^1,2,3Hong Tang,^1,2,3XiongyaoLi,¹Xiaojia Zeng,^1,2,3Yang Li,^1,2,3Wen Yu,^1,2,3Bing Mo,^1,2,3Jianzhong Liu,⁴Shijie Wang,⁵Yongliao Zou
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114322]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
²CAS Center for Excellence in Comparative Planetology, China
³Key Laboratory of Space Manufacturing Technology, Chinese Academy of Sciences, Beijing 100094, China
⁴State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
⁵National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
Copyright Elsevier

The possibility of OH/H2O formation on the lunar surface has been proposed because of the interaction between protons from the solar wind and oxygen in the regolith. In this study, we examined olivine, pyroxene, plagioclase, and volcanic glass samples together irradiated with 7 keV H+ at a dose of 1017 ions/cm2 under the same experimental conditions to simulate the solar-wind proton implantation process on the moon. By comparing the infrared spectral characteristics of these samples before and after H+ implantation through an infrared spectrometer, we confirm that OH forms in all minerals and glass after H+ implantation, with a remarkable amount of OH/H2O found in plagioclase. This indicates that plagioclase can capture more H+ than other silicate phases to form the OH/H2O. The absorption characteristics of OH/H2O formed by H+ implantation are distinct and associated with the mineral structure. The efficiency of OH/H2O formation by H+ implantation is affected by crystal structure. We conclude that OH/H2O formed by solar-wind implantation in the lunar soil is likely to be mainly preserved in plagioclase, and the estimated OH/H2O absorption strength from 0.7 to 3.6% at 3356 cm−1 and from 0.9 to 4.8% at 3622 cm−1 of plagioclase is consistent with those found by recent lunar spacecraft missions

¹Thomas M.McCollom,^1,2Brian Hynek
Earth and Planetary Science Letters 557, 116729 Link to Article [https://doi.org/10.1016/j.epsl.2020.116729]
¹Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309, United States of America
²Department of Geological Sciences, University of Colorado, Boulder, CO 80309, United States of America
Copyright Elsevier

The hematite-bearing, sulfate-rich sandstones of the Burns formation at Meridiani Planum are underlain by a thin stratigraphic unit referred to as the Grasberg formation. The sulfate-bearing Grasberg rocks are fine-grained and lack bedding structures, and were previously interpreted to be a distinct lithologic unit based on morphological and chemical differences from the overlying Burns formation. However, reanalysis of the data indicates that, except for variable amounts of Mg, Ni, SO3 and Mn, the chemical compositions of the Grasberg and Burns rocks are very similar. The relatively low levels of Mg, Ni, and SO3 in the Grasberg rocks indicates that they have experienced diagenetic loss of Mg sulfates similar to that observed in a subset of eleven Burns formation rocks depleted in the same elements, including two Burns rocks immediately above the Grasberg contact. The Grasberg formation and Burns rocks near the contact have also evidently lost Mn during diagenesis. When compensated for diagenetic losses, rocks from the Grasberg and Burns formations are found to have nearly identical chemical compositions, albeit Grasberg rocks contained a few wt.% less SO3. These observations suggest that the sediment sources for the Grasberg and Burns formations are genetically related, and that both formations experienced some of the same diagenetic processes after deposition. Furthermore, the apparent loss of Mg, Ni, SO3, and Mn from the Grasberg formation and immediately overlying Burns rocks is mirrored by enrichments of these same elements in fractures within the underlying Shoemaker formation, suggesting downward movement of fluids during some diagenetic events.

¹Chris Yakymchuk,²Christopher L.Kirkland,³Aaron J.Cavosie,⁴Kristoffer Szilas,⁵Julie Hollis,⁶Nicholas J.Gardiner,⁴Pedro Waterton,⁷Agnete Steenfelt,⁸LaureMartin
Earth and Planetary Science Letters 557, 116730 Link to Article [https://doi.org/10.1016/j.epsl.2020.116730]
¹Department of Earth and Environmental Sciences, University of Waterloo, Canada
²Timescales of Mineral Systems Group, Centre for Exploration Targeting – Curtin Node, School of Earth and Planetary Sciences, Curtin University, Perth, Australia
³Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, Perth, Australia
⁴Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark
⁵Department of Geology, Ministry of Mineral Resources, Government of Greenland, P.O. Box 930, 3900 Nuuk, Greenland
⁶School of Earth and Environmental Sciences, University of St Andrews, St Andrews, KY16 9AL, United Kingdom
⁷The Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen K, Denmark
⁸Centre for Microscopy, Characterisation & Analysis, The University of Western Australia, Perth, Western Australia 6009, Australia
Copyright Elsevier

Large meteorite impacts have a profound effect on the Earth’s geosphere, atmosphere, hydrosphere and biosphere. It is widely accepted that the early Earth was subject to intense bombardment from 4.5 to 3.8 Ga, yet evidence for subsequent bolide impacts during the Archean Eon (4.0 to 2.5 Ga) is sparse. However, understanding the timing and magnitude of these early events is important, as they may have triggered significant change points to global geochemical cycles. The Maniitsoq region of southern West Greenland has been proposed to record a ∼3.0 Ga meteorite impact, which, if confirmed, would be the oldest and only known impact structure to have survived from the Archean. Such an ancient structure would provide the first insight into the style, setting, and possible environmental effects of impact bombardment continuing into the late Archean. Here, using field mapping, geochronology, isotope geochemistry, and electron backscatter diffraction mapping of 5,587 zircon grains from the Maniitsoq region (rock and fluvial sediment samples), we test the hypothesis that the Maniitsoq structure represents Earth’s earliest known impact structure. Our comprehensive survey shows that previously proposed impact-related geological features, ranging from microscopic structures at the mineral scale to macroscopic structures at the terrane scale, as well as the age and geochemistry of the rocks in the Maniitsoq region, can be explained through endogenic (non-impact) processes. Despite the higher impact flux, intact craters from the Archean Eon remain elusive on Earth.