| Title | Unraveling the evolution of chondrite parent asteroids by precise U-Pb dating and thermal modeling |
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| Author | Amelin, Y ; Ghosh,
A; Rotenberg, E |
| Source | Geochimica et Cosmochimica Acta vol. 69, no. 2, 2005 p. 505-518, https://doi.org/10.1016/j.gca.2004.05.047 |
| Links | Electronic Annex - Annexe numérique
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| Image |  |
| Year | 2005 |
| Alt Series | Earth Sciences Sector, Contribution Series 2005839 |
| Publisher | Elsevier BV |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Subjects | extraterrestrial geology; geochronology; geochemistry; radiometric dating; uranium lead dating; thermal analyses; thermal history; modelling |
| Illustrations | tables; Concordia diagrams; box plots; plots; models; photographs; photomicrographs |
| Program | NSERC Natural Sciences and Engineering Research Council of
Canada |
| Program | Canadian Space Agency, Funding Program |
| Released | 2005 01 01 |
| Abstract | U-Th-Pb isotopic data are reported for mineral fractions, individual chondrules and fractions of chondrule fragments from the equilibrated ordinary chondrite Richardton (H5). Chondrules and
milligram-sized fractions of pyroxene-rich chondrule fragments contain highly radiogenic Pb and concordant or nearly concordant U-Th-Pb isotopic systems, and are suitable for precise Pb-Pb age determinations. Olivine and sulfide have low U
concentrations and contain less radiogenic Pb. The ages of individual chondrules, pyroxene-rich and phosphate fractions are determined using U-Pb and Pb-Pb isochron and model date calculations. The Pb-Pb isochron date of 4562.7 ± 1.7 Ma of the
Richardton chondrules and chondrule fragments is resolved from the Pb-Pb isochron date of 4550.7 ± 2.6 Ma obtained from multiple phosphate fractions. Possible biases of the isochron dates due to single-stage approximation of multi-stage evolution,
contamination with modern common Pb, and disturbance to the system by reheating, are examined and are found to be insignificant. The chondrule and phosphate dates are interpreted as the timing of cessation of Pb diffusion during cooling following
metamorphism in chondrite parent bodies. The difference in estimated closure temperatures, ~950-1150 K for pyroxenes, and 700-800 K for phosphates (temperature estimates are based on published diffusion rates for Pb in pyroxenes and apatite), allows
evaluation of the average cooling rate at 26 ± 13 K/million years for the Richardton parent body over the period of 4563-4551 my. Thermal modeling of the H-chondrite parent body (which is assumed to be asteroid 6 Hebe, heated by decay of 26Al)
suggests a scenario in which accretion initiated at 1.7 m.y. after formation of calcium-aluminum-rich inclusions and continued for 3.5 m.y. |
| GEOSCAN ID | 222028 |
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