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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L15202, doi:10.1029/2006GL026446, 2006

Magnesium isotopic composition of olivine from the Earth, Mars, Moon, and pallasite parent body

M. D. Norman

Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia


G. M. Yaxley

Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia


V. C. Bennett

Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia


A. D. Brandon

NASA Johnson Space Center, Houston, Texas, USA


Abstract

To investigate the nebular history of material contributing to the terrestrial planets, and search for evidence of a high-temperature origin of the Moon, we measured Mg isotopic compositions of primitive olivines from the Earth, Moon, Mars, and pallasite parent body using laser-ablation multi-collector ICPMS. No temporal variation in the Earth's mantle since at least 3.8 Ga, and only limited variations in the compositions of mantle sources from diverse tectonic settings were found. Earth, Moon, Mars, and differentiated asteroids appear to have formed from a nebular reservoir that was homogeneous with respect to Mg isotopes. This implies either a minor role for evaporation-condensation in the inner solar system, or a limited variation in the proportion of refractory CAI-like material contributing to the terrestrial planets. The Mg isotopic composition of the Moon is identical to the Earth's mantle, placing strong constraints on any volatility-related fractionation that occurred during formation of the Moon.

Received 31 March 2006; accepted 11 July 2006; published 11 August 2006.

Index Terms: 1025 Geochemistry: Composition of the mantle; 1027 Geochemistry: Composition of the planets; 1041 Geochemistry: Stable isotope geochemistry (0454, 4870); 1060 Geochemistry: Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008).

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Citation: Norman, M. D., G. M. Yaxley, V. C. Bennett, and A. D. Brandon (2006), Magnesium isotopic composition of olivine from the Earth, Mars, Moon, and pallasite parent body, Geophys. Res. Lett., 33, L15202, doi:10.1029/2006GL026446.