The oxygen isotope record in Murchison and other carbonaceous chondrites

The ranges of δ18O and δ17O in components of the Murchison (C2) chondrite exceed those in all other meteorites analyzed. Previous authors have proposed that C2 chondrites are the products of aqueous alteration of anhydrous silicates. A model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes. The minimum number (two) of initial isotopic reservoirs is assumed. Two major stages of reservoir interaction are required: one at high temperature to produce the16O-mixing line observed for the anhydrous minerals, and another at low temperature to produce the matrix minerals. The isotopic compositions severely constrain the conditions of the low-temperature process, requiring temperatures 44%. Extension of the model to the data on C1 chondrites requires aqueous alteration in a warmer, wetter environment.

[1]  T. E. Bunch,et al.  Carbonaceous chondrites. II - Carbonaceous chondrite phyllosilicates and light element geochemistry as indicators of parent body processes and surface conditions , 1980 .

[2]  H. Taylor,et al.  D/H and O18/O16 studies of serpentinization of ultramaflc rocks , 1974 .

[3]  R. Clayton,et al.  Mechanisms of hydrothermal crystallization of quartz at 250°C and 15 kbar , 1978 .

[4]  J. Kerridge.  MINERALOGY AND GENESIS OF THE CARBONACEOUS METEORITES. , 1968 .

[5]  R. Clayton,et al.  Oxygen isotopes in eucrites, shergottites, nakhlites, and chassignites , 1983 .

[6]  S. Epstein,et al.  The oxygen and hydrogen isotope geochemistry of clay minerals , 1970 .

[7]  R. Clayton,et al.  Oxygen isotope cosmothermometer , 1972 .

[8]  A. James,et al.  Oxygen isotope exchange between illite and water at 22°C , 1976 .

[9]  R. Clayton,et al.  Oxygen isotope fractionation in divalent metal carbonates , 1969 .

[10]  S. K. Runcorn,et al.  Mantles of the earth and terrestrial planets , 1967 .

[11]  R. Clayton,et al.  DISTRIBUTION OF THE PRE-SOLAR COMPONENT IN ALLENDE AND OTHER CARBONACEOUS CHONDRITES , 1977 .

[12]  Mitsuru Ebihara,et al.  Solar-system abundances of the elements , 1982 .

[13]  E. Anders,et al.  Chemical Evolution of the Carbonaceous Chondrites , 1962 .

[14]  R. Clayton,et al.  Correlated oxygen and magnesium isotope anomalies in Allende Inclusions, I: Oxygen , 1977 .

[15]  H. McSween.  Are carbonaceous chondrites primitive or processed? A review , 1979 .

[16]  Harry Y. McSween,et al.  Alteration in CM carbonaceous chondrites inferred from modal and chemical variations in matrix , 1979 .

[17]  E. Zen.  Problem of the thermodynamic status of the mixed-layer minerals , 1962 .

[18]  L. Fuchs,et al.  Mineralogy, mineral-chemistry, and composition of the Murchison (C2) meteorite , 1973 .

[19]  R. Clayton,et al.  The use of bromine pentafluoride in the extraction of oxygen from oxides and silicates for isotopic analysis , 1963 .

[20]  R. Clayton,et al.  Carbon Isotope Abundance in Meteoritic Carbonates , 1963, Science.

[21]  E. Anders,et al.  Isotopic anomalies of noble gases in meteorites and their origins. VI Presolar components in the Murchison C2 chondrite , 1980 .

[22]  J. McCrea.  On the Isotopic Chemistry of Carbonates and a Paleotemperature Scale , 1950 .

[23]  R. Clayton,et al.  A classification of meteorites based on oxygen isotopes , 1976 .