¹Harry Y.McSweenJr.,²Carol A.Raymond,³Edward M.Stolper,⁴David W.Mittlefehldt,³Michael B.Baker,⁵Nicole G.Lunning,⁶Andrew W.Beck,⁷Timothy M.Hahn
Geochemistry (Chemie der Erde) Link to Article [https://doi.org/10.1016/j.chemer.2019.07.008]
¹Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
⁴NASA Johnson Space Center, Houston, TX 77058, USA
⁵Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ 08854, USA
⁶Department of Petroleum Engineering and Geology, Marietta College, Marietta, OH 45750, USA
⁷Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA
Copyright Elsevier

Quantifying the amounts of various igneous lithologies in Vesta’s crust allows the estimation of petrologic ratios that describe the asteroid’s global differentiation and subsequent magmatic history. The eucrite:diogenite (Euc:Diog) ratio measures the relative proportions of mafic and ultramafic components. The intrusive:extrusive (I:E) ratio assesses the effectiveness of magma ascent and eruption. We estimate these ratios by counting numbers and masses of eucrites, cumulate eucrites, and diogenites in the world’s meteorite collections, and by calculating their proportions as components of crustal polymict breccias (howardites) using chemical mixing diagrams and petrologic mapping of multiple thin sections. The latter two methods yield a Euc:Diog ratio of ∼2:1, although meteorite numbers and masses give slightly higher ratios. Surface lithologic maps compiled from spectra of Dawn spacecraft instruments (VIR and GRaND) yield Euc:Diog ratios that bracket estimates of Euc:Diog from the meteorites. The I:E ratios from HEDs lie between 0.5–2.1:1, due to uncertainties in identifying cumulate eucrite. Gravity mapping of Vesta by the Dawn spacecraft supports the existence of diogenite plutons in the crust. Quantifying the proportion of high-density diogenitic crust in the gravity map yields I:E ratios of 0.8-1:2:1, values which are bracketed by calculations based on HEDs. The I:E ratio for Vesta is lower than for Earth and Mars, consistent with physical modeling of asteroid-size bodies. Nevertheless, it indicates a significant role for pluton emplacement during the formation of Vesta’s crust. These results are inconsistent with simple differentiation models that produce the crust by crystallization of a global magma ocean, unless residual melts are extracted into crustal magma chambers.

¹Emily J.Foote,¹David A.Paige,²Michael K.Shepard,³Jeffrey R.Johnson,⁴Stuart Biggar
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.113456]
¹University of California Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, CA 90095-1567
²Bloomsburg University, 400 E. Second St., Bloomsburg, PA 17815, Bloomsburg, PA
³Johns Hopkins University Applied Physics Laboratory, 11101 Johns Hopkins Road, 200-W230, Laurel, MD 20723-6005
⁴College of Optical Sciences, University of Arizona, 1630 E. University Blvd., P.O. Box 210094, Tucson, AZ 85721-0094
Copyright Elsevier

We have acquired a comprehensive laboratory bidirectional measurements of Apollo 11 and Apollo 16 lunar soil samples and have successfully fit photometric models to the laboratory data and have determined the solar spectrum averaged hemispheric reflectance as a function of incidence angle. The Apollo 11 (sample 10084) and 16 (sample 68810) soil samples are two representative end member samples from the Moon, dark lunar maria and bright lunar highlands. We used our solar spectrum averaged albedos in a thermal model and compared our model-calculated normal bolometric infrared emission curves with those measured by the LRO Diviner Lunar Radiometer Experiment. We found excellent agreement at the Apollo 11 site, but at the Apollo 16 site, we found that the albedos we measured in the laboratory were 33% brighter than those required to fit the Diviner infrared data. We attribute this difference at Apollo 16 to increased compaction and decreased maturity of the laboratory sample relative to the natural lunar surface, and to local variability in surface albedos at the Apollo 16 field area that are below the spatial resolution of Diviner.

¹Franck Poitrasson,¹Thomas Zambardi,²Tomas Magna,³Clive R.Neal
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.09.035]
¹Laboratoire Géosciences Environnement Toulouse, Centre National de la Recherche Scientifique UMR 5563 – UPS – IRD – CNES, 14-16, avenue Edouard Belin, 31400 Toulouse, France
²Czech Geological Survey, Klarov 3, CZ-11821 Prague 1, Czech Republic
³Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, USA
Copyright Elsevier

The Fe isotope composition of planetary bodies may provide constraints on their accretion modes and/or differentiation processes, but to do so, the Fe isotope systematics of key planetary reservoirs needs to be determined. To investigate this for the Moon, we measured the Fe isotope compositions for a suite of 33 bulk lunar mare basalts and highland rocks. Combined with published data, a compendium of 73 different lunar bulk rocks reveals a statistically significant Fe isotope difference between low-Ti and high-Ti mare basalts, yielding average δ⁵⁷Fe = 0.127 ± 0.012‰ (2SE; n = 27) and δ⁵⁷Fe = 0.274 ± 0.020‰ (2 SE; n = 25), respectively, relative to the IRMM-14 isotopic reference material. As lunar basalts are thought to reflect the Fe isotope composition of their respective mantle sources, the estimated relative proportion of the low-Ti and high-Ti source mantle suggests that the lunar upper mantle δ⁵⁷Fe value should be close to 0.142 ± 0.026‰. Whilst the composition of highland rocks (ferroan anorthosites and Mg-suite rocks) should provide a more global view of the Moon, the calculation of the mean δ⁵⁷Fe value of 15 available highland rock analyses yields δ⁵⁷Fe = 0.078 ± 0.124‰. Such a value is not defined precisely enough to be of critical use for comparative planetology. Ferroan anorthosites and Mg-suite rocks also give unresolvable means. It appears that Fe isotope heterogeneity among the lunar highland rocks is caused by non-representatively too small sample aliquots of coarse-grained rocks. It can also be the result of mixed lithologies for some. When the (kinetic) effect of olivine tending towards low δ⁵⁷Fe and feldspar with predominantly high δ⁵⁷Fe is cancelled, a more precise δ⁵⁷Fe value of 0.094 ± 0.035‰ is calculated. It is indistinguishable from the mean δ⁵⁷Fe of impact melts and is also similar to the upper lunar mantle estimate obtained from mare basalts. Collectively, this newly determined Fe isotope composition of the bulk Moon is indistinguishable from that of the Earth, and heavier than those reported for other planetary bodies. This planetary isotope relationship is only observed for silicon given the currently available mass-dependent stable isotope database. Because both iron and silicon reside in the Earth’s metallic core in significant quantities, this may point to the involvement of metallic cores of the Earth and Moon in the interplanetary Fe and Si isotope fractionation. Rather than via high-pressure metal–silicate fractionation at the core–mantle boundary, this would more likely be achieved by partial vaporization of the liquid outer metallic core in the aftermath of a Moon-forming giant impact.