History of the paired lunar meteorites MAC88104 and MAC88105 derived from noble gas isotopes, radionuclides, and some chemical abundances

Conference · Fri Nov 01 04:00:00 EST 1991 · Geochimica et Cosmochimica Acta; (United States)

OSTI ID:5142649

Eugster, O; Burger, M; Kraehenbuehl, U; Michel, T ^[1]; Beer, J ^[2]; Finkel, R C ^[3]; Hofmann, H J; Synal, H A; Woelfli, W ^[4]

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1. Univ. of Bern (Switzerland)
2. Umweltphysik, Zuerich (Switzerland)
3. Paul Scherrer Inst. Zuerich (Switzerland)
4. Inst. fuer Mittelenergiephysik, Zuerich (Switzerland)

Noble gas isotopes, radionuclides, and chemical abundances were studied in the lunar meteorites MAC88104 and MAC88105 collected in the MacAlpine Hills area of Antarctica. The concentrations of the noble gas isotopes and the radionuclide activities in the two meteorites are essentially identical, proving that the two meteorites are paired. From {sup 40}K-{sup 40}Ar dating the authors obtain a gas retention age of 3,550 {plus minus} 400 Ma, typical for lunar surface material. Probably before breccia compaction the MAC88104/5 material resided for 630 {plus minus} 200 Ma at an average shielding depth of 85 g/cm{sup 2}, that is, about 50 cm below the lunar surface in the lunar regolith, as judged from the concentration of cosmic-ray produced Kr and Xe isotopes. Although this duration of lunar regolith residence is relatively long, MAC88104/5 represent immature regolith material: the concentration of solar wind implanted noble gases are two orders of magnitude lower than those in mature lunar soil. The {sup 40}Ar/{sup 36}Ar ratio of the trapped component is 5.7 {plus minus} 1.0, indicating an intermediate antiquity of the material; the authors estimate that the solar wind and lunar atmospheric particles were implanted about 2,000 Ma ago. The radionuclide activities allow a determination of the exposure history of the MAC88104/5 material. The duration of the Moon-Earth transfer was {much lt} 0.24 Ma. The exposure histories of the lunar meteorites discussed in this work indicate that at least two impact events are required for their ejection from the Moon. The authors first noble gas results for lunar meteorite Yamato-793274 show that it represents mature lunar regolith material with relatively high concentrations of solar wind implanted noble gas and a duration of several hundred million years of exposure to cosmic rays.

• OSTI ID: 5142649
• Report Number(s): CONF-9003166--
• Conference Information: Journal Name: Geochimica et Cosmochimica Acta; (United States) Journal Volume: 55:11
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ABUNDANCE
AGE ESTIMATION
ANTARCTIC REGIONS
ANTARCTICA
ARGON 36
ARGON 40
ARGON ISOTOPES
CHEMICAL COMPOSITION
ELEMENT ABUNDANCE
ELEMENTS
EVEN-EVEN NUCLEI
FLUIDS
GASES
GEOLOGIC HISTORY
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
LUNAR MATERIALS
MATERIALS
METEORITES
NONMETALS
NUCLEI
PETROGENESIS
POLAR REGIONS
QUANTITY RATIO
RARE GASES
STABLE ISOTOPES