Separation of spallation and terrestrial C-14 in chondrites

Details Separation of spallation and terrestrial C-14 in chondrites Separation of spallation and terrestrial C-14 in chondrites

Mar 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993lpi....24..341c&link_type=abstract

In Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F p 341-342 (SEE N94-12015 01-91)

Computer Science

Achondrites, Bruderheim Meteorite, Carbon 14, Carbonaceous Chondrites, Gas Analysis, Pyrolysis, Spallation, Carbon Dioxide, Contamination, Furnaces, Low Temperature, Oxygen

Scientific paper

Weathering products and contamination severely hamper our ability to accurately measure the C-14 spallation component in meteorites, but can give insights into a sample's terrestrial history. A procedure was developed to measure the C-14 in these components using CO and CO2 separations from temperature extractions from 200-500 mg of material. The Bruderheim (L6) chondrite was chosen as a standard following the practice of previous researchers, crosschecked against Peace River (L6), Abee (EH4), and Juvinas (EUC). Low temperature fractions (less than 900 C) give C-14 signatures consistent with a modern terrestrial C-14 source; melt fractions show elevated levels attesting to a spallogenic origin. Higher yields of CO in the melt fraction are less affected by the low levels of experimental contamination than the CO2. This fraction gave a mean CO:CO2 ratio in Bruderheim of 81.6 +/- 7.7; the ratio of the spallation component is 79.8 +/- 8.1. These values suggest equilibrium release of gases on the olivine-silica-pyroxene-iron buffer. This is corroborated by approximately equal release of the two components at 900 C. The chondrites gave an average saturation level of 54.3 +/- 2.9 dpm/kg; the achondrite gave 49.6 +/- 2.0 dpm/kg. No clear correlation with oxygen content is apparent, though shielding effects have yet to be evaluated. A further evaluation of this subject matter is given.

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