¹Blanca Rincón-Tomás, ¹Bahar Khonsari, ¹Dominik Mühlen, ¹Christian Wickbold, ²Nadine Schäfer, ²Dorothea Hause-Reitner, ^1,3Michael Hoppert, ^2,3Joachim Reitner
International Journal of Astrobiology 15, 219-229 Link to Article [DOI: http://dx.doi.org/10.1017/S1473550416000264]
¹Georg-August-University Göttingen, Institute of Microbiology and Genetics, Grisebachstraße 8, 37077 Göttingen, Germany
²Georg-August-University Göttingen, Göttingen Centre of Geosciences, Goldschmidtstraße 3, 37077 Göttingen, Germany
³Göttingen Academy of Sciences and Humanities, Theaterstraße 7, 37073 Göttingen, Germany

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^1,2,3Nicola J. Potts,^1,4,5Romain Tartèse,^1,6Mahesh Anand,²Wim van Westrenen,^1,7Alexandra A. Griffiths,¹Thomas J. Barrett,¹Ian A. Franchi
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12681]
¹Planetary and Space Sciences, The Open University, Milton Keynes, UK
²Faculty of Earth and Life Sciences, VU University Amsterdam, 1081 HV Amsterdam, the Netherlands
³School of GeoSciences, University of Edinburgh, Edinburgh, UK
⁴Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, ⁵Muséum National d’Histoire Naturelle, Sorbonne Universités, CNRS, UPMC & IRD, Paris, France
⁶Department of Earth Sciences, The Natural History Museum, London, SW7 5BD, UK
⁷School of Earth, Atmospheric and Environmental Sciences, University of Manchester, UK
Published by arrangement with John Wiley & Sons

Recent studies geared toward understanding the volatile abundances of the lunar interior have focused on the volatile-bearing accessory mineral apatite. Translating measurements of volatile abundances in lunar apatite into the volatile inventory of the silicate melts from which they crystallized, and ultimately of the mantle source regions of lunar magmas, however, has proved more difficult than initially thought. In this contribution, we report a detailed characterization of mesostasis regions in four Apollo mare basalts (10044, 12064, 15058, and 70035) in order to ascertain the compositions of the melts from which apatite crystallized. The texture, modal mineralogy, and reconstructed bulk composition of these mesostasis regions vary greatly within and between samples. There is no clear relationship between bulk-rock basaltic composition and that of bulk-mesostasis regions, indicating that bulk-rock composition may have little influence on mesostasis compositions. The development of individual melt pockets, combined with the occurrence of silicate liquid immiscibility, exerts greater control on the composition and texture of mesostasis regions. In general, the reconstructed late-stage lunar melts have roughly andesitic to dacitic compositions with low alkali contents, displaying much higher SiO2 abundances than the bulk compositions of their host magmatic rocks. Relevant partition coefficients for apatite-melt volatile partitioning under lunar conditions should, therefore, be derived from experiments conducted using intermediate compositions instead of compositions representing mare basalts.

¹Paul A. Giesting,²Justin Filiberto
Meteoritics&Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12675]
¹Department of Earth and Planetary Science, University of Tennessee, Knoxville, Tennessee, USA
²Department of Geology, Southern Illinois University, Carbondale, Illinois, USA
Published by arrangement with John Wiley & Sons

Potassic-chloro-hastingsite has been found in melt inclusions in MIL 03346, its paired stones, and NWA 5790. It is some of the most chlorine-rich amphibole ever analyzed. In this article, we evaluate what crystal chemistry, terrestrial analogs, and experiments have shown about how chlorine-dominant amphibole (chloro-amphibole) forms and apply these insights to the nakhlites. Chloro-amphibole is rare, with about a dozen identified localities on Earth. It is always rich in potassium and iron and poor in titanium. In terrestrial settings, its presence has been interpreted to result from medium to high-grade alteration (>400 °C) of a protolith by an alkali and/or iron chloride-rich aqueous fluid. Ferrous chloride fluids exsolved from mafic magmas can cause such alteration, as can crustal fluids that have reacted with rock and lost H2O in preference to chloride, resulting in concentrated alkali chloride fluids. In the case of the nakhlites, an aqueous alkali-ferrous chloride fluid was exsolved from the parental melt as it crystallized. This aqueous chloride fluid itself likely unmixed into chloride-dominant and water-dominant fluids. Chloride-dominant fluid was trapped in some melt inclusions and reacted with the silicate contents of the inclusion to form potassic-chloro-hastingsite.