CHROMIUM ISOTOPE SYSTEMATICS OF ACHONDRITES: CHRONOLOGY AND ISOTOPIC HETEROGENEITY OF THE INNER SOLAR SYSTEM BODIES
- The Pheasant Memorial Laboratory for Geochemistry and Cosmochemistry, Institute for Study of the Earth's Interior, Okayama University, 827 Yamada, Misasa, Tottori-ken, 682-0193 (Japan)
The standard planetary formation models assume that primitive materials, such as carbonaceous chondrites, are the precursor materials of evolved planetesimals. Past chronological studies have revealed that planetesimals of several hundred kilometers in size, such as the Howardite-Eucrite-Diogenite (HED) parent body (Vesta) and angrite parent body, began their differentiation as early as {approx}3 million years of the solar system formation, and continued for at least several million years. However, the timescale of planetesimal formation in distinct regions of the inner solar system, as well as the isotopic characteristics of the reservoirs from which they evolved, remains unclear. Here we present the first report for the precise {sup 53}Mn-{sup 53}Cr ages of monomict ureilites. Chemically separated phases from one monomict ureilite (NWA 766) yielded the Mn-Cr age of 4564.60 {+-} 0.67 Ma, identical within error to the oldest age preserved in other achondrites, such as angrites and eucrites. The {sup 54}Cr isotopic data for this and seven additional bulk ureilites show homogeneous {epsilon}{sup 54}Cr of {approx}-0.9, a value distinct from other achondrites and chondrites. Using the {epsilon}{sup 54}Cr signatures of Earth, Mars, and Vesta (HED), we noticed a linear decrease in the {epsilon}{sup 54}Cr value with the heliocentric distance in the inner region of the solar system. If this trend can be extrapolated into the outer asteroid belt, the {epsilon}{sup 54}Cr signatures of monomict ureilites will place the position of the ureilite parent body at {approx}2.8 AU. These observations imply that the differentiation of achondrite parent bodies began nearly simultaneously at {approx}4565 Ma in different regions of the inner solar system. The distinct {epsilon}{sup 54}Cr value between ureilite and carbonaceous chondrite also implies that a genetic link commonly proposed between the two is unlikely.
- OSTI ID:
- 21460145
- Journal Information:
- Astrophysical Journal, Vol. 720, Issue 1; Other Information: DOI: 10.1088/0004-637X/720/1/150; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ABUNDANCE
ACHONDRITES
ASTEROIDS
CHONDRITES
CHROMIUM 53
CHROMIUM 54
MANGANESE 53
MARS PLANET
METEOROIDS
NUCLEAR REACTIONS
NUCLEOSYNTHESIS
SOLAR SYSTEM
BETA DECAY RADIOISOTOPES
CHROMIUM ISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
INTERMEDIATE MASS NUCLEI
ISOTOPES
MANGANESE ISOTOPES
METEORITES
NUCLEI
ODD-EVEN NUCLEI
PLANETS
RADIOISOTOPES
STABLE ISOTOPES
STONE METEORITES
SYNTHESIS
YEARS LIVING RADIOISOTOPES