52
C. Variations of Stable Isotope Ratios in Nature
EpSTEIN and TAYLOR (1970), FRIEDMAN et al. (1970), and KAPLAN
and SMITH (1970) found unexpected high c5 13 C-values of about + 19%0 for
the lunar dust and between + 5 and + 11 %0 for the breccia. The finegrained rock showed a mean value of around - 24%0, which would agree
with the reduced carbon found in normal chondrites and with that found
in igneous rocks.
KAPLAN and SMITH (1970) and KAPLAN and PETROWSKI (1971) analyzed the sulfur isotopic composition in lunar samples. The finegrained
rock, contained the highest sulfur content, approximate average meteoritic sulfur whereas the bulk fines, lowest in S-concentration, were enriched in 34S by 5%0 and more.
II. Igneous Rocks
Magmas are the parent material of igneous rocks. They may originate through partial or complete fusion of pre-existing rocks. Besides a
silicate liquid, magmas usually contain suspended crystals, and sometimes a separate gas-phase. Because of its lower density than the surrounding rocks a magma tends to rise, and differentiation (the continuous evolution of magmas from a common parent) of the melt occurs in
response to the changing conditions. The most effective process of magmatic differentiation is fractional crystallization. In his classic model of
igneous petrogenesis, BOWEN (1928) assigned the key role to basaltic
magma. All other magmas were treated as products of fractional crystallization of the parent basaltic magma. Today, the importance of differentiation of basaltic magma by fractional crystallization to produce more
siliceous and alkaline magmas is generally accepted, however, differentiation of basalt can no longer be regarded as a universal mechanism of
magmatic evolution.
TAYLOR (1968a) has discussed the importance of 180rO measurements for igneous rock-types in relation to some of the classical problems of igneous petrology:
1) "the importance of fractional crystallization as a process of magmatic differentiation
2) whether assimilation of country rock plays an important role in magmatic
evolution
3) possible differences in mode of origin of volcanic and plutonic igneous rocks
4) the effects of late-stage deuteric or hydrothermal recrystallization in igneous
rocks, including the possible interaction between magmas and meteoric waters in
shallow portions ofthe earth's crust."
First the oxygen isotope composition of the various igneous rock
types is discussed in some detail (see Fig.21). Most of the data presented
in the following have been given by TAYLOR (1968 a).
C. Variations of Stable Isotope Ratios in Nature
EpSTEIN and TAYLOR (1970), FRIEDMAN et al. (1970), and KAPLAN
and SMITH (1970) found unexpected high c5 13 C-values of about + 19%0 for
the lunar dust and between + 5 and + 11 %0 for the breccia. The finegrained rock showed a mean value of around - 24%0, which would agree
with the reduced carbon found in normal chondrites and with that found
in igneous rocks.
KAPLAN and SMITH (1970) and KAPLAN and PETROWSKI (1971) analyzed the sulfur isotopic composition in lunar samples. The finegrained
rock, contained the highest sulfur content, approximate average meteoritic sulfur whereas the bulk fines, lowest in S-concentration, were enriched in 34S by 5%0 and more.
II. Igneous Rocks
Magmas are the parent material of igneous rocks. They may originate through partial or complete fusion of pre-existing rocks. Besides a
silicate liquid, magmas usually contain suspended crystals, and sometimes a separate gas-phase. Because of its lower density than the surrounding rocks a magma tends to rise, and differentiation (the continuous evolution of magmas from a common parent) of the melt occurs in
response to the changing conditions. The most effective process of magmatic differentiation is fractional crystallization. In his classic model of
igneous petrogenesis, BOWEN (1928) assigned the key role to basaltic
magma. All other magmas were treated as products of fractional crystallization of the parent basaltic magma. Today, the importance of differentiation of basaltic magma by fractional crystallization to produce more
siliceous and alkaline magmas is generally accepted, however, differentiation of basalt can no longer be regarded as a universal mechanism of
magmatic evolution.
TAYLOR (1968a) has discussed the importance of 180rO measurements for igneous rock-types in relation to some of the classical problems of igneous petrology:
1) "the importance of fractional crystallization as a process of magmatic differentiation
2) whether assimilation of country rock plays an important role in magmatic
evolution
3) possible differences in mode of origin of volcanic and plutonic igneous rocks
4) the effects of late-stage deuteric or hydrothermal recrystallization in igneous
rocks, including the possible interaction between magmas and meteoric waters in
shallow portions ofthe earth's crust."
First the oxygen isotope composition of the various igneous rock
types is discussed in some detail (see Fig.21). Most of the data presented
in the following have been given by TAYLOR (1968 a).