Samarium-neodymium evolution of meteorites

Journal Article · Sat Feb 01 04:00:00 EST 1992 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(92)90099-5· OSTI ID:5226571

Prinzhofer, A; Papanastassiou, D A; Wasserburg, G J ^[1]

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1. California Inst. of Tech., Pasadena (United States)

The authors have obtained Sm-Nd data on two differentiated meteorites, Ibitira, a eucrite with distinct basaltic texture and with evidence of crystallization; and Morristown, a group 3A mesosiderite; as well as on Acapulco, an unclassified meteorite with chondritic chemical composition and a highly recrystallized texture. They have demonstrated the presence of in situ decay of short-lived {sup 146}Sm in these meteorites with initial abundance of {sup 146}Sm/{sup 144}Sm from 0.009 to 0.007 for the different meteorites. Precisely defined {sup 147}Sm-{sup 143}Nd internal isochrons were obtained yielding ages of 4.60 {+-} 0.03 AE for Acapulco, 4.47 {+-} 0.02 AE for Morristown, and 4.46 {+-} 0.02 AE for Ibitira. The corresponding initial {sup 143}Nd/{sup 144}Nd values obtained were 0.2 {+-} 0.9, 2.1 {+-} 0.7, and 1.6 {+-} 0.8 {var epsilon}u (epsilon units). Detailed consideration of the coupled {sup 147}Sm-{sup 143}Nd and {sup 146}Sm-{sup 142}Nd systematics and of the elevated initial {sup 143}Nd/{sup 144}Nd values indicates the presence of inconsistencies in the data for the two Sm-Nd parent-daughter pairs in spiteof the precise isochrons. The authors present a model which provides an interpretation of the paired Sm-Nd systematics in terms of an impulsive disturbance. The results indicate that three meteorites studied are relatively ancient objects, formed within the first 50 to 100 m.y. of the solar system, by planetary differentiation and impact processes, and were subjected to late metamorphism. The time of late metamorphism is substantially younger than 4.4 AE and possibly as recent as {approximately}3.9 AE. This metamorphism has resulted in partial, very limited reequilibration between plagioclase and phosphate, resulting in the observed shifts in initial {sup 143}Nd/{sup 144}Nd, Sm-Nd model ages, and the {sup 142}Nd/{sup 144}Nd abundances, but preserving the major temporal structures of early original formation and later disturbances.

• OSTI ID: 5226571
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 56:2; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
CHEMICAL COMPOSITION
CHEMISTRY
GEOCHEMISTRY
GEOLOGIC HISTORY
GEOLOGIC MODELS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
METAMORPHISM
METEORITES
MINERALOGY
MINERALS
NEODYMIUM ISOTOPES
OXYGEN COMPOUNDS
PHOSPHATE MINERALS
PYROXENES
RARE EARTH ISOTOPES
SAMARIUM ISOTOPES
SILICATES
SILICON COMPOUNDS