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Vaci Z, Day JMD, Paquet M, Ziegler K, Yin QZ, Dey S, Miller A, Agee C, Bartoschewitz R, Pack A. Olivine-rich achondrites from Vesta and the missing mantle problem. Nat Commun 2021; 12:5443. [PMID: 34521838 PMCID: PMC8440560 DOI: 10.1038/s41467-021-25808-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Accepted: 07/19/2021] [Indexed: 11/09/2022] Open
Abstract
Mantles of rocky planets are dominantly composed of olivine and its high-pressure polymorphs, according to seismic data of Earth's interior, the mineralogy of natural samples, and modelling results. The missing mantle problem represents the paucity of olivine-rich material among meteorite samples and remote observation of asteroids, given how common differentiated planetesimals were in the early Solar System. Here we report the discovery of new olivine-rich meteorites that have asteroidal origins and are related to V-type asteroids or vestoids. Northwest Africa 12217, 12319, and 12562 are dunites and lherzolite cumulates that have siderophile element abundances consistent with origins on highly differentiated asteroidal bodies that experienced core formation, and with trace element and oxygen and chromium isotopic compositions associated with the howardite-eucrite-diogenite meteorites. These meteorites represent a step towards the end of the shortage of olivine-rich material, allowing for full examination of differentiation processes acting on planetesimals in the earliest epoch of the Solar System.
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Affiliation(s)
- Zoltan Vaci
- Institute of Meteoritics, University of New Mexico, Albuquerque, NM, USA.
- Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM, USA.
| | - James M D Day
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Marine Paquet
- Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
| | - Karen Ziegler
- Institute of Meteoritics, University of New Mexico, Albuquerque, NM, USA
- Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM, USA
| | - Qing-Zhu Yin
- Department of Earth and Planetary Sciences, University of California Davis, Davis, CA, USA
| | - Supratim Dey
- Department of Earth and Planetary Sciences, University of California Davis, Davis, CA, USA
| | - Audrey Miller
- Department of Earth and Planetary Sciences, University of California Davis, Davis, CA, USA
| | - Carl Agee
- Institute of Meteoritics, University of New Mexico, Albuquerque, NM, USA
- Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM, USA
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Goodrich CA, Zolensky ME, Fioretti AM, Shaddad MH, Downes H, Hiroi T, Kohl I, Young ED, Kita NT, Hamilton VE, Riebe MEI, Busemann H, Macke RJ, Fries M, Ross DK, Jenniskens P. The First Samples from Almahata Sitta Showing Contacts Between Ureilitic and Chondritic Lithologies: Implications for the Structure and Composition of Asteroid 2008 TC 3. METEORITICS & PLANETARY SCIENCE 2019; 54:2769-2813. [PMID: 33716489 PMCID: PMC7954227 DOI: 10.1111/maps.13390] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Accepted: 08/17/2019] [Indexed: 06/12/2023]
Abstract
Almahata Sitta (AhS), an anomalous polymict ureilite, is the first meteorite observed to originate from a spectrally classified asteroid (2008 TC3). However, correlating properties of the meteorite with those of the asteroid is not straightforward because the AhS stones are diverse types. Of those studied prior to this work, 70-80% are ureilites (achondrites) and 20-30% are various types of chondrites. Asteroid 2008 TC3 was a heterogeneous breccia that disintegrated in the atmosphere, with its clasts landing on Earth as individual stones and most of its mass lost. We describe AhS 91A and AhS 671, which are the first AhS stones to show contacts between ureilitic and chondritic materials and provide direct information about the structure and composition of asteroid 2008 TC3. AhS 91A and AhS 671 are friable breccias, consisting of a C1 lithology that encloses rounded to angular clasts (<10 μm to 3 mm) of olivine, pyroxenes, plagioclase, graphite, and metal-sulfide, as well as chondrules (~130-600 μm) and chondrule fragments. The C1 material consists of fine-grained phyllosilicates (serpentine and saponite) and amorphous material, magnetite, breunnerite, dolomite, fayalitic olivine (Fo 28-42), an unidentified Ca-rich silicate phase, Fe,Ni sulfides, and minor Ca-phosphate and ilmenite. It has similarities to CI1 but shows evidence of heterogeneous thermal metamorphism. Its bulk oxygen isotope composition (δ18O = 13.53‰, δ17O = 8.93‰) is unlike that of any known chondrite, but similar to compositions of several CC-like clasts in typical polymict ureilites. Its Cr isotope composition is unlike that of any known meteorite. The enclosed clasts and chondrules do not belong to the C1 lithology. The olivine (Fo 75-88), pyroxenes (pigeonite of Wo ~10 and orthopyroxene of Wo ~4.6), plagioclase, graphite, and some metal-sulfide are ureilitic, based on mineral compositions, textures, and oxygen isotope compositions, and represent at least six distinct ureilitic lithologies. The chondrules are probably derived from type 3 OC and/or CC, based on mineral and oxygen isotope compositions. Some of the metal-sulfide clasts are derived from EC. AhS 91A and AhS 671 are plausible representatives of the bulk of the asteroid that was lost. Reflectance spectra of AhS 91A are dark (reflectance ~0.04-0.05) and relatively featureless in VNIR, and have an ~2.7 μm absorption band due to OH- in phyllosilicates. Spectral modeling, using mixtures of laboratory VNIR reflectance spectra of AhS stones to fit the F-type spectrum of the asteroid, suggests that 2008 TC3 consisted mainly of ureilitic and AhS 91A-like materials, with as much as 40-70% of the latter, and <10% of OC, EC and other meteorite types. The bulk density of AhS 91A (2.35 ± 0.05 g/cm3) is lower than bulk densities of other AhS stones, and closer to estimates for the asteroid (~1.7-2.2 g/cm3). Its porosity (36%) is near the low end of estimates for the asteroid (33-50%), suggesting significant macroporosity. The textures of AhS 91A and AhS 671 (finely comminuted clasts of disparate materials intimately mixed) support formation of 2008 TC3 in a regolith environment. AhS 91A and AhS 671 could represent a volume of regolith formed when a CC-like body impacted into already well-gardened ureilitic + impactor-derived debris. AhS 91A bulk samples do not show a solar wind (SW) component, so they represent sub-surface layers. AhS 91A has a lower cosmic ray exposure (CRE) age (~5-9 Ma) than previously studied AhS stones (11-22 Ma). The spread in CRE ages argues for irradiation in a regolith environment. AhS 91A and AhS 671 show that ureilitic asteroids could have detectable ~2.7 μm absorption bands.
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Affiliation(s)
- Cyrena Anne Goodrich
- Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Blvd, Houston, TX 77058 USA
| | - Michael E Zolensky
- Astromaterials Research and Exploration Science, NASA-Johnson Space Center Houston, TX 77058 USA
| | | | - Muawia H Shaddad
- Physics Department, University of Khartoum, Khartoum 11115 Sudan
| | - Hilary Downes
- Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet Street, Bloomsbury, London WC1E 7HX UK
| | - Takahiro Hiroi
- Department of Geological Sciences, Brown University, Providence, RI 02912, USA
| | - Issaku Kohl
- Department of Earth and Planetary Sciences, University of California at Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095 USA
| | - Edward D Young
- Department of Earth and Planetary Sciences, University of California at Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095 USA
| | - Noriko T Kita
- Wisc-SIMS Laboratory, Department of Geoscience, University of Wisconsin-Madison, 1215 West Dayton Street, Madison, WI 53706 USA
| | - Victoria E Hamilton
- Department of Space Studies, Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder Colorado 80302 USA
| | - My E I Riebe
- Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Rd NW, Washington, DC 20015, USA
- Institute for Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, CH-8092 Zürich, Switzerland
| | - Henner Busemann
- Institute for Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, CH-8092 Zürich, Switzerland
| | | | - M Fries
- Astromaterials Research and Exploration Science, NASA-Johnson Space Center Houston, TX 77058 USA
| | - D Kent Ross
- Jacobs-JETS, University of Texas at El Paso, at NASA-JSC, Houston, TX 77058 USA
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Goodrich CA, Kita NT, Yin QZ, Sanborn ME, Williams CD, Nakashima D, Lane MD, Boyle S. Petrogenesis and Provenance of Ungrouped Achondrite Northwest Africa 7325 from Petrology, Trace Elements, Oxygen, Chromium and Titanium Isotopes, and Mid-IR Spectroscopy. GEOCHIMICA ET COSMOCHIMICA ACTA 2017; 203:381-403. [PMID: 30393389 PMCID: PMC6208157 DOI: 10.1016/j.gca.2016.12.021] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Northwest Africa (NWA) 7325 is an ungrouped achondrite that has recently been recognized as a sample of ancient differentiated crust from either Mercury or a previously unknown asteroid. In this work we augment data from previous investigations on petrography and mineral compositions, mid-IR spectroscopy, and oxygen isotope compositions of NWA 7325, and add constraints from Cr and Ti isotope compositions on the provenance of its parent body. In addition, we identify and discuss notable similarities between NWA 7325 and clasts of a rare xenolithic lithology found in polymict ureilites. NWA 7325 has a medium grained, protogranular to poikilitic texture, and consists of 10-15 vol. % Mg-rich olivine (Fo 98), 25-30 vol. % diopside (Wo 45, Mg# 98), 55-60 vol. % Ca-rich plagioclase (An 90), and trace Cr-rich sulfide and Fe,Ni metal. We interpret this meteorite to be a cumulate that crystallized at ≥1200 °C and very low oxygen fugacity (similar to the most reduced ureilites) from a refractory, incompatible element-depleted melt. Modeling of trace elements in plagioclase suggests that this melt formed by fractional melting or multi-stage igneous evolution. A subsequent event (likely impact) resulted in plagioclase being substantially remelted, reacting with a small amount of pyroxene, and recrystallizing with a distinctive texture. The bulk oxygen isotope composition of NWA 7325 plots in the range of ureilites on the CCAM line, and also on a mass-dependent fractionation line extended from acapulcoites. The ε54Cr and ε50Ti values of NWA 7325 exhibit deficits relative to terrestrial composition, as do ordinary chondrites and most achondrites. Its ε54Cr value is distinct from that of any analyzed ureilite, but is not resolved from that of acapulcoites (as represented by Acapulco). In terms of all these properties, NWA 7325 is unlike any known achondrite. However, a rare population of clasts found in polymict ureilites ("the magnesian anorthitic lithology") are strikingly similar to NWA 7325 in mineralogy and mineral compositions, oxygen isotope compositions, and internal textures in plagioclase. These clasts are probably xenolithic in polymict ureilites, and could be pieces of NWA 7325-like meteorites. Using constraints from chromium, titanium and oxygen isotopes, we discuss two possible models for the provenance of the NWA 7325 parent body: 1) accretion in the inner solar system from a reservoir similar to that of acapulcoites in Δ17O, ε54Cr and ε50Ti; or 2) early (< 1 Ma after CAI formation) accretion in the outer solar system (beyond the snow line), before 54Cr and 50Ti anomalies were introduced to this region of the solar system. The mid-IR emission spectrum of NWA 7325 obtained in this work matches its modal mineralogy, and so can be compared with spectra of new meteorites or asteroids/planets to help identify similar materials and/or the parent body of NWA 7325.
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Affiliation(s)
- Cyrena A Goodrich
- Lunar and Planetary Institute, 3600 Bay Area Blvd, Houston, TX 77058 USA
- Planetary Science Institute, 1700 E. Ft. Lowell Drive, Tucson, AZ 85719 USA
| | - Noriko T Kita
- WiscSIMS, University of Wisconsin-Madison, Madison, WI 53706 USA
| | - Qing-Zhu Yin
- Department of Earth and Planetary Sciences, University of California at Davis,Davis, CA 95616 USA
| | - Matthew E Sanborn
- Department of Earth and Planetary Sciences, University of California at Davis,Davis, CA 95616 USA
| | - Curtis D Williams
- Department of Earth and Planetary Sciences, University of California at Davis,Davis, CA 95616 USA
| | | | - Melissa D Lane
- Planetary Science Institute, 1700 E. Ft. Lowell Drive, Tucson, AZ 85719 USA
| | - Shannon Boyle
- Lunar and Planetary Institute, 3600 Bay Area Blvd, Houston, TX 77058 USA
- Department of Earth and Planetary Sciences, Rutgers University, Busch Campus, 610 Taylor Road, Piscataway, NJ 08854 USA
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