to obtain the muscovite-water calibration curve. These experiments were made by transforming kaolinite or paragonite to muscovite, and in both instances complete
oxygen isotope exchange accompanies the cation exchange.
The most suitable and sensitive mineral pair is the magnetite-quartz
pair. BERTENRATH et al. (1972) have redetermined the magnetite-water
curve, revising the curve given by O'NEIL and CLAYTON (1964).
Some of the experimentally determined calibration curves are shown
in Fig. 11.
b) Fractionations Due to Kinetic Processes
Oxygen isotope fractionations occurring during photosynthesis
(DOLE and JENKS, 1944) and respiration (LANE and DOLE, 1956) are
kinetic processes. MIZUTANI and RAFTER (1969b) have shown that in the
bacterial reduction of sulfate, at any stage of reduction the remaining
sulfate is enriched not only in 34S, but also in 18 0. The ratio of the 34S
enrichment to the 18 0 enrichment has been found to be approximately
4:1.
c) Fractionations Due to Vapor Pressure Differences
Variations found in the isotopic composition of natural waters are
due to vapor pressure differences. The light isotopic component has a
higher vapor pressure than the heavy one, as has already been discussed.
IV. Sulfur
Sulfur has four stable isotopes with the following abundances (MACNAMARA and THODE, 1950):
32S:
95.02% ,
33S:
0.75% ,
34S:
4.21 % ,
36S:
0.02% .
Sulfur is present in nearly all natural environments: As a minor component in igneous and metamorphic rocks, mostly as sulfides; in the
biosphere and related organic substances, like crude oil and coal; in
ocean water as sulfate and in marine sediments as both sulfide and
sulfate. It may be a major component: In are deposits, where it is the
dominant nonmetal, and as sulfate in evaporites. This occurrence covers
the whole temperature range of geological interest. Sulfur is bound in
various valence states, from negatively charged sulfides, elemental sulfur,
B. Fractionation Mechanisms of Selected Elements
two-directional exchange method at temperatures above 350
0
C to obtain an alkali-feldspar-water calibration curve. O'NEIL and TAYLOR
(1966) also used the alkali ion exchange technique to obtain the muscovite-water calibration curve. These experiments were made by transforming kaolinite or paragonite to muscovite, and in both instances complete
oxygen isotope exchange accompanies the cation exchange.
The most suitable and sensitive mineral pair is the magnetite-quartz
pair. BERTENRATH et al. (1972) have redetermined the magnetite-water
curve, revising the curve given by O'NEIL and CLAYTON (1964).
Some of the experimentally determined calibration curves are shown
in Fig. 11.
b) Fractionations Due to Kinetic Processes
Oxygen isotope fractionations occurring during photosynthesis
(DOLE and JENKS, 1944) and respiration (LANE and DOLE, 1956) are
kinetic processes. MIZUTANI and RAFTER (1969b) have shown that in the
bacterial reduction of sulfate, at any stage of reduction the remaining
sulfate is enriched not only in 34S, but also in 18 0. The ratio of the 34S
enrichment to the 18 0 enrichment has been found to be approximately
4:1.
c) Fractionations Due to Vapor Pressure Differences
Variations found in the isotopic composition of natural waters are
due to vapor pressure differences. The light isotopic component has a
higher vapor pressure than the heavy one, as has already been discussed.
IV. Sulfur
Sulfur has four stable isotopes with the following abundances (MACNAMARA and THODE, 1950):
32S:
95.02% ,
33S:
0.75% ,
34S:
4.21 % ,
36S:
0.02% .
Sulfur is present in nearly all natural environments: As a minor component in igneous and metamorphic rocks, mostly as sulfides; in the
biosphere and related organic substances, like crude oil and coal; in
ocean water as sulfate and in marine sediments as both sulfide and
sulfate. It may be a major component: In are deposits, where it is the
dominant nonmetal, and as sulfate in evaporites. This occurrence covers
the whole temperature range of geological interest. Sulfur is bound in
various valence states, from negatively charged sulfides, elemental sulfur,