HR: 13:40h
AN: U13C-01    [Abstracts]
TI: Super-chondritic Sm/Nd in Mars, Earth, and the Moon
AU: * Caro, G
EM: caro@gps.caltech.edu
AF: Laboratoire Géochimie-Cosmochimie, Institut de Physique du Globe de Paris, 4, Place Jussieu, Paris, 75005, France
AU: Bourdon, B
AF: Institute of Isotope Geochemistry and Mineral Resources, ETH Zurich, Clausiusstrasse 25, Zurich, 8092, Switzerland
AU: Halliday, A N
AF: Department of Earth Sciences, University of Oxford, Parks Road, Oxford, OX1 3PR, United Kingdom
AU: Quitté, G
AF: Laboratoire des Sciences de la Terre, Ecole Normale Supérieure de Lyon, 46, allee d'Italie, Lyon, 69364, France
AB: Differences in the isotopic abundance of ¹⁴²Nd in planetary materials reflect the chronology and mechanisms by which crustal reservoirs formed during or shortly after accretion. Interpretation of these differences assumes that the terrestrial planets have a composition identical to that of chondritic meteorites. The ca. 20 ppm difference in ¹⁴²Nd/¹⁴⁴Nd between chondrites and the Earth's upper mantle may thus indicate very early (<30 Ma) formation and recycling of the first terrestrial crust [1]. However, it has also been suggested that the Earth may in fact be slightly non-chondritic in bulk composition. We present high-precision ¹⁴²Nd data for 16 martian meteorites showing that Mars also has a non-chondritic composition. Meteorites belonging to the Shergottite group define a planetary isochron yielding an age of differentiation of 40±18 Ma for the martian mantle. This isochron does not pass through the chondritic reference value (ε¹⁴²Nd=-21±3 ppm; ¹⁴⁷Sm/¹⁴⁴Nd=0.1966 [2]). The Earth, Moon and Mars appear to have all accreted in a portion of the inner solar system with 5% higher Sm/Nd when compared with material accreted in the asteroid belt. Such chemical heterogeneities in the accretion disk may have arisen from turbulent sorting of objects such as chondrules [3], which typically have high Sm/Nd (e.g. [4]). [1] Boyet, M. & Carlson, R. W., Science 214, 427-442 (2005). [2] Carlson, R. W., Boyet, M. & Horan, M., Science 316, 1175-1178 (2007). [3] Hewins, R. H. & Herzberg, C. T., Earth Planet. Sci. Lett. 144, 1-7 (1996). [4] Amelin, Y. & Rotenberg, E., Earth Planet. Sci. Lett. 223, 267-282 (2004).
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1025 Composition of the mantle
DE: 1027 Composition of the planets
DE: 1040 Radiogenic isotope geochemistry
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
SC: Union [U]
MN: 2007 Fall Meeting