D. S. Ebel

Lamont - Doherty Earth Observatory Columbia University, New York, New York, United States

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Publications (259)609.23 Total impact

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    ABSTRACT: We report on a suite of microchondrules from three unequilibrated ordinary chondrites (UOCs). Microchondrules, a subset of chondrules that are ubiquitous components of UOCs, commonly occur in fine-grained chondrule rims, although may also occur within matrix. Microchondrules have a variety of textures: cryptocrystalline, microporphyritic, radial, glassy. In some cases, their textures, and in many cases, their compositions, are similar to their larger host chondrules. Bulk compositions for both chondrule populations frequently overlap. The primary material that composes many of the microchondrules has compositions that are pyroxene-normative and is similar to low-Ca-pyroxene phenocrysts from host chondrules; primary material rarely resembles olivine or plagioclase. Some microchondrules are composed of FeO-rich material that has compositions similar to the bulk submicron fine-grained rim material. These microchondrules, however, are not a common compositional type and probably represent secondary FeO-enrichment. Microchondrules may also be porous, suggestive of degasing to form vesicles. Our work shows that the occurrence of microchondrules in chondrule rims is an important constraint that needs to be considered when evaluating chondrule-forming mechanisms. We propose that microchondrules represent melted portions of the chondrule surfaces and/or the melt products of coagulated dust in the immediate vicinity of the larger chondrules. We suggest that, through recycling events, the outer surfaces of chondrules were heated enough to allow microchondrules to bud off as protuberances and become entrained in the surrounding dusty environment as chondrules were accreting fine-grained rims. Microchondrules are thus byproducts of cyclic processing of chondrules in localized environments. Their occurrence in fine-grained rims represents a snapshot of the chondrule-forming environment. We evaluate mechanisms for microchondrule formation and hypothesize a potential link between the emergence of type II chondrules in the early solar system and the microchondrule-bearing fine-grained rims surrounding type I chondrules.
    No preview · Article · Jan 2016 · Meteoritics & planetary science
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    ABSTRACT: The relative abundances and chemical compositions of the macroscopic components or "inclusions" (chondrules and refractory inclusions) and fine-grained mineral matrix in chondritic meteorites provide constraints on astrophysical theories of inclusion formation and chondrite accretion. We present new techniques for analysis of low count/pixel Si, Mg, Ca, Al, Ti and Fe X-ray intensity maps of rock sections, and apply them to large areas of CO and CV chondrites, and the ungrouped Acfer 094 chondrite. For many thousands of manually segmented and type-identified inclusions, we are able to assess, pixel-by-pixel, the major element content of each inclusion. We quantify the total fraction of refractory elements accounted for by various types of inclusion and matrix. Among CO chondrites, both matrix and inclusion Mg/Si ratios approach the solar (and bulk CO) ratio with increasing petrologic grade, but Si remains enriched in inclusions relative to matrix. The oxidized CV chondrites with higher matrix/inclusion ratios exhibit more severe aqueous alteration (oxidation), and their excess matrix accounts for their higher porosity relative to reduced CV chondrites. Porosity could accommodate an original ice component of matrix as the direct cause of local alteration of oxidized CV chondrites. We confirm that major element abundances among inclusions differ greatly, across a wide range of CO and CV chondrites. These abundances in all cases add up to near-chondritic (solar) bulk abundance ratios in these chondrites, despite wide variations in matrix/inclusion ratios and inclusion sizes: chondrite components are complementary. This complementarity provides a robust meteoritic constraint for astrophysical disk models.
    No preview · Article · Jan 2016 · Geochimica et Cosmochimica Acta
  • D. S. Ebel · E. J. Crapster-Pregont · A. Lobo

    No preview · Conference Paper · Aug 2015

  • No preview · Conference Paper · Aug 2015
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    ABSTRACT: Northwest Africa (NWA) 5492 and Grosvenor Mountains (GRO) 95551 are metal-rich chondrites having silicate (olivine and pyroxene) compositions that are more reduced than those in other metal-rich chondrites, such as the CH and CB chondrites. Additionally, sulfides in NWA 5492 and GRO 95551 are more abundant and not related to the metal, as in the CB chondrites. Average metal compositions in NWA 5492 and GRO 95551 are close to H chondrite metal. Oxygen isotope ratios of NWA 5492 and GRO 95551 components (chondrules and fragments) show a range of compositions with most having δ17O values >0‰. Since there is no matrix component, their average chondrule+fragment oxygen isotopic compositions are considered to be representative of whole rock and (δ17O values) are sandwiched between the values for enstatite (E) and ordinary (O) chondrites. These data argue for a close relationship between NWA 5492 and GRO 95551 and suggest that they are the first examples of a new type of metal-rich chondrite.Oxygen isotope ratios of chondrules in NWA 5492 and GRO 95551 show considerable overlap with chondrules in O, E and R chondrites, with average compositions indistinguishable from LL3 chondrules, suggesting considerable mixing between these Solar System materials during chondrule formation and/or that their precursors experienced similar formation environments and/or processes. Another characteristic shared between NWA 5492 and GRO 95551 and O, E and R chondrites is that they are all relatively dry (low abundances of hydrated minerals), compared to many C chondrites and have fewer, smaller CAIs than many C chondrites. (No CAIs were found in NWA 5492 or GRO 95551 but they contain rare Al-rich chondrules.) We suggest that O, E, R and the NWA 5492 and GRO 95551 chondrites are closely related Solar System materials.
    Full-text · Article · Jul 2015 · Geochimica et Cosmochimica Acta
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    ABSTRACT: Orbital measurements obtained by the MESSENGER Gamma-Ray Spectrometer have been analyzed to determine the surface abundance of chlorine in Mercury’s northern hemisphere. The derived Cl/Si mass ratio is 0.0057 ± 0.001, which for an assumed Si abundance of 24.6 wt% corresponds to 0.14 ± 0.03 wt% Cl. The abundance of Cl is a factor of 2.9 ± 1.3 higher in the north polar region (>80°N) than at latitudes 0−60°N, a latitudinal variation similar to that observed for Na. Our reported Cl abundances are consistent with measured bulk concentrations of neutron-absorbing elements on Mercury, particularly those observed at high northern latitudes. The Cl/K ratio on Mercury is chondritic, indicating a limited impact history akin to that of Mars, which accreted rapidly. Hypotheses for the origin of Mercury’s high metal-to-silicate ratio must be able to reproduce Mercury’s observed elemental abundances, including Cl. Chlorine is also an important magmatic volatile, and its elevated abundance in the northern polar region of Mercury indicates that it could have played a role in the production, ascent, and eruption of flood volcanic material in this region. We have identified several candidate primary mineralogical hosts for Cl on Mercury, including the halide minerals lawrencite (FeCl2), sylvite (KCl), and halite (NaCl), as well as Cl-bearing alkali sulfides. Amphiboles, micas, apatite, and aqueously deposited halides, in contrast, may be ruled out as mineralogical hosts of Cl on Mercury.
    No preview · Article · May 2015 · Icarus
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    ABSTRACT: We have mapped the major-element composition of Mercury's surface from orbital MESSENGER X-Ray Spectrometer measurements. These maps constitute the first global-scale survey of the surface composition of a Solar System body conducted with the technique of planetary X-ray fluorescence. Full maps of Mg and Al, together with partial maps of S, Ca, and Fe, each relative to Si, reveal highly variable compositions (e.g., Mg/Si and Al/Si range over 0.1–0.8 and 0.1–0.4, respectively). The geochemical variations that we observe are consistent with those inferred from other MESSENGER geochemical remote sensing datasets, but they do not correlate well with units mapped previously from spectral reflectance or morphology. Location-dependent, rather than temporally evolving, partial melt sources were likely the major influence on the compositions of the magmas that produced different geochemical terranes. A large ( ) region with the highest Mg/Si, Ca/Si, and S/Si ratios, as well as relatively thin crust, may be the site of an ancient and heavily degraded impact basin. The distinctive geochemical signature of this region could be the consequence of high-degree partial melting of a reservoir in a vertically heterogeneous mantle that was sampled primarily as a result of the impact event.
    No preview · Article · Apr 2015 · Earth and Planetary Science Letters
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    G Ustunisik · D S Ebel · D Walker
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    ABSTRACT: Introduction: Ca-, Al-rich inclusions (CAIs) in chondrite meteorites are the oldest crystalline solids in the solar system. Therefore, the variations of trace element concentrations within individual CAIs can provide crucial information into the nature of processes effective in the primitive solar nebula. Despite most CAIs having complex histories during and after their initial formation [1], high-temperature, Type B (igne-ous) CAIs [2, 3] offer a unique opportunity to understand the distribution of trace elements in a controlled magmatic system which underwent fractional crystalli-zation from a single starting liquid of a known bulk composition, crystallization sequence [4], and approximately known cooling rate [5, 6]. The mineralogy of Type B CAIs is dominated by refractory oxides and silicates such as spinel, melilite, Al-, Ti-bearing clinopyroxene, and grossite. These minerals are among the first solids predicted to condense from a hot cooling gas of solar composition [3,7] and therefore the trace element abundances and distribution among these minerals can reveal information about the processes of CAI formation including the role of volatilization, fractional condensation, and fractional crystallization. However, the accurate assessment of how Type B CAIs crystallized requires knowledge of the appropriate mineral–melt partition coefficients. While fairly extensive analytical data exists on trace element partitioning between certain phases (anorthite, clinopyroxene, hibonite, perovskite, and melilite) and CAI type melts, partition coefficients are very sparse for spinels-especially at various oxygen fugacities; and completely missing for rarer phases such as gros-site [8]. Furthermore, previous experimental partitioning data is only available for certain trace elements and is limited to phases such as melilite, perovskite, spinel, and diopside [9-12] and to a single bulk liquid composition. Here, we designed crystallization experiments using various bulk compositions from [13] to determine partitioning of trace and REEs in specific fields of condensation space (Fig. 1) between grossite, melilite and CAI-type liquids. These results will provide systematic constraints on compositional, temperature, and oxygen fugacity dependence of trace and REE partitioning between solids and CAI-type liquids. This abstract reports only on preliminary experiments on the partitioning of trace elements and REEs between grossite and CAI-type liquids.
    Full-text · Conference Paper · Mar 2015
  • G. Ustunisik · D. S. Ebel · D. Walker
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    ABSTRACT: Trace-element partitioning experiments between grossite and CAI-type melts reveal that REEs, HFSEs (Zr, Nb, Hf, Ta, Th), and LILE (B) are incompatible in grossite.
    No preview · Article · Feb 2015
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    ABSTRACT: Orientation and textural analysis of multiple, concentric metal layers in a layered chondrule from Acfer 139 yielding chondrule formation constraints.
    No preview · Article · Feb 2015
  • A. Hubbard · D. S. Ebel
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    ABSTRACT: We offer a model that explains Earth's volatile depletion pattern by baking dust and thermally altering its aerodynamics through accretion events such as FUors.
    No preview · Article · Feb 2015
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    Herbert Palme · Dominik C. Hezel · Denton S. Ebel
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    ABSTRACT: One of the major unresolved problems in cosmochemistry is the origin of chondrules, once molten, spherical silicate droplets with diameters of 0.2 to 2 mm. Chondrules are an essential component of primitive meteorites and perhaps of all early solar system materials including the terrestrial planets. Numerous hypotheses have been proposed for their origin. Many carbonaceous chondrites are composed of about equal amounts of chondrules and fine-grained matrix. Recent data confirm that matrix in carbonaceous chondrites has high Si/Mg and Fe/Mg ratios when compared to bulk carbonaceous chondrites with solar abundance ratios. Chondrules have the opposite signature, low Si/Mg and Fe/Mg ratios. In some carbonaceous chondrites chondrules have low Al/Ti ratios, matrix has the opposite signature and the bulk is chondritic. It is shown in detail that these complementary relationships cannot have evolved on the parent asteroid(s) of carbonaceous chondrites. They reflect preaccretionary processes. Both chondrules and matrix must have formed from a single, solar-like reservoir. Consequences of complementarity for chondrule formation models are discussed. An independent origin and/or random mixing of chondrules and matrix can be excluded. Hence, complementarity is a strong constraint for all astrophysical–cosmochemical models of chondrule formation. Although chondrules and matrix formed from a single reservoir, the chondrule-matrix system was open to the addition of oxygen and other gaseous components.Keywordschondrulesmatrixcarbonaceous chondritescomplementarity chondrule matrixformation of chondrules
    Full-text · Article · Feb 2015 · Earth and Planetary Science Letters
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    Full-text · Dataset · Jan 2015
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    ABSTRACT: We examined the Al-Mg isotope systematics of plagioclase in a FeO-poor ferromagnesian Wild 2 particle (C2092,7,81,1,0; named Pyxie) using a ∼2 μm spot. Three analyses show average 27Al/24Mg ratio of ∼65 and excess δ26Mg⁎ value of + 0.1 ± 4.5 ‰ (2σ), indicating no resolvable 26Mg excess in the particle. The inferred initial (26Al/27Al)0 ratio of plagioclase in Pyxie is estimated as (- 0.6 ± 4.5) ×10-6 with an upper limit of 4 ×10-6. The result is very similar to that of the FeO-rich ferromagnesian particle “Iris” (Ogliore et al., 2012). Assuming homogeneous distribution of 26Al in the early solar system, Pyxie formed at least 2.6 Ma after the oldest Ca-Al-rich inclusions. This minimum formation age is marginally younger than formation ages of most chondrules in type ∼3.0 chondrites but comparable with those of Mg# < 98 chondrules in CR3 chondrites. Considered in conjunction with similar oxygen isotope ratios between Pyxie (and Iris) and Mg# < 98 chondrules in CR3 chondrites, it is inferred that the ferromagnesian Wild 2 particles and Mg# < 98 chondrules in CR3 chondrites formed late in local disk environments that had similar oxygen isotope ratios and redox states.
    No preview · Article · Dec 2014 · Earth and Planetary Science Letters
  • Amanda J White · Denton S Ebel
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    ABSTRACT: Light microscopy is a powerful tool that allows for many types of samples to be examined in a rapid, easy, and nondestructive manner. Subsequent image analysis, however, is compromised by distortion of signal by instrument optics. Deconvolution of images prior to analysis allows for the recovery of lost information by procedures that utilize either a theoretically or experimentally calculated point spread function (PSF). Using a laser scanning confocal microscope (LSCM), we have imaged whole impact tracks of comet particles captured in silica aerogel, a low density, porous SiO2 solid, by the NASA Stardust mission. In order to understand the dynamical interactions between the particles and the aerogel, precise grain location and track volume measurement are required. We report a method for measuring an experimental PSF suitable for three-dimensional deconvolution of imaged particles in aerogel. Using fluorescent beads manufactured into Stardust flight-grade aerogel, we have applied a deconvolution technique standard in the biological sciences to confocal images of whole Stardust tracks. The incorporation of an experimentally measured PSF allows for better quantitative measurements of the size and location of single grains in aerogel and more accurate measurements of track morphology.
    No preview · Article · Dec 2014 · Microscopy and Microanalysis
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    ABSTRACT: Magnetic fields are proposed to have played a critical role in some of the most enigmatic processes of planetary formation by mediating the rapid accretion of disk material onto the central star and the formation of the first solids. However, there have been no experimental constraints on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite were magnetized in a nebular field of 54 ± 21 microteslas. This intensity supports chondrule formation by nebular shocks or planetesimal collisions rather than by electric currents, the x-wind, or other mechanisms near the Sun. This implies that background magnetic fields in the terrestrial planet-forming region were likely 5 to 54 microteslas, which is sufficient to account for measured rates of mass and angular momentum transport in protoplanetary disks.
    Full-text · Article · Nov 2014 · Science
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    Alexander Hubbard · Denton S. Ebel
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    ABSTRACT: We consider the evidence presented by the LL3.0 chondrite Semarkona, including its chondrule fraction, chondrule size distribution and matrix thermal history. We show that no more than a modest fraction of the ambient matrix material in the Solar Nebula could have been melted into chondrules; and that much of the unprocessed matrix material must have been filtered out at some stage of Semarkona's parent body formation process. We conclude that agglomerations of many chondrules must have formed in the Solar Nebula, which implies that chondrules and matrix grains had quite different collisional sticking parameters. Further, we note that the absence of large melted objects in Semarkona means that chondrules must have exited the melting zone rapidly, before the chondrule agglomerations could form. The simplest explanation for this rapid exit is that chondrule melting occurred in surface layers of the disk. The newly formed, compact, chondrules then settled out of those layers on short time scales.
    Preview · Article · Sep 2014 · Icarus

  • No preview · Conference Paper · Sep 2014

  • No preview · Conference Paper · Sep 2014

  • No preview · Conference Paper · Sep 2014

Publication Stats

3k Citations
609.23 Total Impact Points


  • 2011-2016
    • Lamont - Doherty Earth Observatory Columbia University
      New York, New York, United States
  • 2014-2015
    • CUNY Graduate Center
      New York, New York, United States
  • 2002-2015
    • American Museum of Natural History
      • Division of Physical Sciences
      New York, New York, United States
  • 2012
    • Columbia University
      • Department of Earth and Environmental Sciences
      New York, New York, United States
  • 2010
    • Aix-Marseille Université
      Marsiglia, Provence-Alpes-Côte d'Azur, France
  • 2006
    • Muséum National d'Histoire Naturelle
      Lutetia Parisorum, Île-de-France, France
  • 2005
    • New Mexico Museum of Natural History and Science
      Albuquerque, New Mexico, United States
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
    • Planetary Science Institute
      American Fork, Utah, United States
  • 1997-2005
    • University of Chicago
      • Department of Geophysical Sciences
      Chicago, Illinois, United States
  • 1989-1994
    • Purdue University
      • Department of Earth and Atmospheric Sciences
      ウェストラファイエット, Indiana, United States