¹Thomas S. Kruijer,¹Lars E. Borg,¹William S. Cassata,¹Josh Wimpenny,¹Greg A. Brennecka,^2,3Charles K. Shearer,²Steven B. Simon
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.07.026]
¹Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Avenue (L-231), Livermore, CA 94550, USA
²Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, USA
³Lunar and Planetary Institute, Houston, TX
Copyright Elsevier

Alkali-suite rocks constitute one of three major suites of lunar crustal rocks. As such, constraining their formation timescales and petrogenesis is important for understanding the earliest magmatic history of the Moon. However, the magmatic history of alkali-suite rocks is partly obscured by superimposed effects of major basin-forming impact events on the lunar nearside. Consequently, unambiguous crystallization ages of samples from this suite of rocks have not been determined. The aim of this study is to better understand the petrogenetic history of the alkali-suite and the potential superimposed effects of impact metamorphism by determining Sm-Nd, Rb-Sr, and 40Ar/39Ar ages for an alkali anorthosite clast from Apollo 14 lithic breccia 14304 termed clast “b”. The new chronologic measurements of clast “b” yield concordant Sm-Nd, Rb-Sr, and 40Ar/39Ar ages of 3947±13 Ma, 3975±34 Ma, and 3937±37 Ma respectively, resulting in a weighted mean age of 3949±11 Ma. This age is not interpreted to date an igneous event related to production of the lunar highlands crust and instead the chronology and petrography of clast “b” are most readily explained by an impact event at ∼3.95 Ga that caused near-complete isotopic re-equilibration of the Sm-Nd, Rb-Sr, and 40Ar/39Ar chronometers. The weighted mean age of 3949±11 Ma of clast “b” is several hundred Ma younger than 4.3-4.4 Ga ages typically determined for samples of other crustal rock suites but in very good agreement with independent estimates for the formation of Imbrium basin ejecta and other marginally older impact events which are thought to have been sampled at the Apollo 14 landing site. Thus, although petrologic and geochemical examination suggest that clast “b” is a pristine igneous clast, its age likely records an impact event at the Apollo 14 landing site. Whereas the various determined ages of clast “b” do not reflect the timescales of alkali-suite magmatism, the relatively low initial Sr and Nd isotopic compositions of clast “b” indicate that its protolith evolved with very low 147Sm/144Nd and 87Rb/86Sr that are distinct from estimates for urKREEP but similar to that of lunar plagioclase. This implies that the igneous protolith of clast “b” derived from a plagioclase-dominated KREEP-rich source that must have formed after the formation of the urKREEP source at ∼4.35 Ga but well before the impact event recorded by clast “b” at ∼3.95 Ga.

¹Don R. Baker,^2,3Sara Callegaro,⁴Andrea Marzoli,⁵Angelo De Min,⁶Kalotina Geraki,⁷Martin J. Whitehouse,^2,3Agata M. Krzesinska,⁸Anna Maria Fioretti
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.08.007]
¹McGill University, Department of Earth and Planetary Sciences, Montréal, Quebec, Canada
²Centre for Earth Evolution and Dynamics (CEED), University of Oslo, Sem Sælands vei 2A N-0371 Oslo, Norway
³Centre for Planetary Habitability (PHAB), University of Oslo, Sem Sælands vei 2A, N-0371 Oslo, Norway
⁴University of Padova, Department of Land, Environment, Agriculture and Forestry, Legnaro, Italy
⁵Department of Mathematics and Geoscience, University of Trieste, via Weiss 2, 34128 Trieste, Italy
⁶Diamond Light Source, Harwell Science and Innovation Campus, Didcot, OX11 0DE, U.K
⁷Swedish Museum of Natural History, Stockholm, Sweden
⁸Instituto di Scienze Polari CNR, Padova Italy
Copyright Elsevier

The volatile concentrations of the martian mantle and martian magmas remain important questions due to their role in petrogenesis and planetary habitability. The sulfur and chlorine concentrations, and their spatial distribution, in clinopyroxenes from nakhlites MIL 03346, Nakhla, and NWA 998 were measured to provide insight into these volatiles in the parental melts and source regions of nakhlites, and to constrain the evolution of the nakhlite melts. Sulfur and chlorine in four clinopyroxene crystals from MIL 03346, four from Nakhla, and five from NWA 998 were measured in crystal cores and rims by synchrotron X-ray fluorescence using beamline I18 at the Diamond Light Source. Portions of two crystals from MIL 03346 and one from Nakhla were mapped for S and Cl; a few reconnaissance analyses of Cl and F in MIL 03346 and Nakhla were made by ion microprobe. Clinopyroxene cores in Nakhla and NWA 998 contain ∼ 10 ppm S, ∼ 10 ppm Cl and ∼ 74 ppm F (only Nakhla analyzed), whereas the cores of MIL 03346 contain ∼ 10 ppm S, ∼ 5 ppm Cl and ∼ 53 ppm F.

Using the volatile concentrations in the cores combined with previously determined partition coefficients we calculate that these clinopyroxenes crystallized from evolved basaltic melts containing ∼ 500 ppm S, ∼ 500 to 1900 ppm Cl, and 160 to 420 ppm F. These evolved melts can be used to calculate primitive melts in equilibrium with martian peridotite and the concentrations of S, Cl and F in the mantle source region of the nakhlite melts. Depending upon the extent of melting (5 to 30 %) necessary to produce the primary melts associated with nakhlites, our calculations indicate that the nakhlite source region has a S concentration between 20 (5 % melting) to 120 ppm (30 % melting), Cl between 16 to 97 ppm, and F between 14 to 48 ppm. These concentrations in the nakhlite magma source region are similar to previous estimates for the martian mantle; our calculated source region concentrations of F and Cl agree best with previous estimates if the martian mantle undergoes 10 to 20% melting to produce primary magmas that evolve to be parental to nakhlites. However, our maximum estimated sulfur concentration of the source (calculated for 30 % melting) is near previous minimum estimates for the martian mantle, suggesting the possibility that the nakhlite source region is depleted in sulfur relative to much of Mars’ mantle.

Mapping the spatial distribution of volatiles in three clinopyroxene crystals demonstrates that S and Cl concentrations of the evolving melts changed significantly from the core to the rim, particularly those in MIL 03346. Increasing S and Cl concentrations between the core and rim of MIL 03346 crystals are attributed to incorporation of additional volatiles through assimilation, but the Nakhla crystal shows no such evidence. However, concentrations of Cl and S at some outer crystal rims of one MIL 03346 crystal decrease, most probably due to volatile degassing during the final stages of clinopyroxene growth.

^1,2S.K. Bell,³D.J. Morgan,¹K.H. Joy,¹J.F. Pernet-Fisher,¹M.E. Hartley
Geochimica et Cosmochimica acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2023.08.009]
¹Department of Earth and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
²Rocktype Ltd, Magdalen centre, Oxford, UK
³School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
Copyright Elsevier

Mare basalts collected at the Apollo 15 landing site can be classified into two groups. Based on differing whole-rock major element chemistry, these groups are the quartz-normative basalt suite and the olivine-normative basalt suite. In this study we use modelling of Fe-Mg interdiffusion in zoned olivine crystals to investigate the magmatic environments in which the zonation was formed, be that within the lunar crust or during cooling within a surficial lava flow, helping to understand the thermal histories of the two basalt suites. Interdiffusion of Fe-Mg in olivine was modelled in 29 crystals in total, from six olivine-normative basalt thin sections and from three quartz-normative basalt thin sections. We used a dynamic diffusion model that includes terms for both crystal growth and intracrystalline diffusion during magma cooling. Calculated diffusion timescales range from 5 to 24 days for quartz-normative samples, and 6 to 91 days for olivine-normative samples. Similarities in diffusion timescales point to both suites experiencing similar thermal histories and eruptive processes. The diffusion timescales are short (between 5 and 91 days), and compositional zonation is dominated by crystal growth, which indicates that the diffusion most likely took place during cooling and solidification within lava flows at the lunar surface. We used a simple conductive cooling model to link our calculated diffusion timescales with possible lava flow thicknesses, and from this we estimate that Apollo 15 lava flows are a minimum of 3 to 6 m thick. This calculation is consistent with flow thickness estimates from photographs of lava flows exposed in the walls of Hadley Rille at the Apollo 15 landing site. Our study demonstrates that diffusion modelling is a valuable method of obtaining information about lunar magmatic environments recorded by individual crystals within mare basalt samples.

¹Zhongtian Zhang,¹David Bercovici
Proceedings of the National Academy of Sciences of the United States of America (PNAS) 120, 32 Link to Article [https://doi.org/10.1073/pnas.2221696120]
¹Department of Earth and Planetary Sciences, Yale University, New Haven, CT 06511

Paleomagnetic records of iron meteorites of the IVA group suggest that their parent body (an inward-solidified metal asteroid) possessed an internal magnetic field. The origin of this magnetism is enigmatic because inward solidification typically leads to light element release from the top of the liquid, which depresses convection and dynamo activity. Here, we propose a possible scenario to help resolve this paradox. The formation of a metal asteroid must involve a disruptive, mantle-stripping collision and the reaccretion of metal fragments. We hypothesize that a small portion of metal fragments may have substantially cooled before being reaccreted. These fragments could have formed a cold, rubble-pile inner core, which extracted heat from the liquid layer, leading to solidification and light element expulsion at the inner core boundary to power a dynamo. In the portions of the inward-growing crust that cooled below the remanence acquisition temperature, the magnetic field could be recorded.

¹Yunhua Wu,^2,3Weibiao Hsu,²Shiyong Liao,¹Zhiyong Xiao,⁴Xiaochao Che,⁵Lili Pan,²Ye Li,⁶Shaolin Li
Geochimica et Cosmochmica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.08.003]
¹Planetary Environmental and Astrobiological Research Laboratory, School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai 519082, China
²CAS Center for Excellence in Comparative Planetology, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China
³Deep Space Exploration Laboratory, University of Science and Technology, Hefei 230026, China
⁴Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 102206, China
⁵School of Earth Sciences and Engineering, Sun Yat-sen University, Zhuhai 519082, China
⁶Astronomical Research Center, Shanghai Science & Technology Museum, Shanghai 201306, China
Copyright Elsevier

Gabbroic and microgabbroic shergottites are intrusive igneous rocks on Mars and exhibit a wide variety of mineralogical and geochemical properties. However, their source reservoirs, magmatic processes and the link to other shergottite subtypes are not well constrained. Northwest Africa (NWA) 13581 is a newly found permafic olivine gabbro, representing a cumulate member in the shergottite group. This sample provides new critical constraints on the characteristics of mantle sources and magmatic evolution of shergottites. The texture and mineral chemistry of NWA 13581 indicate a polybaric crystallization condition, with an increase in oxygen fugacity of approximately 1 log unit after ascent and emplacement. Geochemical studies suggest that the sample is young (150 ± 25 Ma) and may share a similar enriched mantle reservoir (initial ε176Hfi = -18.4, initial ε143Ndi = -7.1) with shergottites like Zagami (basaltic shergottite), NWA 10169 (poikilitic shergottite) and Larkman Nunatak 06319 (olivine-phyric shergottite). In addition, the presence of potassium-rich melt inclusions enclosed in early-formed minerals of NWA 13581 implies a fertile source, probably originating from a metasomatized mantle. The occurrence of similar potassium-rich components in other enriched shergottites may suggest a common process in their mantle reservoir and during crystallization. Overall, NWA 13581 resembles poikilitic shergottites closer than typical gabbroic shergottites in several respects such as poikilitic texture, mineral chemistry, magmatic evolutionary path, and emplacement conditions. A simplified model is proposed for the formation of NWA 13581 and poikilitic shergottites in the same magma series. Magma mixing and/or assimilation are not the major mechanism that account for their slightly varied mineral modal abundances and quantitative textural characteristics. For samples derived from similar mantle sources, the textural and mineralogical diversities of shergottites are largely related to crystallization at different crustal levels.

^1,2Thomas J. Barrett,^1,2,3Katharine L. Robinson,^4,5Jessica J. Barnes,⁶G. Jeffrey Taylor,⁶Kazuhide Nagashima,⁶Gary R. Huss,³Ian A. Franchi,^3,7Mahesh Anand,^1,2David A. Kring 
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.08.004]
¹Center for Lunar Science and Exploration, Lunar and Planetary Institute, USRA, Houston, TX 77058
²NASA SSERVI
³School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
⁴ARES, NASA Johnson Space Center, Houston TX 77058, USA
⁵Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
⁶Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, Honolulu, HI 96822, USA
⁷Department of Earth Sciences, Natural History Museum, London SW7 5BD, UK
Copyright Elsevier

Apollo 15 quartz monzodiorites (QMDs) are reported to contain some of the most deuterium-depleted apatite found in lunar samples. In this study, apatite from six Apollo 15 QMDs, including three samples from 15405 not previously investigated, were analyzed for their H and Cl isotopes. Apatite in 15405 are extremely 2H (or D)-poor, with δD values ranging from – 658 ± 53 to − 378 ± 113 ‰, comparable to apatite data from related samples 15403 and 15404. In addition to new H isotope data, the first Cl-isotope data for lunar QMDs are presented. Apatite in 15405 and related samples are enriched in 37Cl with respect to Earth, with measured δ37Cl values ranging from + 13 to + 37 ‰. These values are within the reported δ37Cl range for KREEP-rich samples. The fact that the Cl isotopic composition of apatite in QMDs are similar to those in other lunar lithologies, but the H isotopic data are distinct and unique, provides possible further evidence for the existence of a D-poor reservoir in the lunar interior. Raman spectroscopy of the silica polymorph in sample 15405 reveals it to be a mixture of quartz and cristobalite. Based on available experimental data on the stability of various silica phases over a range of pressure and temperature regime, a deep-seated origin in the crust for QMDs may be possible which would support an endogenous origin of the H-Cl isotope systematics of the QMDs. The role of impact-induced transformation of silica phases and its contributing towards low D/H ratio in apatite, however, cannot be ruled out.

^1,2Morate D.,³Popescu M.,^1,2Licandro J.,^1,2Tinaut-Ruano F.,^1,2Tatsumi E.,^1,2de León J.
Monthly Notices of the Royal Astronnomical Society 519, 1677-1687 Link to Article [DOI 10.1093/mnras/stac3530]
¹Instituto de Astrofísica de Canarias (IAC), C/Vía Láctea s/n, Tenerife, La Laguna, E-38205, Spain
²Departamento de Astrofísica, Universidad de La Laguna, Tenerife, La Laguna, E-38205, Spain
³Astronomical Institute of the Romanian Academy, 5 Cut ¸itul de Argint, Bucharest, 040557, Romania
⁴Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan

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¹Oszkiewicz, Dagmara,¹Klimczak, Hanna,²Carry, Benoit,³Penttilä, Antti,⁴Popescu, Marcel,¹Krüger, Joachim,^5,6Aron Keniger, Marcelo
Monthly Notices of the Royal Astronomical Society 519, 2917-2928 Open Access Link to Article [DOI 10.1093/mnras/stac3442]
¹Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, Słoneczna 36, Poznań, P-60-286, Poland
²Observatoire de la Côte d’Azur, Cnrs, Universite Côte d’Azur, Laboratoire Lagrange, Nice, 06304, France
³Department of Physics, University of Helsinki, P.O. Box 64, Helsinki, FI-00014, Finland
⁴Astronomical Institute of the Romanian Academy, 5 Cutitul de Argint, Bucharest, 040557, Romania
⁵Nordic Optical Telescope, Rambla Jose Ana Fernández Perez 7, Breña Baja, E-38711, Spain
⁶Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, Aarhus C, DK-8000, Denmark

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^1,2,3Liu, Runchuan et al. (>10)
Science China Earth Sciences 66, 1399 – 1422 Link to Article [DOI 10.1007/s11430-022-1049-4]
¹State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
²Institutes of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China
³College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China

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¹Hoppe, Peter,²Rubin, Martin,³Altwegg, Kathrin
Space Science Reviews 219, 32 Open Access Link to Article [DOI 10.1007/s11214-023-00977-9]
¹Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, Mainz, 55128, Germany
²Physikalisches Institut, University of Bern, Sidlerstrasse 5, Bern, 3012, Switzerland
³Center for Space and Habitability, University of Bern, Sidlerstrasse 5, Bern, 3012, Switzerland

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