DOCSLIB.ORG

Physical Properties Comparison of Ordinary Chondrite Classes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Physical Properties Comparison of Ordinary Chondrite Classes 79th Annual Meeting of the Meteoritical Society (2016) 6510.pdf PHYSICAL PROPERTY COMPARISON OF ORDINARY CHONDRITE CLASSES. D. R. Ostrowski1,2 and K. L. Bryson1,2, 1NASA Ames Research Center (ARC), Moffett Field, CA, USA. E-mail: [email protected] 2BAER Institute, Ames Research Center, Moffett Field, CA, USA Introduction: Measurements of the physical properties of meteorites are essential in helping to determine the physical characteristics of the parent asteroids. The study of physical properties can provide fundamental infor- mation to understand meteoroid behavior in the atmosphere and determine methods to deflect potentially hazardous asteroids. A diverse selection of over 45 classes of meteorites has entered the atmosphere [1]. Ordinary chondrites and iron meteorites are more important to planetary defense because of their quantity and likelihood of reaching the ground. The initial focus of our study is on ordinary chondrites, since they are over 70% of the meteorites [2]. Experimental: To date we have measured the density (both bulk and grain), porosity, thermal emissivity, and acoustic velocity of seven ordinary chondrites. Each meteorite is first weighed and laser 3D scanned using a Nex- tEngine scanner to determine the Bulk density. For the other tests 1.5cm cubes of the meteorites are studied. Grain density is determined using a Quantachrome gas pycnometer using nitrogen gas displacement. Porosity is calculated from bulk and grain densities. Acoustic velocity, both longitudinal and shear wave, are measured using an Olympus 45-MG meter in single element mode. This allows for the calculation of both the Young’s and Shear moduli. Thermal emissivity is measured from 20°C up to atmospheric entry temperatures. Emissivity data is based on aver- age measurements over the wavelength range of 8 to 14 µm. Physical Properties Data: Density and Porosity. The average bulk density of ordinary chondrites is 3-4 g/cm3, stony-irons is 4-6 g/cm3, and irons is 7-8 g/cm3 [3]. Of the studied meteorites, Tamdakht is an average H chondrite. Chelyabinsk and the studied Antarctic meteorites have lower bulk and higher grain densities yielding above average porosities (Fig 1). Acoustic Velocity. Tamdakht has a lower longitudinal velocity of 1.14±0.04 mm/µs than the normal rage for H chondrites at 2.66-6.99 mm/µs. The velocity is consistent across all three axes in the sample. One possibility for this is an internal fracture, where part of has been observed on the surface of one of the test cubes. Emissivity. Calculated emissivity range for ordinary chondrites is 0.984 to 0.991 at 20 °C [4]. Figure 2 displays our measured emissivities. Tamdakht is on the high end of the emissivity range for H chondrites and Chelyabinsk is on the high end for LL chondrites. BTN 00304 has the highest average over the temperature range, while ALHA77294 has the lowest average. Emissivity of the heated samples decreases slightly from initial 20 °C meas- urement, Thamdakht varies the least up to near 200 °C within error. Conclusion: The properties of density, porosity and emissivity (at 20 °C) for Tamdakht match it to a typical H ordinary chondrite, but has a lower then average longitudinal wave velocity. An internal fracture in the cube is most likely the cause of some of the reduced acoustic velocity. As expected the Antarctic meteorites have a higher poros- ity than the average of their types because of increased grain density from weathering. Thermal emissivity, between 40-200 °C, stays constant at a slight decrease value from room temperature. References: [1] Sears D.W.G. et al. (2016) Proceedings of the AIAA SciTech, AIAA-2016-0997. [2] Grady M. M. (2000) Catalogue Meteorites, 5th ed., Cambridge University Press. [3] Vernazza P. et al. 2012. Icarus 221:1162- 1172. [4] Baldridge A. M. et al. (2009) Remote Sensing of Environment, 113, 711-715. Acknowledgements: We acknowledge the support of NASA’s NEO program, Jim Arnold for leading the Asteroid Threat Assessment Project at ARC, Derek Sears for support and discussion. Figure 1. Bulk and grain density and porosity comparison to Figure 2. Low temperature emissivity data for meteorites, iron ordinary chondrite averages. and basalt. General emissivity for H chondrites 0.989±0.002, L chondrite 0.987±0.002, and LL chondrites 0.987±0.002..
Load more

Recommended publications
  • Hf–W Thermochronometry: II. Accretion and Thermal History of the Acapulcoite–Lodranite Parent Body
    Earth and Planetary Science Letters 284 (2009) 168–178 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl Hf–W thermochronometry: II. Accretion and thermal history of the acapulcoite–lodranite parent body Mathieu Touboul a,⁎, Thorsten Kleine a, Bernard Bourdon a, James A. Van Orman b, Colin Maden a, Jutta Zipfel c a Institute of Isotope Geochemistry and Mineral Resources, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland b Department of Geological Sciences, Case Western Reserve University, Cleveland, OH, USA c Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt am Main, Germany article info abstract Article history: Acapulcoites and lodranites are highly metamorphosed to partially molten meteorites with mineral and bulk Received 11 November 2008 compositions similar to those of ordinary chondrites. These properties place the acapulcoites and lodranites Received in revised form 8 April 2009 between the unmelted chondrites and the differentiated meteorites and as such acapulcoites–lodranites are Accepted 9 April 2009 of special interest for understanding the initial stages of asteroid differentiation as well as the role of 26Al Available online 3 June 2009 heating in the thermal history of asteroids. To constrain the accretion timescale and thermal history of the Editor: R.W. Carlson acapulcoite–lodranite parent body, and to compare these results to the thermal histories of other meteorite parent bodies, the Hf–W system was applied to several acapulcoites and lodranites. Acapulcoites Dhofar 125 Keywords: – Δ chronology and NWA 2775 and lodranite NWA 2627 have indistinguishable Hf W ages of tCAI =5.2±0.9 Ma and Δ isochron tCAI =5.7±1.0 Ma, corresponding to absolute ages of 4563.1±0.8 Ma and 4562.6±0.9 Ma.
    [Show full text]
  • Petrography and Mineral Chemistry of Escalón Meteorite, an H4 Chondrite, México
    148 Reyes-SalasRevista Mexicana et al. de Ciencias Geológicas, v. 27, núm. 1, 2010, p. 148-161 Petrography and mineral chemistry of Escalón meteorite, an H4 chondrite, México Adela M. Reyes-Salas1,*, Gerardo Sánchez-Rubio1, Patricia Altuzar-Coello2, Fernando Ortega-Gutiérrez1, Daniel Flores-Gutiérrez3, Karina Cervantes-de la Cruz1, Eugenio Reyes4, and Carlos Linares5 1 Universidad Nacional Autónoma de México, Instituto de Geología, Del. Coyoacán, 04510 México D.F., Mexico. 2 Universidad Nacional Autónoma de México, Centro de Investigación en Energía, Campus Temixco, Priv. Xochicalco s/n, 62580 Temixco Morelos, Mexico. 3 Universidad Nacional Autónoma de México, Instituto de Astronomía, Del. Coyoacán, 04510 México D.F., Mexico. 4 Universidad Nacional Autónoma de México, Facultad de Química, Del. Coyoacán, 04510 México D.F., Mexico. 5 Universidad Nacional Autónoma de México, Instituto de Geofísica, Del. Coyoacán, 04510 México D.F., Mexico. * [email protected] ABSTRACT The Escalón meteorite, a crusted mass weighing 54.3 g, was recovered near Zona del Silencio in Escalón, state of Chihuahua, México. The stone is an ordinary chondrite belonging to the high iron group H, type 4. Electron microprobe analyses of olivine (Fa18.1) and pyroxene (Fs16.5), phosphate, plagioclase, opaque phases, matrix and chondrule glasses are presented. The metal phases present are kamacite (6.08 % Ni), taenite (31.66 % Ni), high nickel taenite (50.01 % Ni) and traces of native Cu. The chondrules average apparent diameter measures 0.62 mm. X-ray diffraction pattern shows olivine, pyroxene and kamacite. Alkaline-type glass is found mainly in chondrules. This meteorite is a stage S3, shock-blackened chondrite with weathering grade W0.
    [Show full text]
  • Zinc and Copper Isotopic Fractionation During Planetary Differentiation Heng Chen Washington University in St
    Washington University in St. Louis Washington University Open Scholarship Arts & Sciences Electronic Theses and Dissertations Arts & Sciences Winter 12-15-2014 Zinc and Copper Isotopic Fractionation during Planetary Differentiation Heng Chen Washington University in St. Louis Follow this and additional works at: https://openscholarship.wustl.edu/art_sci_etds Part of the Earth Sciences Commons Recommended Citation Chen, Heng, "Zinc and Copper Isotopic Fractionation during Planetary Differentiation" (2014). Arts & Sciences Electronic Theses and Dissertations. 360. https://openscholarship.wustl.edu/art_sci_etds/360 This Dissertation is brought to you for free and open access by the Arts & Sciences at Washington University Open Scholarship. It has been accepted for inclusion in Arts & Sciences Electronic Theses and Dissertations by an authorized administrator of Washington University Open Scholarship. For more information, please contact [email protected]. WASHINGTON UNIVERSITY IN ST. LOUIS Department of Earth and Planetary Sciences Dissertation Examination Committee: Bradley L. Jolliff, Chair Jeffrey G. Catalano Bruce Fegley, Jr. Michael J. Krawczynski Frédéric Moynier Zinc and Copper Isotopic Fractionation during Planetary Differentiation by Heng Chen A dissertation presented to the Graduate School of Arts & Sciences of Washington University in partial fulfillment of the requirements for the degree of Doctor of Philosophy December 2014 St. Louis, Missouri Copyright © 2014, Heng Chen All rights reserved. Table of Contents LIST OF FIGURES
    [Show full text]
  • Chondrule Sizes, We Have Compiled and Provide Commentary on Available Chondrule Dimension Literature Data
    Invited review Chondrule size and related physical properties: a compilation and evaluation of current data across all meteorite groups. Jon M. Friedricha,b,*, Michael K. Weisbergb,c,d, Denton S. Ebelb,d,e, Alison E. Biltzf, Bernadette M. Corbettf, Ivan V. Iotzovf, Wajiha S. Khanf, Matthew D. Wolmanf a Department of Chemistry, Fordham University, Bronx, NY 10458 USA b Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY 10024 USA c Department of Physical Sciences, Kingsborough College of the City University of New York, Brooklyn, NY 11235, USA d Graduate Center of the City University of New York, 365 5th Ave, New York, NY 10016 USA e Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964 USA f Fordham College at Rose Hill, Fordham University, Bronx, NY 10458 USA In press in Chemie der Erde – Geochemistry 21 August 2014 *Corresponding Author. Tel: +718 817 4446; fax: +718 817 4432. E-mail address: [email protected] 2 ABSTRACT The examination of the physical properties of chondrules has generally received less emphasis than other properties of meteorites such as their mineralogy, petrology, and chemical and isotopic compositions. Among the various physical properties of chondrules, chondrule size is especially important for the classification of chondrites into chemical groups, since each chemical group possesses a distinct size-frequency distribution of chondrules. Knowledge of the physical properties of chondrules is also vital for the development of astrophysical models for chondrule formation, and for understanding how to utilize asteroidal resources in space exploration. To examine our current knowledge of chondrule sizes, we have compiled and provide commentary on available chondrule dimension literature data.
    [Show full text]
  • Petrogenesis of Acapulcoites and Lodranites: a Shock-Melting Model
    Geochimica et Cosmochimica Acta 71 (2007) 2383–2401 www.elsevier.com/locate/gca Petrogenesis of acapulcoites and lodranites: A shock-melting model Alan E. Rubin * Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, USA Received 31 May 2006; accepted in revised form 20 February 2007; available online 23 February 2007 Abstract Acapulcoites are modeled as having formed by shock melting CR-like carbonaceous chondrite precursors; the degree of melting of some acapulcoites was low enough to allow the preservation of 3–6 vol % relict chondrules. Shock effects in aca- pulcoites include veins of metallic Fe–Ni and troilite, polycrystalline kamacite, fine-grained metal–troilite assemblages, metal- lic Cu, and irregularly shaped troilite grains within metallic Fe–Ni. While at elevated temperatures, acapulcoites experienced appreciable reduction. Because graphite is present in some acapulcoites and lodranites, it seems likely that carbon was the principal reducing agent. Reduction is responsible for the low contents of olivine Fa (4–14 mol %) and low-Ca pyroxene Fs (3–13 mol %) in the acapulcoites, the observation that, in more than two-thirds of the acapulcoites, the Fa value is lower than the Fs value (in contrast to the case for equilibrated ordinary chondrites), the low FeO/MnO ratios in acapulcoite olivine (16–18, compared to 32–38 in equilibrated H chondrites), the relatively high modal orthopyroxene/olivine ratios (e.g., 1.7 in Monument Draw compared to 0.74 in H chondrites), and reverse zoning in some mafic silicate grains. Lodranites formed in a similar manner to acapulcoites but suffered more extensive heating, loss of plagioclase, and loss of an Fe–Ni–S melt.
    [Show full text]
  • The Hamburg Meteorite Fall: Fireball Trajectory, Orbit and Dynamics
    The Hamburg Meteorite Fall: Fireball trajectory, orbit and dynamics P.G. Brown1,2*, D. Vida3, D.E. Moser4, M. Granvik5,6, W.J. Koshak7, D. Chu8, J. Steckloff9,10, A. Licata11, S. Hariri12, J. Mason13, M. Mazur3, W. Cooke14, and Z. Krzeminski1 *Corresponding author email: [email protected] ORCID ID: https://orcid.org/0000-0001-6130-7039 1Department of Physics and Astronomy, University of Western Ontario, London, Ontario, N6A 3K7, Canada 2Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario, N6A 5B7, Canada 3Department of Earth Sciences, University of Western Ontario, London, Ontario, N6A 3K7, Canada ( 4Jacobs Space Exploration Group, EV44/Meteoroid Environment Office, NASA Marshall Space Flight Center, Huntsville, AL 35812 USA 5Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland 6 Division of Space Technology, Luleå University of Technology, Kiruna, Box 848, S-98128, Sweden 7NASA Marshall Space Flight Center, ST11, Robert Cramer Research Hall, 320 Sparkman Drive, Huntsville, AL 35805, USA 8Chesapeake Aerospace LLC, Grasonville, MD 21638, USA 9Planetary Science Institute, Tucson, AZ, USA 10Department of Aerospace Engineering and Engineering Mechanics, University of Texas at Austin, Austin, TX, USA 11Farmington Community Stargazers, Farmington Hills, MI, USA 12Department of Physics and Astronomy, Eastern Michigan University, Ypsilanti, MI, USA 13Orchard Ridge Campus, Oakland Community College, Farmington Hills, MI, USA 14NASA Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Alabama 35812, USA Accepted to Meteoritics and Planetary Science, June 19, 2019 85 pages, 4 tables, 15 figures, 1 appendix. Original submission September, 2018. 1 Abstract The Hamburg (H4) meteorite fell on January 17, 2018 at 01:08 UT approximately 10km North of Ann Arbor, Michigan.
    [Show full text]
  • March 21–25, 2016
    FORTY-SEVENTH LUNAR AND PLANETARY SCIENCE CONFERENCE PROGRAM OF TECHNICAL SESSIONS MARCH 21–25, 2016 The Woodlands Waterway Marriott Hotel and Convention Center The Woodlands, Texas INSTITUTIONAL SUPPORT Universities Space Research Association Lunar and Planetary Institute National Aeronautics and Space Administration CONFERENCE CO-CHAIRS Stephen Mackwell, Lunar and Planetary Institute Eileen Stansbery, NASA Johnson Space Center PROGRAM COMMITTEE CHAIRS David Draper, NASA Johnson Space Center Walter Kiefer, Lunar and Planetary Institute PROGRAM COMMITTEE P. Doug Archer, NASA Johnson Space Center Nicolas LeCorvec, Lunar and Planetary Institute Katherine Bermingham, University of Maryland Yo Matsubara, Smithsonian Institute Janice Bishop, SETI and NASA Ames Research Center Francis McCubbin, NASA Johnson Space Center Jeremy Boyce, University of California, Los Angeles Andrew Needham, Carnegie Institution of Washington Lisa Danielson, NASA Johnson Space Center Lan-Anh Nguyen, NASA Johnson Space Center Deepak Dhingra, University of Idaho Paul Niles, NASA Johnson Space Center Stephen Elardo, Carnegie Institution of Washington Dorothy Oehler, NASA Johnson Space Center Marc Fries, NASA Johnson Space Center D. Alex Patthoff, Jet Propulsion Laboratory Cyrena Goodrich, Lunar and Planetary Institute Elizabeth Rampe, Aerodyne Industries, Jacobs JETS at John Gruener, NASA Johnson Space Center NASA Johnson Space Center Justin Hagerty, U.S. Geological Survey Carol Raymond, Jet Propulsion Laboratory Lindsay Hays, Jet Propulsion Laboratory Paul Schenk,
    [Show full text]
  • [802] PRINT ONLY: CHONDRITES and THEIR COMPONENTS Berzin S. V. Erokhin Yu. V. Khiller V. V. Ivanov K. S. Variations in Th
    47th Lunar and Planetary Science Conference (2016) sess802.pdf [802] PRINT ONLY: CHONDRITES AND THEIR COMPONENTS Berzin S. V. Erokhin Yu. V. Khiller V. V. Ivanov K. S. Variations in the Chemical Composition of Pentlandite in Different Ordinary Chondrites [#1056] The chemical composition properties of pentlandite from different ordinary chondrites was studied. Caporali S. Moggi-Cecchi V. Pratesi G. Franchi I. A. Greenwood R. C. Textural and Minerochemical Features of Dar al Gani 1067, a New CK Chondrite from Libya [#2016] This communication describes the chemical, petrological, and oxygen isotopic features of a newly approved carbonaceous chondrite from the Dar al Gani region (Libya). Cortés-Comellas J. Trigo-Rodríguez J. M. Llorca J. Moyano-Cambero C. E. UV-NIR Reflectance Spectra of Ordinary Chondrites to Better Understand Space Weathering Effects in S-Class Asteroids [#2610] We compare the UV-NIR spectra of S-type asteroids with several L and H ordinary chondrites, in order to better understand space weathering effects on spectra. Fisenko A. V. Semjonova L. F. Kinetics of C, N, Ar, and Xe Release During Combustion of the Small Metal-Sulphide Intergrows of Saratov (L4) Meteorite [#1071] It’s shown the metal-sulphide intergrows of Saratov chondrite contains Ar and Xe. They either are dissolved in pentlandite or are in its carbonaceous inclusions. Kalinina G. V. Pavlova T. A. Alexeev V. A. Some Features of the Distribution of VH-Nuclei Tracks of Galactic Cosmic Rays in Ordinary Chondrites [#1019] The tendency of decreasing of the average rate of track formation with increasing of cosmic ray exposure ages of meteorites is found and discussed.
    [Show full text]
  • Marek ZBIK1,2, Peter SELF3
    MINERALOGIA POLONICA Vol. 36, No 1, 2005 PL ISSN 0032-6267 Marek ZBIK1,2, Peter SELF3 HIGH RESOLUTION X-RAY MICROTOMOGRAPHY ANALYSIS IN NON-DESTRUCTIVE INVESTIGATION OF INTERNAL STRUCTURE IN TWO CHONDRITES Abstract.Acomparison of the internal structure of two stony meteorites has been carried out using computer-aided X-ray microtomography (X-ray CT). The meteorites are both chondrites of the petrological type 5 with one (Baszkowka) being a group L chondrite and the other (Pultusk) being a group H chondrite. The volume of metal grains in the Pultusk meteorite (7.7 vol.%) is larger than that in the Baszkowka meteorite (5.1 vol.%). The metal grains in the Baszkowka meteorite are generally larger than those in the Pultusk meteorite. The Baszkowka meteorite has a much higher void volume (8.7 vol.%) than the Pultusk meteorite (3.4 vol.%). The voids in the Pultusk meteorite are generally much smaller than the voids in the Baszkowka meteorite. X-ray CT shows that the two meteorites, despite being structurally different, reveal in each similar correlations between the structural characteristics of the metal grains and voids. From an analysis of the structural features of both meteorites it is postulated that more regularly shaped intergranular voids were formed at the same time as the regularly shaped metal and silicate grains. It means they had formed when the meteorite parent body had been assembled, i.e. before metamorphism inside the meteorite parent bodies. It is also postulated that the less porous, high aspect ratio void systems seen in the Pultusk meteorite (elongated, fissures) formed after pressure metamorphic period and during a shock event that fragmented the parent body of this meteorite.
    [Show full text]
  • Spade: an H Chondrite Impact-Melt Breccia That Experienced Post-Shock Annealing
    Meteoritics & Planetary Science 38, Nr 10, 1507–1520 (2003) Abstract available online at http://meteoritics.org Spade: An H chondrite impact-melt breccia that experienced post-shock annealing Alan E. RUBIN 1* and Rhian H. JONES 2 1Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095–1567, USA 2Institute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA *Corresponding author. E-mail: [email protected] (Received 26 January 2003; revision accepted 19 October 2003) Abstract–The low modal abundances of relict chondrules (1.8 vol%) and of coarse (i.e., ³200 mm- size) isolated mafic silicate grains (1.8 vol%) in Spade relative to mean H6 chondrites (11.4 and 9.8 vol%, respectively) show Spade to be a rock that has experienced a significant degree of melting. Various petrographic features (e.g., chromite-plagioclase assemblages, chromite veinlets, silicate darkening) indicate that melting was caused by shock. Plagioclase was melted during the shock event and flowed so that it partially to completely surrounded nearby mafic silicate grains. During crystallization, plagioclase developed igneous zoning. Low-Ca pyroxene that crystallized from the melt (or equilibrated with the melt at high temperatures) acquired relatively high amounts of CaO. Metallic Fe-Ni cooled rapidly below the Fe-Ni solvus and transformed into martensite. Subsequent reheating of the rock caused transformation of martensite into abundant duplex plessite. Ambiguities exist in the shock stage assignment of Spade. The extensive silicate darkening, the occurrence of chromite-plagioclase assemblages, and the impact-melted characteristics of Spade are consistent with shock stage S6.
    [Show full text]
  • The Origin and History of Ordinary Chondrites: a Study by Iron Isotope Measurements of Metal Grains from Ordinary Chondrites
    Available online at www.sciencedirect.com Geochimica et Cosmochimica Acta 72 (2008) 4440–4456 www.elsevier.com/locate/gca The origin and history of ordinary chondrites: A study by iron isotope measurements of metal grains from ordinary chondrites K.J. Theis a,*, R. Burgess a, I.C. Lyon a, D.W. Sears b a School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester M13 9PL, UK b Arkansas Center for Space and Planetary Science and Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA Received 15 August 2007; accepted in revised form 30 May 2008; available online 14 June 2008 Abstract Chondrules and chondrites provide unique insights into early solar system origin and history, and iron plays a critical role in defining the properties of these objects. In order to understand the processes that formed chondrules and chondrites, and introduced isotopic fractionation of iron isotopes, we measured stable iron isotope ratios 56Fe/54Fe and 57Fe/54Fe in metal grains separated from 18 ordinary chondrites, of classes H, L and LL, ranging from petrographic types 3–6 using multi-col- lector inductively coupled plasma mass spectrometry. The d56Fe values range from À0.06 ± 0.01 to +0.30 ± 0.04& and d57Fe values are À0.09 ± 0.02 to +0.55 ± 0.05& (relative to IRMM-014 iron isotope standard). Where comparisons are possible, these data are in good agreement with published data. We found no systematic difference between falls and finds, suggesting that terrestrial weathering effects are not important in controlling the isotopic fractionations in our samples.
    [Show full text]
  • Finegrained Precursors Dominate the Micrometeorite Flux
    Meteoritics & Planetary Science 47, Nr 4, 550–564 (2012) doi: 10.1111/j.1945-5100.2011.01292.x Fine-grained precursors dominate the micrometeorite flux Susan TAYLOR1*, Graciela MATRAJT2, and Yunbin GUAN3 1Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, New Hampshire 03755–1290, USA 2University of Washington, Seattle, Washington 98105, USA 3Geological & Planetary Sciences MC 170-25, Caltech, Pasadena, California 91125, USA *Corresponding author. E-mail: [email protected] (Received 15 May 2011; revision accepted 22 September 2011) Abstract–We optically classified 5682 micrometeorites (MMs) from the 2000 South Pole collection into textural classes, imaged 2458 of these MMs with a scanning electron microscope, and made 200 elemental and eight isotopic measurements on those with unusual textures or relict phases. As textures provide information on both degree of heating and composition of MMs, we developed textural sequences that illustrate how fine-grained, coarse-grained, and single mineral MMs change with increased heating. We used this information to determine the percentage of matrix dominated to mineral dominated precursor materials (precursors) that produced the MMs. We find that at least 75% of the MMs in the collection derived from fine-grained precursors with compositions similar to CI and CM meteorites and consistent with dynamical models that indicate 85% of the mass influx of small particles to Earth comes from Jupiter family comets. A lower limit for ordinary chondrites is estimated at 2–8% based on MMs that contain Na-bearing plagioclase relicts. Less than 1% of the MMs have achondritic compositions, CAI components, or recognizable chondrules. Single mineral MMs often have magnetite zones around their peripheries.
    [Show full text]