^1,2Yawooz A.Kettanah, ³Sabah A.Ismail
Journal of African Earth Sciences 139, 260-274 Link to Article [https://doi.org/10.1016/j.jafrearsci.2017.11.015]
¹Department of Applied Geosciences, College of Spatial Planning & Applied Sciences, Duhok University, Duhok, Iraq
²Department of Earth Sciences, Faculty of Graduate Studies, Dalhousie University, Halifax, NS, Canada
³Dean of the College of Education for Pure Sciences, Kirkuk University, Kirkuk, Iraq

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^1,2F. Thiessen, ^1,3A.A. Nemchin, ¹J.F. Snape, ¹J.J. Bellucci, ^1,2M.J. Whitehouse
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.03.023]
¹Department of Geosciences, Swedish Museum of Natural History, SE-10405 Stockholm, Sweden
²Department of Geological Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
³Department of Applied Geology, Curtin University, Perth, WA 6845, Australia
Copyright Elsevier

Apollo 12 breccia 12013 is composed of two portions, one grey in colour, the other black. The grey portion of the breccia consists mainly of felsite thought to have formed during a single crystallisation event, while the black part is characterized by presence of lithic fragments of noritic rocks and individual plagioclase crystals. In this study, U-Pb analyses of Ca-phosphate and zircon grains were conducted in both portions of the breccia. The zircon grains within the grey portion yielded a large range of ages (4154±7 to 4308±6 Ma, 2σ) and show decreasing U and Th concentrations within the younger grains. Moreover, some grains exhibit recrystallisation features and potentially formation of neoblasts. The latter process requires high temperatures above 1600-1700 ^oC leading to the decomposition of the primary zircon grain and subsequent formation of new zircon occurring as neoblasts. As a result of the high temperatures, the U-Pb system of the remaining original zircon grains was most likely open for Pb diffusion causing partial resetting and the observed range of ²⁰⁷Pb/²⁰⁶Pb ages. The event that led to the Pb loss in zircon could potentially be dated by the U-Pb system in Ca-phosphates, which have a weighted average ²⁰⁷Pb/²⁰⁶Pb age across both lithologies of 3924±3 Ma (95% conf.). This age is identical within error to the combined average ²⁰⁷Pb/²⁰⁶Pb age of 3926±2 Ma that was previously obtained from Ca-phosphates within Apollo 14 breccias, zircon grains in Apollo 12 impact melt breccias, and the lunar meteorite SaU 169. This age was interpreted to date the Imbrium impact. The zircon grains located within the black portion of the breccia yielded a similar range of ages (4123±13 to 4328±14 Ma, 2σ) to those in the grey portion. Given the brecciated nature of this part of the sample, the interpretation of these ages as representing igneous crystallisation or resetting by impact events remains ambiguous since there is no direct link to their source rocks via textural relationships or crystal chemistry. Similarly, the currently available zircon data set for all lunar samples may be distorted by partial Pb loss, resulting in meaningless and misleading age distribution patterns. Therefore, it is crucial to fully understand and recognize the processes and conditions that may lead to partial resetting of the U-Pb system in zircon in order to better constrain the magmatic and impact history of the Moon.

^1,2,3Nicola J. Potts, ^1,4Jessica J. Barnes, ^1,5Romain Tartèse, ¹Ian A. Franchi, ^1,6Mahesh Anand
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.03.022]
¹Planetary & Space Science, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
²Faculty of Earth & Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, NL
³School of GeoSciences, King’s Buildings, University of Edinburgh, Edinburgh, EH9 3JW, UK
⁴ARES NASA Johnson Space Center, Houston, TX 77058, USA
⁵School of Earth and Environmental Sciences, University of Manchester, Manchester M13 9PL, UK
⁶Department of Earth Sciences, The Natural History Museum, Cromwell Road, London, SW7 5BD UK
Copyright Elsevier

Compared to most other planetary materials in the Solar System, some lunar rocks display high δ³⁷Cl signatures. Loss of Cl in a H<<Cl environment has been invoked to explain the heavy signatures observed in lunar samples, either during volcanic eruptions onto the lunar surface or during large scale degassing of the lunar magma ocean. To explore the conditions under which Cl isotope fractionation occurred in lunar basaltic melts, five Apollo 14 crystalline samples were selected (14053,19, 14072,13, 14073,9, 14310,171 along with basaltic clast 14321,1482) for in situ analysis of Cl isotopes using secondary ion mass spectrometry. Cl isotopes were measured within the mineral apatite, with δ³⁷Cl values ranging from +14.6 ± 1.6 ‰ to +40.0 ± 2.9 ‰. These values expand the range previously reported for apatite in lunar rocks, and include some of the heaviest Cl isotope compositions measured in lunar samples to date. The data here do not display a trend between increasing rare earth elements contents and δ³⁷Cl values, reported in previous studies. Other processes that can explain the wide inter- and intra-sample variability of δ³⁷Cl values are explored. Magmatic degassing is suggested to have potentially played a role in fractionating Cl isotope in these samples. Degassing alone, however, could not create the wide variability in isotopic signatures. Our favored hypothesis, to explain small scale heterogeneity, is late-stage interaction with a volatile-rich gas phase, originating from devolatilization of lunar surface regolith rocks ∼4 billion years ago. This period coincides with vapor-induced metasomastism recorded in other lunar samples collected at the Apollo 16 and 17 landing sites, pointing to the possibility of widespread volatile-induced metasomatism on the lunar nearside at that time, potentially attributed to the Imbrium formation event.