Evaluating urban micrometeorites as a research resource—A large population collected from a single rooftop

1M. D. Suttle,2T. Hasse,2,3L. Hecht
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13712]
1Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD UK
2Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstr. 43, Berlin, 10115 Germany
3Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstraße 74-100, Berlin, 12249 Germany
Published by Arrangement with John Wiley & Sons

We report the recovery and characterization of a new urban micrometeorite collection derived from the rooftop of an industrial building in Germany. We identified 315 micrometeorites (diameter: 55–515 µm, size peak: ˜150 µm, size distribution slope exponent: −2.62). They are predominantly S-type cosmic spherules (97.2%) but also two G-type spherules (0.6%), an unmelted coarse-grained single-mineral micrometeorite, and eight scoriaceous particles (2.5%) or particles transitional between scoriaceous micrometeorites and porphyritic spherules. Their analysis details how the magnetite rim on partially melted micrometeorites is progressively diluted as the melt fraction increases during heating. At least 10 micrometeorites contain platinum group nuggets (PGNs). They have chondritic compositions but are depleted in volatile Pd. However, a single nugget preserves chondritic Pd concentrations. We suggest that an Fe-Ni-S bead originally containing the PGN escaped its host cavity and wet the particle exterior, creating an Fe-rich melt that protected the nugget from evaporation. This melt layer oxidized forming magnetite—indicating that wetting events can affect the texture and composition of micrometeorites. Utilizing the well-constrained surface area (8400 m2) and rooftop age (21 yr), we attempted the first global mass flux estimate based on urban micrometeorite data. This produced anomalously low values (13.4 t yr–1), even when correcting for losses due to sample processing (<89.7 t yr–1). Our value is approximately two orders of magnitude lower than previous estimates, indicating that >99% of particles are missing, having been lost via drainage and cleaning. Rooftop collection sites have limited potential for mass flux calculations unless problems of loss can be resolved. However, urban micrometeorite collections have other advantages, notably exceptionally well-preserved particles with extremely young terrestrial ages and the ability to extract many micrometeorites from accessible sites. Urban micrometeorites should be considered complementary to Antarctic and deep-sea collections with potential for citizen science and educational exploitation.

Petrology and mineralogy of an igneous clast in the Northwest Africa 1685 (LL4) chondrite: Comparison with alkali-rich igneous clasts in LL-chondritic breccias

1,2Takafumi Niihara,3,4Tatsunori Yokoyama,5Tomoko Arai,3,6Keiji Misawa
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13719]
1Department of Systems Innovation, School of Engineering, University of Tokyo, Hongo 7-3-1, Tokyo, 113-8656 Japan
2University Museum, University of Tokyo, Hongo 7-3-1, Tokyo, 113-0033 Japan
3Department of Polar Science, The Graduate University for Advanced Studies (SOKENDAI), 10-3 Midoricho, Tachikawa, Tokyo, 190-8518 Japan
4Tono Geoscience Center, Japan Atomic Energy Agency, 959-31 Izumicho Jorinji, Toki, Gifu, 509-5102 Japan
5Planetary Exploration Research Center, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba, 275-0016 Japan
6National Institute of Polar Research, 10-3 Midoricho, Tachikawa, Tokyo, 190-8518 Japan
Published by arrangement with John Wiley & Sons

We have conducted petrological and mineralogical studies on an igneous clast in the Northwest Africa (NWA) 1685 (LL4) chondrite. This meteorite was described in the Meteoritical Bulletin as containing clasts similar to alkali-rich clasts in LL chondritic breccias Yamato (Y)-74442 (LL4), Bhola (LL3-6), and Krähenberg (LL5). We carefully compared the textures, as well as mineral and matrix compositions, of the NWA 1685 clast with those of the previously described alkali-rich clasts in the LL chondritic breccias. Olivine grains are embedded in glassy matrix and have no chemical zoning. Shock melt veins and fractures were observed only in olivine grains and did not continue into matrix. Potassium abundance of matrix glasses of the NWA 1685 clast is lower than those of alkali-rich igneous clasts in Y-74442, Bhola, and Krähenberg, indicating that the igneous clasts in NWA 1685 are different from the alkali-rich clasts previously reported in the LL chondritic breccias. The NWA 1685 clast might have formed during an impact melting and quenching event on the LL-chondrite parent body, and then been incorporated into a breccia.

Complicated pressure–temperature path recorded in the eucrite Padvarninkai

1Masaaki Miyahara,2,3Akira Yamaguchi,4Eiji Ohtani,5Naotaka Tomioka,6Yu Kodama
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13724]
1Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima, 739-8526 Japan
2National Institute of Polar Research, Tokyo, 190-8518 Japan
3Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, 190-8518 Japan
4Department of Earth Sciences, Graduate School of Science, Tohoku University, Sendai, 980-8578 Japan
5Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Nankoku, Kochi, 783-8502 Japan
6Marine Works Japan, Nankoku, Kochi, 783-8502 Japan
Published by arrangement with John Wiley & Sons

High-pressure minerals in the eucrite Padvarninkai were investigated. Parts of anorthitic plagioclase and tridymite in the host rock of Padvarninkai vitrified, indicating that the shock pressure was 22–27 GPa. Tissintite, coesite, and a majorite-bearing garnet occurred in the shock-melt veins of Padvarninkai as high-pressure minerals. Tissintite, kyanite, corundum, and dense plagioclase have occurred in the anorthitic plagioclase grains. The anorthitic plagioclase was melted and tissintite crystallized from the melt after the crystallization of kyanite and corundum. The residual melt became dense plagioclase by quenching. Tridymite has also melted and coesite crystallized from the melt. The formation of tissintite and coesite indicates that the shock pressure recorded in the veins was 2–13 GPa. The temperature increased drastically in the veins (>˜3000 K) compared with the host rock (<˜800 K). Parts of the tissintite and coesite became, respectively, amorphous (or anorthite) and quartz. Two different impact events may be recorded in Padvarninkai: The first impact event brecciated a part of the host rock, and the second impact event induced the melting of the brecciated portion, resulting in the formation of shock-melt veins where the conditions are a high temperature and a relatively low pressure. In the veins, tissintite and coesite formed first, and parts of them underwent a back-transformation due to a long cooling time.

Potassium elemental and isotope constraints on the formation of tektites and element loss during impacts

1Tomáš Magna,2,3Yun Jiang,4Roman Skála,2Kun Wang,5Paolo A.Sossi,4Karel Žák
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.07.022]
1Czech Geological Survey, Klárov 3, CZ-118 21 Prague 1, Czech Republic
2Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, MO 63130, USA
3CAS Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing CN-210033, China
4Institute of Geology of the Czech Academy of Sciences, Rozvojová 269, CZ-16500 Prague 6, Czech Republic
5Institut für Geochemie und Petrologie, ETH Zürich, Clausiusstrasse 25, CH-8092 Zürich, Switzerland
Copyright Elsevier

Potassium elemental and isotope systematics were investigated for a suite of central European tektites from three strewn sub-fields in Czech Republic and possible parent sedimentary materials from the vicinity of the Ries impact structure in SE Germany, supplemented by data for several other impact-related materials (bediasites, Ivory Coast tektites, Libyan Desert Glass). This is paralleled by computation of potential K loss and attendant isotope fractionation for physico–chemical conditions typical for formation of tektite precursor melts. These theoretical calculations indicate a <0.1% loss of K from tektite precursor melts up to 2,500K and <0.002‰ change in the 41K/39K ratio even for a small sphere of 0.002 m at 2,500K, precluding any significant K loss and isotope fractionation. Numerical modelling also indicates that differential velocities between surrounding gas and liquid are not sufficient to remove the gaseous boundary layer, such that the partial pressure of potassium developed around the molten moldavite beads impedes further evaporation and also contributes to back-condensation of the already evaporated potassium.

Central European tektites (moldavites) are enriched in K compared to the assumed sedimentary sources from the wider Ries area whereby the latter materials do not exceed 2.9 wt.% K2O compared to 2.5–4.1 wt.% K2O in moldavites. The apparent K enrichment in moldavites may be explained by a yet unaccounted process during formation of tektite precursor melts and/or unidentified source, such as volcanoclastic deposits that were produced by large Mid-Miocene volcanic centers in the Pannonian Basin. The K isotope compositions of tektites are more variable than those of sediments from the wider Ries area but they largely overlap (δ41K from −0.78 ± 0.03‰ to −0.13 ± 0.03‰ versus −0.72 ± 0.03‰ to −0.28 ± 0.02‰, respectively). These ranges mimic 41K/39K variations reported for igneous and sedimentary portions of the upper continental crust (δ41K roughly between −0.7 and −0.1‰). They show a slight difference among the three investigated strewn sub-fields, depending on their respective distance from the impact. In detail, moldavites from the closest strewn sub-field in the Cheb Basin show predominantly heavy K isotope compositions and those from the farthest strewn sub-field in Western Moravia are uniformly isotopically light. The origin of this difference may reflect lithological heterogeneity of the target area.

Potassium contents in bediasites and Ivory Coast tektites range between 1.3 and 1.8 wt.% K2O and their corresponding δ41K values vary from −0.57 ± 0.02‰ to −0.41 ± 0.03‰. Both ranges are significantly narrower than those observed for moldavites. When compared to data for possible sedimentary precursors in the Chesapeake Bay and Bosumtwi impact structure, respectively, it is apparent that these tektites were neither depleted nor enriched in potassium. The extent of their K isotope fractionation relative to plausible sources remains unconstrained. The Libyan Desert Glass displays invariant δ41K of ∼ −0.57 ± 0.06‰ at ≤0.01 wt.% K2O. Given the silica-rich nature of LDG and the lack of possible parent materials, no further constraints can be placed at present to further resolve the source material or reveal details of LDG formation process.

Identification and pairing reassessment of unequilibrated ordinary chondrites from four Antarctic dense collection areas

1Kevin Righter,2John Schutt,1Nicole Lunning,2Ralph Harvey,3James Karner
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13707]
1ARES, Mailcode XI2, NASA-JSC, Houston, Texas, 77058 USA
2Department of Earth, Environmental, and Planetary Science, Case Western Reserve University, 10900 Euclid Ave, Cleveland, Ohio, 44106 USA
3Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, 84113 USA
Published by arrangement with John Wiley & Sons

New analyses of Cr2O3 contents of olivines from type II chondrules in unequilibrated chondrites (UOC) from four dense collections are reported here. This survey of petrologic type 3 UOCs was undertaken to identify primitive chondrites that may have been overlooked, and to address possible pairing errors. We have identified 23 primitive UOCs (≤3.10) (only five identified previously, for a total of 28 overall), and also recommend other revisions to prior classifications and pairings.

Nickel–manganese variability in olivine and Al-in-olivine thermometry for olivine-phyric shergottites

1Sierra R. Ramsey,1,2Geoffrey H. Howarth,3Arya Udry,4,5,6Juliane Gross
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13721]
1Department of Geology, University of Georgia, 210 Field Street, Athens, Georgia, 30602 USA
2Department of Geological Sciences, University of Cape Town, Rondebosch, 7701 South Africa
3Department of Geoscience, University of Nevada, Las Vegas, 4505 S. Maryland Pkwy, Las Vegas, Nevada, 89154 USA
4Department of Earth and Planetary Sciences, Rutgers University, 610 Taylor Rd, Piscataway, New Jersey, 08854 USA
5Department of Earth and Planetary Sciences, The American Museum of Natural History, 200 Central Park West, New York, New York, 10024 USA
6Lunar and Planetary Institute, 3600 Bay Area Blvd, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

Olivine-phyric shergottites represent primitive Martian magmas, but they commonly contain excess olivine and rarely represent primary mantle melts. Olivine chemistry, however, tracks magma evolution and preserves information on the original parent magma composition. Here, we investigate the applicability of the Al-in-olivine thermometer in tandem with olivine chemistry in a suite of 13 olivine-phyric shergottites to constrain the compositions and conditions of their mantle sources and parental magmas. We show that the Al-in-olivine thermometer is a robust method for constraining crystallization temperatures in shergottites, yielding temperatures in agreement with experimental work. In contrast, we do not recommend olivine–spinel thermometry relying on Mg-Fe in olivine, which underestimates crystallization temperatures by 160–380 °C. Olivine chemistry reveals distinct differences in Ni concentrations between shergottite groups, with enriched shergottites generally having higher Ni at a given forsterite (Fo) content. Nickel variations in terrestrial olivine are often accredited to contributions from a pyroxenite source; however, the same mechanism is not responsible for Ni variations in Martian olivine. Here, we favor a model for variable olivine modal abundance, caused by multiple melting episodes in the depleted mantle source, affecting Ni partitioning during melting to account for the Ni variations observed. In addition, we show that olivine Ni-Mn variations in depleted shergottites indicate variable petrogenetic histories and parental magmas. Tissint contains elevated Ni in olivine more similar to the enriched shergottites whereas DaG 1037 has elevated Mn in olivine suggesting an Mn-enriched parent magma relative to other depleted shergottites.

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 [https://doi.org/10.1111/maps.13710]
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 Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081 China
5Department of Geology and Geophysics, E235 Howe-Russell Geoscience Complex, Louisiana State University, Baton Rouge, Louisiana, 70803 USA
6International Center 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.

Trace Elemental Behavior in the Solar Nebula: Synchrotron X-ray Fluorescence Analyses of CM and CR Chondritic Iron Sulfides and Associated Metal

Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.07.016]
1Department of Earth and Planetary Sciences, MSC-03 2040 1 University of New Mexico, Albuquerque, NM 87131, USA
2Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA
3Center for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637, USA
Copyright Elsevier

We have performed a coordinated focused ion beam (FIB)-scanning and transmission electron microscopy (SEM, TEM), electron probe microanalysis (EMPA)-synchrotron X-ray fluorescence (SXRF) microprobe study to determine phase-specific microstructural characteristics and high-resolution in situ trace element concentrations of primary pyrrhotite, pentlandite, and associated metal grains from chondrules in CM2 and CR2 carbonaceous chondrites. This work is the first of its kind to link trace element chemical and microstructural observations in chondritic sulfides in an attempt to determine formation mechanisms and conditions of primary sulfides in these meteorite groups. SXRF and TEM analyses were performed on a small number of FIB sections which act as representative samplesof primary sulfides and associated metal present in pyrrhotite-pentlandite intergrowth (PPI) grains and sulfide-rimmed metal (SRM) grains.

SXRF microprobe analyses allowed the concentrations of the minor and trace elements, Co, Cu, Ge, Zn, and Se to be quantified, in addition to Fe and Ni, at a spatial resolution of 2 µm. The similarity between the CM and CR PPI sulfide trace element patterns provides evidence for a common formation mechanism for this type of sulfide grain in both meteorite groups. In addition, the SRM sulfide and metal have comparable trace element patterns that indicates a genetic relationship between the two, such as sulfidization of metal. Enrichments in Ni, Co, Cu, and Se are consistent with the chalcophile/siderophile behavior of these elements. The observed depletions in Ge suggest that it may have been lost by evaporation or else was never incorporated into the metal or sulfide precursor materials. The depletion in Zn may also be attributable to evaporation, but, being partially lithophile, may also have been preferentially incorporated into silicates during chondrule formation. Trace element concentrations support crystallization from an immiscible sulfide melt in chondrules for formation of the PPI grains and sulfidization of metal for the origin of the SRM grains.

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

1Fahad Zaman,1Lawrence W.Townsend,2Wouter C.de Wet,1Harlan E.Spence,2Jody K.Wilson,2Nathan A.Schwadron,2Andrew P.Jordan,2Sonya S.Smith
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114629]
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 [https://doi.org/10.1016/j.gca.2021.07.011]
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.