Geochemical Constraints on the Origin of the Moon and Preservation of Ancient Terrestrial Heterogeneities
S. J. Lock et al., Space Science Reviews, 216, 109, doi: 10.1007/s11214-020-00729-z, 2020 Geochemical constraints on the origin of the Moon and preservation of ancient terrestrial heterogeneities Simon J. Locka,∗, Katherine R. Berminghamb,c, Rita Paraid, Maud Boyete aDivision of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA. bDepartment of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854, USA cDepartment of Geology, University of Maryland,College Park, MD 20742, USA. dDepartment of Earth and Planetary Sciences, Washington University in St. Louis, Saint Louis, MO 63130, USA. eUniversit´eClermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000 Clermont-Ferrand, France. Abstract The Moon forming giant impact marks the end of the main stage of Earth's accretion and sets the stage for the subsequent evolution of our planet. The giant impact theory has been the accepted model of lunar origin for 40 years, but the parameters of the impact and the mechanisms that led to the formation of the Moon are still hotly debated. Here we review the principal geochemical observations that constrain the timing and parameters of the impact, the mechanisms of lunar formation, and the contemporaneous evolution of Earth. We discuss how chemical and isotopic studies on lunar, terrestrial and meteorite samples relate to physical models and how they can be used to differentiate between lunar origin models. In particular, we argue that the efficiency of mixing during the collision is a key test of giant impact models. A high degree of intra-impact mixing is required to explain the isotopic similarity between the Earth and Moon but, at the same time, the impact did not homogenize the whole terrestrial mantle, as isotopic signatures of pre-impact heterogeneity are preserved.
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