Super-chondritic Sm/Nd in Mars, Earth, and the Moon
Abstract
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 (ɛ142Nd=-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).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.U13C..01C
- Keywords:
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- 1009 Geochemical modeling (3610;
- 8410);
- 1025 Composition of the mantle;
- 1027 Composition of the planets;
- 1040 Radiogenic isotope geochemistry;
- 1060 Planetary geochemistry (5405;
- 5410;
- 5704;
- 5709;
- 6005;
- 6008)