^1,2Tim E. Johnson, ¹Nicholas J. Gardiner, ¹Katarina Miljković, ¹Christopher J. Spencer, ¹Christopher L. Kirkland, ¹Phil A. Bland, ³Hugh Smithies
Nature Geoscience (in Press) Link to Article [https://doi.org/10.1038/s41561-018-0206-5]
¹School of Earth and Planetary Sciences, The Institute for Geoscience Research (TIGeR), Curtin University, Perth, Western Australia, Australia
²Center for Global Tectonics, State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, China
³Geoscience Directorate, Department of Mines, Industry Regulation and Safety, East Perth, Western Australia, Australia

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¹Nicholas J. Tosca,¹ Imad A. M. Ahmed, ²Benjamin M. Tutolo, ¹Alice Ashpitel, ³Joel A. Hurowitz
Nature Geoscience 11, 635-639 Link to Article [https://doi.org/10.1038/s41561-018-0203-8]
¹Department of Earth Sciences, University of Oxford, Oxford, UK
²Department of Geoscience, University of Calgary, Calgary, Alberta, Canada
³Department of Geosciences, Stony Brook University, Stony Brook, NY, USA

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¹Hardersen, P.S., ²Reddy, V., ³Cloutis, E., ⁴Nowinski, M., ⁵Dievendorf, M., ⁶Genet, R.M., ⁷Becker, S., ⁵Roberts, R.
Astronomical Journal 156, 11 Link to Article [DOI: 10.3847/1538-3881/aac3d2]
¹Planetary Science Institute, 1700 E. Fort Lowell Road, Tucson, AZ, United States
²Lunar and Planetary Laboratory, Department of Planetary Sciences, University of Arizona, 1629 E. University Boulevard, Tucson, AZ, United States
³Department of Geography, University of Winnipeg, Winnipeg, MB, Canada
⁴20406 Rosemallow Court, Sterling, VA, United States
⁵University of North Dakota, Department of Space Studies, Clifford Hall, 4149 University Avenue, Grand Forks, ND, United States
⁶4995 Santa Margarita Lake Road, Santa Margarita, CA, United States
⁷1218 Form Court, Odenton, MD, United States

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^1,2Steven J.Jaret, ^2,3Sidney R.Hemming, ¹E. Troy Rasbury, ⁴Lucy M.Thompson, ¹Timothy D.Glotch, ⁵Jahandar Ramezani, ⁴John G.Spray
Earth and Planetary Science Letters 501, 78-89 Link to Article [https://doi.org/10.1016/j.epsl.2018.08.016]
¹Department of Geosciences, Stony Brook University, Stony Brook, NY 11794, USA
²Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA
³Department of Earth and Environmental Sciences, Columbia University, New York, NY 10027, USA
⁴Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada
⁵Department of Earth Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Copyright Elsevier

As an analog for interpretations of the ages of martian shergottite meteorites, we have conducted an argon isotopic study of plagioclase feldspars exhibiting varying levels of shock from in and around the Manicouagan impact structure, Canada. Plagioclase from the impact melt sheet at Manicouagan yields an age of 215.40 ± 0.16 Ma, which indicates the time of impact. Plagioclase from a clast within melt-bearing breccias of the melt sheet and a hornfels adjacent to the melt sheet yield ages of 216 ± 3 Ma and 218 ± 7 Ma, respectively, which are interpreted to have been reset by contact metamorphism from the impact melt. Country rocks that were unaffected by the impact gives ∼849 Ma ages, consistent with the known Grenvillian target rock history. Maskelynite (amorphous plagioclase, which has been transformed in the solid state) yields an age of 567 ± 6 Ma. This age is geologically meaningless because it is not consistent with the target age, the impact age, or regional metamorphic ages at Manicouagan. Our results show that maskelynite argon ages are not meaningful, and that context is critical for proper interpretation of impact-affected argon ages.

¹Jeremy W.Boyce, ¹Sarah A.Kanee, ¹Francis M.McCubbin, ¹Jessica J.Barnes, ²Hayley Bricker, ³Allan H.Treiman
Earth and Planetary Science Letters 500, 205-214 Link to Article [https://doi.org/10.1016/j.epsl.2018.07.042]
¹NASA – Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, United States of America
²Department of Physics and Astronomy, UCLA, 475 Portola Plaza, Los Angeles, CA, 90095-1547, United States of America
³Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, United States of America
Copyright Elsevier

The relative abundances of chlorine isotopes measured in low-Ti basalts from the Moon appear to reflect mixing between two reservoirs: One component representing the urKREEP—the final product of the crystallization of the lunar magma ocean—with δ37Cl=+25‰(relative to Standard Mean Ocean Chlorine), the other representing either a mare basalt reservoir or meteoritic materials with
δ37Cl∼0‰. Using the abundances of other KREEP-enriched elements as proxies for the abundance of Cl in low-Ti mare basalts—which is difficult to constrain due to magmatic processes such as fractional crystallization and degassing—we find that the urKREEP contains ∼28 times higher Cl abundance (25–170 ppm Cl) as compared to the low-δ37 Cl end member in the observed mixing relationship. Chlorine—with an urKREEP/C.I. ratio of 0.2 to 1.5—is 500 to 3400 times less enriched than refractory incompatibles such as U and Th, and is consistent with incomplete loss of Cl species taking place during or prior to the magma ocean phase. The preservation of multiple, isotopically distinct reservoirs of Cl can be explained by: 1) Incomplete degassing pre- or syn-giant impact, with preservation of undegassed chondritic Cl and subsequent formation of an enriched and isotopically fractionated reservoir; or 2) Development of both high-concentration, high-δ37Cland low-concentration, low-δ37Cl reservoirs during the degassing and crystallization of the lunar magma ocean. A range of model bulk lunar Cl abundances from 0.3–0.6 ppm allows us to place Cl in the context of the rest of the elements of the periodic table, and suggests that Cl behaves as only a moderately volatile element during degassing. Chlorine isotope fractionation resulting from loss syn- or pre-magma ocean is characterized by 1000•ln⁡[α]=−3.96 to −4.04. Abundance and isotopic constraints are consistent with the loss of Cl being limited by vaporization of mixtures of Cl salts such as HCl, ZnCl2, FeCl2, and NaCl. These new constraints on the chlorine abundance and isotopic values of urKREEP make it a well-constrained target for dynamic models aiming to test plausible conditions for the formation of the Earth–Moon system.

¹Jean-Pierre Lorand, ^2,3R.H.Hewins, ⁴M.Humayun,²L.Remusat, ²B.Zanda, ¹C.La, ²S.Pont
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.08.041]
¹Laboratoire de Planétologie et Géodynamique à Nantes, CNRS UMR 6112, Université de Nantes, 2 Rue de la Houssinère, BP 92208, 44322 Nantes Cédex 3, France
²Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC) – Sorbonne Université- Muséum National d’Histoire Naturelle, UPMC Université Paris 06, UMR CNRS 7590, IRD UMR 206, 61 rue Buffon, 75005 Paris, France
³Department of Earth & Planetary Sciences, Rutgers University, Piscataway, NJ 08854, USA
⁴Department of Earth, Ocean & Atmospheric Science and National High Magnetic, Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
Copyright Elsevier

Unlike other martian meteorites studied so far, Martian regolith breccia NWA 7533 and paired meteorites that have sampled 4.4 Ga-old impact lithologies show only sulfides of hydrothermal origin (mostly pyrite (<1 vol.%) and scarce pyrrhotite). NWA 7533 pyrite has been analyzed for 25 chalcophile-siderophile trace elements with laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS). Micronuggets of highly siderophile elements-HSE (Os, Ir, Pt, Ru, Rh) along with occasional detection of Mo and Re were observed in half of the 52 analyzed crystals as random concentration spikes in time-resolved LA-ICPMS data. These nuggets are interpreted as variably altered remnants from repeated meteorite bombardment of the early martian crust, as are chondritic Ni/Co ratios of pyrite (10-20). Pyrite displays superchondritic S/Se (54,000 to 3,300) and Te/Se (0.3 – >1). The reasonably good positive correlation (R²=0.72) between Se and Ni reflects a temperature control on the solubility of both elements. Apart from the chalcogens S, Se and Te, pyrite appears to be a minor contributor (<20%) to the whole-rock budget for both HSE (including Ni and Co) and chalcophile metals Ag, As, Au, Cu, Hg, Pb, Sb, Tl and Zn. This deficit can result from i) high (>400°C) temperature crystallization for NWA 7533 pyrite, as deduced from its Se and Ni contents, ii) magmatic sulfide-depletion of brecciated early martian crust, iii) precipitation from near neutral H₂S-HS-H₂O-rich hydrothermal fluids that did not provide halogen ligands for extensive transport of chalcophile-siderophile metals. It is suggested that the 1.4 Ga lithification event that precipitated hydrothermal pyrite left the chalcophile-siderophile element budget of the early martian crust nearly unmodified, except for S, Se and Te.

¹Melinda J. Rucks, ^1,2Matthew L. Whitaker, ¹Timothy D. Glotch,^1,2 John B. Parise, ¹Steven J. Jaret, ¹Tristan Catalano, ³M. Darby Dyar
American Mineralogist 103, 1516-1519 Link to Article [https://doi.org/10.2138/am-2018-6539]
¹Department of Geosciences, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A.
²Mineral Physics Institute, Stony Brook University, Stony Brook, New York 11794-2100, U.S.A
³Department of Astronomy, Mount Holyoke College, South Hadley, Massachusetts 01075, U.S.A.
Copyright: The Mineralogical Society of America

Tissintite is a shock-induced, Ca-rich mineral, isostructural to jadeite, observed in several meteorite samples such as the martian shergottite Tissint. It may form within a “Goldilocks Zone,” indicating a potential to provide strict constraints on peak pressure and temperature conditions experienced during impact. Here we present the first laboratory synthesis of tissintite, which was synthesized using a large volume multi-anvil apparatus at conditions ranging from 6–8.5 GPa and 1000–1350 °C. For these experiments, we utilized a novel heating protocol in which we reached impact-relevant temperatures within 1 s and in doing so approximated the temperature-time conditions in a post-shock melt. We have established that heating for impact-relevant timescales is not sufficient to completely transform crystalline labradorite to tissintite at these pressures. Our findings suggest that tissintite forms from amorphous plagioclase during decompression.

^1,2Run-Lian Pang, ²Dennis Harries, ²Kilian Pollok, ¹Ai-Cheng Zhang, ^2,3Falko Langenhorst
American Mineralogist 103, 1502-1511 Link to Article [https://doi.org/10.2138/am-2018-6522]
¹State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China
²Institute of Geosciences, Friedrich Schiller University Jena, D-07745 Jena, Germany
³Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, U.S.A.
Copyright: The Mineralogical Society of America

Our investigations on the shocked eucrite Northwest Africa (NWA) 8003 revealed the occurrence of a new mineral, vestaite [IMA 2017-068;(Ti4+Fe2+)Ti3 4+O9]. This mineral coexists with corundum, ilmenite, and Al-Ti-rich pyroxene in shock melt pockets. It has an empirical chemical formula of
(Ti0.73 4+ Fe0.63 2+Al0.60Mn0.03Mg0.02Cr0.01)Ti3 4+O9
and the monoclinic C2/c structure of schreyerite. The ideal vestaite structure can be considered as a modular structure with an alternate intergrowth of M3O5-type (M = Ti4+,Fe2+,Al) and Ti2O4-type slabs. Alternatively, it can also be envisaged as a crystallographic shear structure with periodically shearing of rutile or α-PbO2 units. Streaking and splitting of diffraction spots observed in selected-area electron diffraction patterns indicate planar defects in the modular structure of vestaite. Our observations reveal that vestaite crystallized at high pressure (≤10 GPa) from a melt that represents a mixture of ilmenite and silicate components. A robust constraint on its formation conditions and stability field cannot yet be provided due to the lack of experimental data for these systems. Vestaite is a new, shock-generated mineral first found in a meteorite of the howarditeeucrite-diogenite (HED) clan, the largest achondrite group. Its discovery is not only of significance to the meteoritic mineralogy, but it could also be of interest to materials science.

¹Robbin Visser, ¹Timm John, ¹Martina Menneken, ²Markus Patzek, ²Addi Bischoff
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.08.037]
¹Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, 12249 Berlin
²Institut für Planetologie, WWU Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany
Copyright Elsevier

An important question regarding the formation of the solar system is how planetary bodies developed from dust and ice into the planets and planetary bodies. A particularly interesting topic is the thermal evolution of carbonaceous chondrites and volatile-rich clasts that could have originated from CM- and CI-like parent bodies. Two types of these volatile-rich clasts, which are a particular type of dark clasts, can be found. These clasts are mineralogically very similar to CM and CI chondrites and can occasionally be found in achrondritic meteorites. Mineral assemblages suggest that both CM and CI chondrites as well as volatile-rich clasts experienced low peak temperatures. However, these mineral assemblages only offer large estimated temperature ranges to describe the thermal history of CM and CI chondrites, and the thermal history of volatile-rich clasts has not been previously described. In this study, to gain a better understanding of the thermal history of both CM and CI chondrites and volatile-rich clasts, we estimated peak temperatures of 30 volatile-rich clasts (16 CI-, and 14 CM-like) in 10 different host meteorites (4 polymict ureilites, 5 polymict eucrites and 1 howardite) by Raman carbon thermometry. An automated method was developed in order to describe over 4000 collected Raman spectra using four pseudovoigt functions. The full width half maximum (FWHM) of the D1-band was then used to calculate peak temperatures. Results were then compared to Raman data of 8 different well-studied carbonaceous chondrites (including CI and CM chondrites) to evaluate the suggestion that volatile-rich clasts are composed of similar material to the equivalent CI and CM chondrites. Our results show that the peak temperatures experienced by CI-like clasts range between 30-110 °C with an average of about 65 ± 25 °C; the peak temperatures experienced by CM-like clasts range from 50-110 °C with an average of about 70 ± 25 °C. Six of the 8 studied carbonaceous chondrites (CM, CI, CR or C2ungr) also plot in the same low-temperature range between 50 °C and 75 °C and can thus be considered to have formed under similar temperature conditions as the volatile-rich clasts. This is in agreement with previous suggestions, based on their mineral compositions that volatile-rich clasts and CI and CM carbonaceous chondrites are composed of similar materials. The peak temperatures for carbonaceous chondrites determined in this study considerably reduce the range of temperature estimates proposed previously for these chondrites by different methods. By highlighting the ability of our methodology to evaluate data in an automated way, this study shows that Raman carbon thermometry is a good analytical technique for obtaining information about peak temperatures in small and delicate samples.

¹E.Quirico et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.08.029]
¹University Grenoble Alpes, CNRS, Institut de Planétologie et Astrophysique de Grenoble (IPAG), UMR 5274, Grenoble F-38041, France
Copyright Elsevier

Chondrites are exhumed from their parent bodies by impacts, which at the same time can result in heating and mechanical modification (compaction, deformation, fracturing, etc.). However, whether impacts are responsible for the occurrence of heated C2s remains controversial since radiogenic and solar heating have also been invoked to explain them. Here we report a Raman and infrared study of the composition and structure of Insoluble Organic Matter (IOM) in a series of 39 CM and C2-ungrouped chondrites. These parameters are tracers of the extent and nature of thermal metamorphism a meteorite has experienced and reflect the degree to which the thermally driven and irreversible carbonization of IOM has proceeded. We propose a carbon-based classification of heated C2 chondrites that reveals a high occurrence frequency of thermally processed C2 chondrites (> 36 %). This classification is in agreement with the mineralogical classification scheme of [Nakamura (2005) Post-hydration thermal metamorphism of carbonaceous chondrites. J. Mineral. Petrol. Sci. 100, 260–272]. Strongly heated C2 chondrites (PCA 02012, PCA 91008, Y 96720) display an IOM structural evolution that is dissimilar to that of type 3 chondrites that experienced long duration radiogenic thermal metamorphism. These differences almost certainly reflect kinetic constraints on IOM modification during short duration heating events. QUE 93005 is a weakly heated chondrite that experienced a retrograde aqueous alteration. Its very aliphatic-rich IOM points to a parent body hydrogenation through interactions with water. The closed-system conditions required by this mechanism could be satisfied by a kinetic confinement during a very short duration impact. MET 01072, a heavily compacted and uni-axially deformed chondrite, did not experience post-accretional heating. In this case, the deformation features probably reflect a low-velocity impact. In contrast, the weakly metamorphosed chondrite EET 96029 experienced one or several low pressure impacts that triggered mild heating and partial dehydration without deformation features. The study of a series of lithologies from the Tagish Lake C2-ungrouped chondrite confirms the coexistence of various degrees of post-accretional alteration, the most altered lithologies having experienced a moderate degree of heating. Overall, the high prevalence of heating in C2 chondrites, the evidence of short-duration heating in the most heated C2s and the ability of low velocity collisions to trigger heating favor impacts (against solar heating), as the dominant heating mechanism. Finally, our set of data does not support the action of a low temperature oxidation process that would control the aliphatic abundance in unheated primitive C2s.