¹William Abbey et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.09.004]
¹Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109
Copyright Elsevier

The Mars Science Laboratory (MSL) rover, Curiosity, completed its first Martian year, 669 sols (687 Earth days), of operation on June 24, 2014. During that time the rover successfully drilled three full depth drill holes into the Martian surface and analyzed the recovered material using onboard instruments, giving us new insights into the potential habitability of ancient Mars. These drill targets are known as ‘John Klein’ (Sol 182) and ‘Cumberland’ (Sol 279), which lie in the mudstones of the Yellowknife Bay formation, and ‘Windjana’ (Sol 621), which lies in the sandstones of the Kimberley formation. In this paper we will discuss what was necessary to procure these samples, including: 1) an overview of the sampling hardware; 2) the steps taken to ensure sampling hardware is safe when drilling into a target (i.e., evaluation of rock type, rover stability, prior testbed experience, etc.); and 3) the drilling parameters used to acquire these samples. We will also describe each target individually and discuss why each sample was desired, the triage steps taken to ensure it could be safely acquired, and the telemetry obtained for each. Finally, we will present scientific highlights obtained from each site utilizing MSL’s onboard instrumentation (SAM & CheMin), results enabled by the drills ability to excavate sample at depth and transfer it to these instruments.

¹Pieter Vermeesch
Earth and Planetary Science Letters 501, 112-118 Link to Article [https://doi.org/10.1016/j.epsl.2018.08.019]
¹Department of Earth Sciences, University College London, United Kingdom
Copyright Elsevier

Point-counting data are a mainstay of petrography, micropalaeontology and palynology. Conventional statistical analysis of such data is fraught with problems. Commonly used statistics such as the arithmetic mean and standard deviation may produce nonsensical results when applied to point-counting data. This paper makes the case that point-counts represent a distinct class of data that requires different treatment. Point-counts are affected by a combination of (1) true compositional variability and (2) multinomial counting uncertainties. The relative magnitude of these two sources of dispersion can be assessed by a chi-square statistic and test. For datasets that pass the chi-square test for homogeneity, the ‘pooled’ composition is shown to represent the optimal estimate for the underlying population. It is obtained by simply adding together the counts of all samples and normalising the resulting values to unity. However, more often than not, point-counting datasets fail the chi-square test. The overdispersion of such datasets can be captured by a random effects model that combines a logistic normal population with the usual multinomial counting uncertainties. This gives rise to the concept of a ‘central’ composition as a more appropriate way to average overdispersed data. Two- or three-component datasets can be displayed on radial plots and ternary diagrams, respectively. Higher dimensional datasets may be visualised and interpreted by Correspondence Analysis (CA). This is a multivariate ordination technique that is similar in purpose to Principal Component Analysis (PCA). CA and PCA are both shown to be special cases of Multidimensional Scaling (MDS). Generalising this insight to multiple datasets allows point-counting data to be combined with other data types such as chemical compositions by means of 3-way MDS. All the techniques introduced in this paper have been implemented in the provenance R-package, which is available from http://provenance.london-geochron.com.

^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

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

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

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

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

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^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.