Carbon Isotope Ratios during Metamorphism
107
ite-aragonite facies and a higher-temperature, epidote-rutile blueschist
facies.
HOEFS and EpSTEIN (1969) analyzed some migmatites, which seemed
to have "mixed values" between igneous and metamorphic rocks. These
values were interpreted as an indication of an out-of-equilibrium state.
WENNER and TAYLOR (1971) calculated temperatures of serpentinization of ultramafic rocks. They argued that many lizardite-chrysotile
serpentines must have formed at very low temperatures compared to the
antigorites. They suggested that the lizardite-chrysotile serpentinization
in most alpine ultramafic rocks may occur at temperatures significantly
lower than those given by most other investigators ('" 85 to 115
0
C).
Extending their investigation to bD-determinations, they showed that
meteoric groundwater is important in the serpentinization of many ultramafic rocks. Oceanic ultramafic samples show a uniform isotopic
composition, suggesting that seawater was involved in the serpentinization process.
3. DjH Ratios in Metamorphic Rocks
TAYLOR and EpSTEIN (1966b), and SHIEH and TAYLOR (1969a) have
studied hydrogen isotope variations during contact metamorphism. In
their investigation they have analyzed muscovite, biotite, and hornblende and found without exception that muscovite concentrates deuterium relative to coexisting biotite. Hornblende and biotite have almost
identical DjH ratios. When the hydrogen isotope data of minerals in
contact metamorphic rocks and their associated plutons are compared
with those from regional metamorphic rocks, it may be concluded that
in general, contact metamorphic rocks tend to have lower DjH ratios
than plutonic rocks (see Fig. 37). This implies that there was some type of
interaction of H20 (or H2) between the aureole and the intrusive.
In the contact metamorphic rocks and associated plutons there is a
rough correlation between DjH ratios and geographic locations of samples, which makes an isotope exchange with local meteoric groundwaters during contact metamorphism probable.
The DjH ratios of the pelitic rocks analyzed by SHIEH and TAYLOR
(1969a) do not show any obvious change across the contact metamorphic zones. The authors concluded that no significant fractionations
of hydrogen isotopes accompany contact metamorphic dehydration
reactions.
4. Carbon Isotope Ratios during Metamorphism
Marble is an abundant rock type in many regional metamorphic
terrains. The calcite-dolomite assemblage is stable over a wide range of
physical conditions. Carbon and oxygen isotope variations in meta-
107
ite-aragonite facies and a higher-temperature, epidote-rutile blueschist
facies.
HOEFS and EpSTEIN (1969) analyzed some migmatites, which seemed
to have "mixed values" between igneous and metamorphic rocks. These
values were interpreted as an indication of an out-of-equilibrium state.
WENNER and TAYLOR (1971) calculated temperatures of serpentinization of ultramafic rocks. They argued that many lizardite-chrysotile
serpentines must have formed at very low temperatures compared to the
antigorites. They suggested that the lizardite-chrysotile serpentinization
in most alpine ultramafic rocks may occur at temperatures significantly
lower than those given by most other investigators ('" 85 to 115
0
C).
Extending their investigation to bD-determinations, they showed that
meteoric groundwater is important in the serpentinization of many ultramafic rocks. Oceanic ultramafic samples show a uniform isotopic
composition, suggesting that seawater was involved in the serpentinization process.
3. DjH Ratios in Metamorphic Rocks
TAYLOR and EpSTEIN (1966b), and SHIEH and TAYLOR (1969a) have
studied hydrogen isotope variations during contact metamorphism. In
their investigation they have analyzed muscovite, biotite, and hornblende and found without exception that muscovite concentrates deuterium relative to coexisting biotite. Hornblende and biotite have almost
identical DjH ratios. When the hydrogen isotope data of minerals in
contact metamorphic rocks and their associated plutons are compared
with those from regional metamorphic rocks, it may be concluded that
in general, contact metamorphic rocks tend to have lower DjH ratios
than plutonic rocks (see Fig. 37). This implies that there was some type of
interaction of H20 (or H2) between the aureole and the intrusive.
In the contact metamorphic rocks and associated plutons there is a
rough correlation between DjH ratios and geographic locations of samples, which makes an isotope exchange with local meteoric groundwaters during contact metamorphism probable.
The DjH ratios of the pelitic rocks analyzed by SHIEH and TAYLOR
(1969a) do not show any obvious change across the contact metamorphic zones. The authors concluded that no significant fractionations
of hydrogen isotopes accompany contact metamorphic dehydration
reactions.
4. Carbon Isotope Ratios during Metamorphism
Marble is an abundant rock type in many regional metamorphic
terrains. The calcite-dolomite assemblage is stable over a wide range of
physical conditions. Carbon and oxygen isotope variations in meta-