Dusty Rocks in Gale Crater: Assessing Areal Coverage and Separating Dust and Rock Contributions in APXS Analyses

1Mariek E. Schmidt, 2,3Glynis M. Perrett, 1Samantha L. Bray, 1Nicholas J. Bradley, 1,4Rebekka E. Lee, 5Jeff A. Berger, 5John L. Campbell, 6Cathy Ly, 2Steven W. Squyres, 5Dustin Tesselaar
Journal of Geophysical Research, Planets Link to Article [https://doi.org/10.1029/2018JE005553]
1Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada
2Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, NY, USA
3Wilfrid Laurier University, Department of Physics and Computer Science, Waterloo, Ontario, Canada
4Lafarge Aggregates, Mississauga, Canada
5Department of Physics, University of Guelph, Guelph, Ontario, Canada
6Cornell University, Ithaca, NY, USA
Published by arrangement with John Wiley & Sons

A thin, patchy layer of airfall dust covers rock surfaces examined by the Mars Science Lab (MSL) rover Curiosity and complicates interpretation of textures in Mars Hand Lens Imager (MAHLI) images and compositions determined by Alpha Particle X‐ray Spectrometer (APXS). Using three image processing methods, we estimate dust coverages for MAHLI images of APXS targets to Sol 1512. Dust coverages of ‘as is’ rock targets range from 6 to 77% (±5 to 10% estimated error). Targets brushed by the Dust Removal Tool (DRT) range to lower coverages than ‘as is’ targets, but quality depends on surface type; brushed mudstones have the narrowest range and lowest coverages (11‐25%), while sandstones vary, ranging to higher coverages (12‐58%). Groups of rocks with similar compositions (APXS classes) can have strong correlations between dust coverage and SO3/Cl (up to r=0.985). Dust can also strongly affect the lightest elements measured (Na to Ca). By comparing paired ‘as is’ and DRT analyses, using the determined dust coverages, and finding a best fit dust thickness (generally ~10 μm), we model relative contributions of the dust and bedrock to extrapolate dust‐free compositions for homogeneous APXS classes. The dust is basaltic with high S and Cl. Dust‐free rocks have higher SiO2 and Na2O (up to 6.5 wt% and 0.5 wt% higher, respectively) and lower SO3 and CaO (up to 5.5 wt% and 1.3 wt% lower, respectively) than dusty equivalents. Dust most influences compositions that are very different from average Mars, including the alkali‐rich, MgO‐poor Jake M class.


Aqueous Processes from Diverse Hydrous Minerals in the Vicinity of Amazonian‐Aged Lyot Crater

1,2Lu Pan, 1,3Bethany L. Ehlmann
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2017JE005461]
1Division of Geological and Planetary Sciences, California Institute of TechnologyPasadena, CA, USA
2Laboratoire de Geologie de Lyon, Université Claude Bernard Lyon 1Villeurbanne, France
3Jet Propulsion Laboratory, California Institute of TechnologyPasadena, CA, USA
Published by Arrangement with John Wiley & Sons

Amazonian‐aged Lyot crater is the best‐preserved and deepest peak‐ring impact crater (diameter, D=220km) in the northern lowlands of Mars. Morphological features including scouring channels emanating from its ejecta and small channels within the crater have been examined previously to understand hydrological activity associated with the crater. In this study, we analyze images acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars Reconnaissance Orbiter (MRO) to investigate the mineralogical record in Lyot and its surroundings, which are presently enriched in ground ice, to understand the associated aqueous processes, their relative timing, and a possible role for ground ice in hydrous mineral formation. We find diverse hydrous minerals, including Fe/Mg phyllosilicates, chlorite, illite/muscovite and prehnite in Lyot crater walls, central peak, and ejecta, as well as in two craters to the west of Lyot. The exposure and distribution of the hydrous minerals suggests they are related to the impact process, either exposed by the excavation of hydrothermally altered rocks or formed through syn‐depositional hydrothermal alteration immediately after impacts. The Lyot impact induced channel formation to the north, but no mineralogical evidence of aqueous alteration associated with the channels is observed. The sinuous channels within Lyot, diverted by bedrock units with hydrous mineral detections, did not cause mineralization but likely represent the last stage of water activity in Lyot crater. The separate episodes of water activity indicate flow of liquid water on Mars’ surface during the Amazonian but limited to no aqueous alteration to generate hydrous minerals.

Formation of evolved rocks at Gale crater by crystal fractionation and implications for Mars crustal composition

1Arya Udry,2Esteban Gazel,3Harry Y. McSween Jr
Journal of Geophyisical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005602]
1Department of Geoscience, University of Nevada, Las Vegas
2Department of Earth and Atmospheric Sciences, Cornell University
3Department of Earth and Planetary Sciences, University of Tennessee
Published by Arrangement with John Wiley & Sons

The recent discovery of some ancient evolved rocks in Gale crater by the Curiosity rover has prompted the hypothesis that continental crust formed in early martian history. Here we present petrological modeling that attempts to explain this lithological diversity by magma fractionation. Using the thermodynamical software MELTS, we model fractional crystallization of different martian starting compositions that might generate felsic igneous compositions like those analyzed at Gale crater using different variables, such as pressure, oxygen fugacities, and water content. We show that similar chemical and mineralogical compositions observed in Gale crater felsic rocks can readily be obtained through different degrees of fractional crystallization of basaltic compositions measured on the martian surface. The results suggest that Gale crater rocks may not represent true primary liquids as they possibly accumulated and/or fractionated feldspar. In terms of major element compositions and mineralogy, we found that the Gale crater felsic compositions are more similar to fractionated magmas produced in Earth’s intraplate volcanoes than to terrestrial felsic continental crust as represented by tonalite‐trondhjemite‐granodiorite (TTG) suites. We conclude that the felsic rocks in Gale crater do not represent continental crust, as it is defined on Earth.

Spectral analysis of the Cerean geological unit crater central peak material as an indicator of subsurface mineral composition

1,2A.Galiano et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.05.020]
1IAPS-INAF, Via del Fosso del Cavaliere, 100, 00133 Rome, Italy
2 Università degli Studi di Roma Tor Vergata, Via della Ricerca Scientifica, 1, 00133 Rome, Italy
Copyright Elsevier

The dwarf planet Ceres is a heavily cratered rocky body, and complex craters with a central peak are widely observed on its surface. These types of craters form when a large body impacts the surface, generating extreme temperatures and pressures. During the impact event a large volume of rock is raised from the subsurface and a central uplift is formed. The material composing the central uplift is called crater central peak material (ccp) and the spectral analysis of such geologic areas can provide information about the composition of Ceres’ subsurface. Reflectance spectra of 32 ccps, acquired by the VIR spectrometer on board the NASA/Dawn spacecraft, were analysed and shows absorption bands located at about 2.7, 3.1, 3.4 and 4.0 µm which are also common on the Cerean surface. These absorptions are related, respectively, to Mg-phyllosilicates, NH4-phyllosilicates and Mg/Ca-carbonates.
The spectral parameters considered in this work are: spectral slopes estimated between 1.2 µm and 1.9 µm, band depths at 2.7-, 3.1-, 3.4- and 4.0-µm, and band centers near 4.0-µm. The ccps spectral parameters were analysed in conjunction with other Cerean parameters, such as the estimated depth of excavation of the material composing the central peak, in order to search for correlations and information about Ceres’ subsurface.
Central peak material located polewards show stronger 2.7- and 3.1-µm band depths with respect to those at the equatorial region, suggesting that subsurface deposits closer to poles are probably richer in Mg- and NH4-phyllosilicates. The 3.4-µm spectral feature is also deeper in ccps located at poleward latitudes, similar to the phyllosilicates. Conversely, the 4.0-µm band does not show this trend with latitude.
An increase in both 3.1- and 3.4-µm band depths with the estimated depth of excavation indicates that the spectral feature at 3.4-µm is the result of different contributions from carbonates and NH4-phyllosilicates, as expected. However, depending on their relative influence, the shape of the 3.4-µm spectral feature can vary.
Phyllosilicates and carbonates are the resulting products of aqueous alteration of chondritic material and, given the increasing abundance of such minerals (in particular ammoniated phyllosilicates) with depth of excavation, it is likely that our investigation involved subsurface layers nearby the boundary between the volatile-rich crust and the silicate-rich mantle.
Na-carbonate is found in the crater central peak material of Ernutet, Haulani and Ikapati, characterized by an estimated depth of excavation of about 6-9 km, where deposits of sodium carbonates could be locally present.

In situ organic compound analysis on a meteorite surface by desorption electrospray ionization coupled with an Orbitrap mass spectrometer

1,2Hiroshi Naraoka,2 Minako Hashiguchi
Rapid Communications in Mass Spectrometry 32, 959-964 Link to Article [https://doi.org/10.1002/rcm.8121]
1Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
2Research Center for Planetary Trace Organic Compounds, Kyushu University, Fukuoka, Japan

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Contrasting meteoritic signatures within the Clearwater East and Clearwater West impact structures: The view from osmium isotopes

1R. Terik Daly, 1Peter H. Schultz, 2John C. Lassiter, 2Staci W. Loewy, 3Lucy M. Thompson, 3John G. Spray
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.06.002]
1Department of Earth, Environmental and Planetary Sciences, Brown University, 324 Brook St, Box 1846, Providence, RI 02912, USA
2Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, 1 University Station C1100, Austin, TX 78712, USA
3Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada
Copyright Elsevier

Osmium isotopes provide a powerful tool for identifying meteoritic signatures in impactites. We apply the osmium isotope method to impact melt and country rocks from the Clearwater East and Clearwater West craters located in Quebec, Canada. Impact melts from Clearwater East have 187Os/188Os ratios of 0.1281 to 0.1285. These values indicate a significant meteoritic component, which exceeds that of all terrestrial craters studied to date, except Morokweng. Such findings align with earlier results from chromium isotopes and platinum-group elements. In contrast, impact melts from Clearwater West have 187Os/188Os ratios between 6.604 and 59.12. These highly radiogenic ratios are indistinguishable from the 187Os/188Os ratios in country rocks. Hence, osmium isotopes provide no evidence for a meteoritic component in impact melts at Clearwater West. The Clearwater craters formed in almost identical targets. Therefore, target effects cannot readily explain the stark difference between the two Clearwater craters. If melt sheet heterogeneity is similar at the two craters, the probability that melts at Clearwater West host an undetected chondritic component is < 0.1%. Multiple scenarios may explain the non-detection of a meteoritic signature at West; the possibility of a differentiated achondrite impactor could be tested using chromium isotopes. At Clearwater East, a low impact speed (<10 km s-1) may best explain the unusually strong meteoritic signature. Although the signature (or its nondetection) at each crater may be related to asymmetric preservation of the impactor component, the results presented here provide further evidence that Clearwater East and Clearwater West were temporally separate impact events.

Stand-off laser induced breakdown spectroscopy on meteorites: calibration-free approach

1M.Dell’Aglio, 2M.López-Claros, 2 J.J.Laserna,1,3,4S.Longo, 1,3A.De Giacomo
Spectrochimica Acta Part B: Atomic Spectroscopy 147, 87-92 Link to Article [https://doi.org/10.1016/j.sab.2018.05.024]
1CNR-NANOTEC, Via Amendola 122/D, 70126 Bari, Italy
2Universidad de Málaga, Facultad de Ciencias, Departamento de Química Analítica, Campus de Teatinos s/n, 29071 Málaga, Spain
3Chemistry Department, University of Bari, Via Orabona 4, 70126 Bari, Italy
4INAF Osservatorio Astrofisico di Arcetri, Largo E Fermi 5, 50125 Firenze, Italy

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