Composition variations of major lunar elements: Possible impacts on lunar albedo spectra

1Fahad Zaman,1Lawrence W.Townsend,2Wouter Wet,1Harlan E.Spence,2Jody K.Wilson,2Nathan A.Schwadron,2Andrew P.Jordan,2Sonya S.Smith
Icarus (in Press) Link to Article []
1University of Tennessee, United States
2University of New Hampshire, United States
Copyright Elsevier

Understanding the elemental composition of the lunar regolith is important for expanding our knowledge of the history and geology of the Moon. Several methods have already been used to achieve this purpose, including direct analysis of lunar samples and satellite spectroscopy. Since computer modeling is important for processing the collected data, and for the preparation of future missions, this work uses Monte Carlo simulations to study the radiation emitted by the lunar surface, via nuclear interactions between the incident radiation environment and lunar regolith, to characterize the elemental composition of the Moon. When high energy primary galactic cosmic rays and solar energetic particles strike the lunar surface, they either scatter to free space or produce secondaries through cascades of interactions, some of which escape the lunar surface. Both the scattered primaries and escaping secondaries constitute the lunar “albedo” particles studied in this paper. The purpose of this work is to determine whether enhancing the abundances of any of the major lunar elements (O, Na, Mg, Al, Si, Ca, Ti, Mn, and Fe) causes an observable difference in the spectra of albedo particles emitted by the regolith. The model-based results herein show that charged albedo particles do not display any significant differences for any element. They also confirm that low-energy neutrons and gamma rays produce observable variations with different lunar compositions. This provides evidence that albedo neutrons and/or gamma rays, and not protons, are the source of the variations observed in a recent map of the lunar albedo, generated by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument.

53Mn-53Cr systematics of sphalerite in enstatite chondrites

1Jens Hopp,1,2Julian-Christopher Storck,1Thomas Ludwig,3Smail Mostefaoui,1Rainer Altherr,1,4,5Ulrich Ott,1Hans-Peter Meyer,1Mario Trieloff
Geochimica et Cosmochimica Acta (in Press) Link to Article []
1Institut für Geowissenschaften, Klaus-Tschira-Labor für Kosmochemie, Universität Heidelberg, Im Neuenheimer Feld 234-236, D-69120 Heidelberg, Germany
2Institut für Geologie, Universität Bern, Baltzerstrasse 1+3, CH-3012 Bern, Switzerland
3Institut de minéralogie, de physique des matériaux et de cosmochimie, Muséum National d’Histoire Naturelle, Case 52, 57 rue Cuvier, F-75231 Paris Cedex05, France
4MTA Atomki, Bem tér 18/c, HU-4026 Debrecen, Hungary
5Max-Planck-Institut für Chemie, Hahn-Meitner-Weg 1, D-55128 Mainz
Copyright Elsevier

We investigated the 53Mn-53Cr isotopic composition of a suite of enstatite chondrites by in situ analyses of various mineral phases with the Cameca IMS 1280-HR ion probe at Heidelberg, Germany, and a Cameca NanoSIMS at Paris, France. Only in sphalerite we found anomalies in 53Cr/52Cr-ratios correlating with 55Mn/52Cr which are due to decay of short-lived 53Mn (t1/2=3.7 Ma). A sphalerite in the EH-impact melt LAP 02225 showed the largest excess of 53Cr, with 53Cr/52Cr-ratios ranging up to 2.2. The calculated initial 53Mn/55Mn-ratios are within the range of previous Mn-Cr studies. We observed a spatial variation within a large sphalerite in LAP 02225, translating in distinct initial 53Mn/55Mn values. In case of the EL3 chondrite MAC 88136 the initial 53Mn/55Mn derived for one sphalerite is at the lower end of previously reported values and may reflect a variable influence of alteration-induced exchange of common Cr. This is supported by the total reset of the 53Cr/52Cr-ratio in another sphalerite in contact with an alteration vein irrespective of high Mn/Cr-ratios. Our observed initial 53Mn/55Mn-ratios of Sahara 97158, Indarch and EET 96135 correspond to the I-Xe systematics and hence, show that sphalerites can preserve reasonable age information. For Indarch however, if compared with other initial 53Mn/55Mn values from literature, a considerable scatter is obvious. This clearly demonstrates that the Mn-Cr system in sphalerite can be disturbed by various, still poorly investigated, processes (e.g., by thermal events, weathering, diffusion-controlled remobilization). Future application of Mn-Cr dating to sphalerite in enstatite chondrites thus requires a better understanding of how such processes influence the Mn-Cr systematics and demands for tools to identify the undoubtly present sphalerites carrying a true chronologic information.

The effect of carbon concentration on its core-mantle partitioning behavior in inner Solar System rocky bodies

1Damanveer S.Grewal,1Rajdeep Dasgupts,1Sanath Aithal
Earth and Planetary Science Letters 571, 117090 Link to Article []
1Department of Earth, Environmental, and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA
Copyright Elsevier

Partitioning of carbon (C) into the cores of rocky protoplanets and planets is one of the primary causes of its depletion in their bulk silicate reservoirs. Most of the experimental studies that determined the alloy to silicate meltpartition coefficient of carbon (DCalloy/silicate) have been conducted in graphite-saturated conditions. Because carbon is a minor element in all known protoplanetary and planetary cores, it is not known whether graphite-saturated DCalloy/silicate values are applicable to core-mantle differentiation in rocky bodies which likely occurred in C-poor conditions. In this study we experimentally determined DCalloy/silicate in MgO capsules with variable bulk C contents between oxygen fugacity (fO2) of IW–6.35 and IW–2.59 at a fixed P (3 GPa)-T (1700 °C). A mafic-ultramafic (NBO/T = 1.23-1.72) and mildly hydrous (bulk H = 44-161 ppm) nature of the silicate melts caused anhydrous C species (CO32− + CO) to dominate over a wider fO2 range (>IW–4.2) in comparison to previous studies. This resulted in an increase in DCalloy/silicate with decreasing fO2 from IW–2.6 to IW–4.2 followed by a drop at more reduced conditions due to the formation of C-H species. Importantly, DCalloy/silicate increases with increasing bulk C content of the system at a given fO2. Partitioning of C between alloy and silicate melts follows non-Henrian behavior (i.e., it depends on bulk C content) because the activity coefficient of C in the alloy melt (γCalloymelt) varies with C content in the alloy. Therefore, in addition to other intensive (PTfO2) and extensive variables (alloy and silicate melt compositions), DCalloy/silicate also depends on the bulk C content available during core-mantle differentiation. Consequently, previously determined DCalloy/silicate for C-rich alloys are not directly applicable for core-mantle differentiation in relatively C-poor magma oceans (MOs). Because the experiments from the present study more realistically simulate C-poor cores and mildly hydrous, mafic-ultramafic silicate MOs, our data can be used to more accurately predict C fractionation between MOs and cores in inner Solar System rocky bodies. Our study suggests that closed system MO-core equilibration should have led to less severe depletion of C in the silicate reservoirs of inner Solar System rocky bodies than previously predicted.

Exposure history, petrology, and shock-induced sulfidization reaction of Alatage Mountain 001 strewn field samples

1,2Shijie Li,3Ingo Leya,4Shijie Wang,3,4Thomas Smith,5,6Huiming Bao,1,7Yan Fan,1,2Bing Mo
Meteoritics & Planetary Science (in Press) Link to Article []
1Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081 China
2Chinese Academy of Sciences Center for Excellence in Comparative Planetology, Hefei, China
3Physikalisches Institut, Universität Bern, Bern, 3012 Switzerland
4State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
5Department of Geology and Geophysics, E235 Howe-Russell Geoscience Complex, Louisiana State University, Baton Rouge, Louisiana, 70803 USA
6Center for Isotope Effects Research and School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023 China
7Department of Geology, Northwest University, Xi’an, 710069 China
Published by arrangement with John Wiley & Sons

Several hundred meteorites with a total mass of over 100 kg were collected as the Alatage Mountain (AM) strewn field located in the Kumtag desert, Xinjiang Province, China. Twelve AM meteorites were studied in this work. Petrography, mineralogy, bulk chemistry, bulk oxygen isotopic compositions, and light noble gas concentrations and isotopic compositions were determined for all or for a selection of the meteorites. The studied meteorites are L-chondrites that suffered a very strong impact; impact melt veins and melt pockets are widely distributed. More than 50% of the troilite exists in the form of blebs and veins in olivine and pyroxene. Some of these meteorites are impact melt recrystallized rocks (e.g., AM 037). The strong impact caused the decomposition of troilite, which led in AM 034 to the sulfidization reaction of olivine. The metal in most meteorites is almost completely altered, and the troilite has been significantly oxidized. Weathering resulted in the depletion of Mg, Fe, Co, and Ni, and the enrichment of Sr, Ba, Pb, and U in these meteorites. The cosmic ray exposure (CRE) ages measured for these specimens range between 6.2 ± 1.9 Ma and 9.0 ± 2.7 Ma, depending on the cosmogenic nuclide used. The average CRE age is 7.6 ± 1.3 Ma. Both 4He and 40Ar gas retention ages indicate that the strong impact which caused the shock effects occurred about 320 Ma ago.

A Novel Atmospheric Removal Technique for TES Spectra Applied to Olivine and Carbonate-rich Bedrock in the Nili Fossae Region

1Steven W. Ruff,2Victoria E. Hamilton
Journal of Geophysical Research, Planets (in Press) Link to Articles []
1Arizona State University, School of Earth and Space Exploration
2Southwest Research Institute, Boulder, CO
Published by arrangement wíth John Wiley & Sons

Spectra from the Mars Global Surveyor Thermal Emission Spectrometer (TES) display a combination of features attributable to surface and atmospheric components. In order to fully recognize and interpret surface spectral features, the atmospheric spectral features must be removed through some form of surface-atmosphere separation (SAS). Multiple SAS techniques are available representing a range of complexity and accuracy. A ratio between spectra from a region of interest and a relatively spectrally bland, dusty location is an effective SAS technique, but the resulting ratio spectrum contains spectral features of surface dust from the dusty location. We exploit the uniform spectral character of surface dust across Mars to produce dust-removed ratio spectra (DRRS). This simple and robust technique allows TES spectra to be compared directly to laboratory spectra and to Mini-TES spectra from the Mars Exploration Rovers. Although previous SAS techniques yield atmospherically corrected spectra that can serve this purpose, they are more challenging to implement, retain fewer data points, and are less accurate in some cases. The DRRS technique provides an option that is well suited to both quick-look assessments of TES spectra and in-depth analyses using follow-on spectral modeling techniques. We show that DRRS of olivine -rich bedrock in the Nili Fossae region display spectral features that match olivine with a composition ranging from ∼Fo50 to

IIE irons: Origin, relationship to ordinary chondrites, and evidence for siderophile-element fractionations caused by chondrule formation

1Alan E.Rubin
Meteoritics & Planetary Science (in Press) Link to Article []
1Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, 90095–1567 USA
2Maine Mineral & Gem Museum, 99 Main Street, P.O. Box 500, Bethel, Maine, 04217 USAM
Meteoritics & Planetary Science (in Press) Link to Article []
Published by arrangement with John Wiley & Sons

IIE irons were derived from chondritic precursors that were the most reduced ordinary chondrites. The bulk chemical (e.g., Ir/Ni, Ir/Au, Au/Ni, Co/Ni) and bulk isotopic (i.e., Δ17O and δ74/70Ge) compositions of IIE irons lie along extensions of LL-L-H trends. Chondrule-bearing silicate clasts in IIE irons have mineralogical and petrological characteristics that extend LL-L-H trends; these clasts have higher modal metallic Fe-Ni and lower values for olivine Fa, low-Ca-pyroxene Fs, kamacite Co, and mean chondrule diameter. IIE irons are modeled as agglomerating before H-L-LL chondrites; they acquired more 26Al and reached the Fe,Ni-FeS eutectic temperature (˜940 °C). An FeS-rich metallic melt separated from unmelted silicate and drained to the core, eventually generating a dynamo. Most IIE metal remained within the crust/mantle region alongside recrystallized chondritic clasts. Alkali-rich IIE silicate inclusions formed from late-stage impacts via preferential melting of plagioclase. Some separation of K from Na occurred during vapor transport. Because most type I chondrules formed before most type II chondrules, the (type I)/(type II) modal ratio decreased from IIE to H to L to LL during agglomeration. Earlier-formed chondrules acquired higher abundances of refractory metal nuggets within CAI-fragment precursors, accounting for systematic changes in bulk OC of refractory/common siderophile and refractory/volatile siderophile ratios (IIE>H>L>LL). Because more Au and Co than Ni were retained in silicates, loss of metal globules from spinning partly molten type I chondrules caused systematic whole-rock decreases in Au/Ni and Co/Ni from IIE through LL. Expelled globules had different nebular aerodynamic properties than chondrules and drifted away (accounting, in part, for the metal/silicate fractionation).

The Ca isotope composition of mare basalts as a probe into the heterogeneous lunar mantle

1Martijn Klaver,1,2Tu-Han Luu,1Jamie Lewis,3Maximiliaan N.Jansen,4Mahesh Anand,5Johannes Schwieters,1Tim Elliott
Earth and Planetary Science Letters 570, 117079 Link to Article []
1Bristol Isotope Group, School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, United Kingdom
2Université de Paris, Institut de Physique du Globe de Paris. CNRS, F-75005 Paris, France
3School of Earth and Environmental Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3AT, United Kingdom
4School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
5Thermo-Fisher Scientific, Hannah-Kunath Strasse, Bremen, Germany
Copyright Elsevier

The Ca isotope compositions of mare basalts offer a novel insight into the heterogeneous nature of the lunar mantle. We present new high-precision Ca isotope data for a suite of low-Ti and high-Ti mare basalts obtained using our collision cell MC-ICP-MS/MS instrument, Proteus. Mare basalts were found to have a Ca isotope composition resembling terrestrial basalts (δ44/40CaSRM 915a =0.78–0.89‰) even though they are derived from a differentiated, refractory cumulate mantle source. Modelling of Ca isotope fractionation during crystallisation of a lunar magma ocean (LMO) indicates that the dominantly harzburgitic cumulates of the lunar interior should be isotopically heavier than Earth’s mantle (δ44/40CaSRM 915a =1.1–1.2‰ versus 0.93‰, respectively). These are balanced by an isotopically light lunar anorthosite crust, consistent with data for lunar anorthosite and feldspathic breccia meteorites.

We investigate the major element and Ca isotope composition of partial melts of various cumulate reservoirs by combining pMELTS models with equilibrium isotope fractionation mass balance calculations. The principal finding is that harzburgite cumulates alone are too refractory a source to produce low-Ti magmas. Partial melts of harzburgite cumulates have too low CaO contents, too high Al2O3/CaO and too high δ44/40CaSRM 915a to resemble low-Ti magmas. From Ca isotope constraints, we find that the addition of 10–15% of late-stage, clinopyroxenite cumulates crystallising at 95% LMO solidification is required to produce a suitable source that can generate low-Ti basalt compositions. Despite the addition of such late-stage cumulates pMELTS finds that these hybrid sources are undersaturated in clinopyroxene and are thus consistent with experimental constraints that the mantle sources of the lunar magmas are clinopyroxene-free. High-Ti basalts have slightly lower δ44/40CaSRM 915a (0.80–0.86‰) than low-Ti magmas (0.85–0.89‰) and clearly elevated TiO2/CaO. No suitable hybrid source involving ilmenite-bearing cumulates (IBC) was found that could reproduce melts with appropriate δ44/40Ca and major element systematics. Instead, we suggest that metasomatism of low-Ti mantle sources by IBC melts is the most plausible way to generate high-Ti magma sources and the rich diversity in TiO2 contents of lunar basalts and pyroclastic glasses.

Constraints on the origins of iron silicide spherules in ultrahigh-temperature distal impact ejecta

1Sergei Batovrin,1Boris Lipovsky,2Yury Gulbin,3Yury Pushkarev,3Yury A. Shukolyukov
Meteoritics & Planetary Science (in Press) Link to Article []
1Independent Researcher, 120 Casals Place, Bronx, New York, 10475 USA
2The Mining Institute of St. Petersburg, Vasilevsky ostrov, 21 Liniya, Dom 2, St. Petersburg, 199106 Russia
3Institute of Geology and Geochronology of Precambrian, RAS, Naberezhnaya Makarova 2, St. Petersburg, 199034 Russia
Published by arrangement with John Wiley & Sons

Terrestrially occurring iron silicide spherules, described in the geological literature for 160 years as cosmogenic and approved as “extraterrestrial” minerals by IMA CNMMN in 1984, so far have escaped any serious examination by meteoriticists. Our isotopic and REE data, obtained for silicide spherules for the first time, disagree with the meteoritic origin of gupeiite (Fe3Si) and xifengite (Fe5Si3) spherules from two continents. Despite departures from terrestrial norms (87Rb/86Sr—0.0174; 87Sr/86Sr—0.700181; 3He/4He—7.57 × 10−6; 40Ar/36Ar—325.9), the compositions of 143Nd/144Nd (0.512034) and 147Sm/144Nd (0.06357), as well as REE abundances, clarify provenance from upper crust sediments for samples with U/Pb age of 121–314 ka from the Ala-Tau range in the Urals. However, the morphology of flanged button shapes, ring waves, and eccentro-radiating ridges reliably constrains the origin of silicide spherules to distal meteoritic impact ejecta. Arc jet ablation experiments have previously demonstrated that similar morphologies, observed on australite tektites, reflect aerodynamic ablation rates corresponding to flight velocities well into orbital range. These features are generally accepted as conclusive evidence for hypervelocity atmospheric entry from space. Internal structure, consistent with accretion through the coalescence of 3–5 µm droplets, and composition, closely corresponding to 1893–1154 K span of C-type condensation sequences, indicate a high probability of processing through recondensation of ejecta vapor.

Organic matter in carbonaceous chondrite lithologies of Almahata Sitta: Incorporation of previously unsampled carbonaceous chondrite lithologies into ureilitic regolith

1Yoko Kebukawa et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article []
1Department of Chemistry and Life Science, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama, 240-8501 Japan
Published by arrangement with John Wiley & Sons

The Almahata Sitta (AhS) meteorite is a unique polymict ureilite. Recently, carbonaceous chondritic lithologies were identified in AhS. Organic matter (OM) is ubiquitously found in primitive carbonaceous chondrites. The molecular and isotopic characteristics of this OM reflect its origin and parent body processes, and are particularly sensitive to heating. The C1 lithologies AhS 671 and AhS 91A were investigated, focusing mainly on the OM. We found that the OM in these lithologies is unique and contains primitive isotopic signatures, but experienced slight heating possibly by short-term heating event(s). These characteristics support the idea that one or more carbonaceous chondritic bodies were incorporated into the ureilitic parent body. The uniqueness of the OM in the AhS samples implies that there were large variations in primitive carbonaceous chondritic materials in the solar system other than known primitive carbonaceous chondrite groups such as CI, CM, and CR chondrites.

Nano-FTIR spectroscopic identification of prebiotic carbonyl compounds in Dominion Range 08006 carbonaceous chondrite

1Mehmet Yesiltas,2Timothy D. Glotch,3Bogdan Sava
Scientific Reports 11, 11656 Link to Article [DOI]
1Faculty of Aeronautics and Space Sciences, Kirklareli University, Kirklareli, Turkey
2Department of Geosciences, Stony Brook University, Stony Brook, NY, USA
3Neaspec GmbH, 85540, Haar, Munich, Germany

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