The iron, magnesium, and calcium distribution in coexisting olivines and rhombic pyroxenes of chondrites

Keil, K.; Fredriksson, K.

doi:10.1029/jz069i016p03487

Cited by 296 publications

(112 citation statements)

References 59 publications

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“…They are subdivided into three groups (H, L, and LL) based on variations in bulk composition, such as molecular ratios [FeO/(FeO+MgO)] in olivine and pyroxene (Mason 1963;Keil & Fredriksson 1964) and the ratio of metallic Fe to total Fe (Dodd et al 1967). Their study, along with those of other chondrite classes, has provided numerous constraints on the formation and early evolution of the solar system, including (1) the migration processes that occurred in the protoplanetary disk prior to primary accretion (i.e., planetesimal formation) and their associated timescales (Cuzzi et al 2001;Cuzzi & Weidenschilling 2006), (2) the post-(and syn-) accretional heating events (Huss et al 2006;Ghosh et al 2006), and (3) the collisional events that occurred since their accretion (Hutchison 2004;Haack et al 1996, and references therein):…”

Section: Introductionmentioning

confidence: 99%

Multiple and Fast: The Accretion of Ordinary Chondrite Parent Bodies

Vernazza

Zanda

Binzel

et al. 2014

ApJ

125

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Although petrologic, chemical, and isotopic studies of ordinary chondrites and meteorites in general have largely helped establish a chronology of the earliest events of planetesimal formation and their evolution, there are several questions that cannot be resolved via laboratory measurements and/or experiments alone. Here, we propose the rationale for several new constraints on the formation and evolution of ordinary chondrite parent bodies (and, by extension, most planetesimals) from newly available spectral measurements and mineralogical analysis of main-belt S-type asteroids (83 objects) and unequilibrated ordinary chondrite meteorites (53 samples). Based on the latter, we suggest that spectral data may be used to distinguish whether an ordinary chondrite was formed near the surface or in the interior of its parent body. If these constraints are correct, the suggested implications include that: (1) large groups of compositionally similar asteroids are a natural outcome of planetesimal formation and, consequently, meteorites within a given class can originate from multiple parent bodies; (2) the surfaces of large (up to ∼200 km) S-type main-belt asteroids mostly expose the interiors of the primordial bodies, a likely consequence of impacts by small asteroids (D < 10 km) in the early solar system; (3) the duration of accretion of the H chondrite parent bodies was likely short (instantaneous or in less than ∼10 5 yr, but certainly not as long as 1 Myr); (4) LL-like bodies formed closer to the Sun than H-like bodies, a possible consequence of the radial mixing and size sorting of chondrules in the protoplanetary disk prior to accretion.

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Section: Introductionmentioning

confidence: 99%

Multiple and Fast: The Accretion of Ordinary Chondrite Parent Bodies

Vernazza

Zanda

Binzel

et al. 2014

ApJ

125

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“…Studying recent chondrites where both matrix and chromite-enclosed olivine and pyroxene are present, it is possible to determine whether compositional differences exist for extraterrestrial material as well. An analogue to the well established classification system for ordinary chondrites, founded on the fact that olivine and Ca-poor pyroxene in equilibrated (type 4-6) ordinary chondrites have specific ranges of chemical composition depending on group (H, L, LL; e.g., Mason, 1963;Keil and Fredriksson, 1964;Gomes and Keil, 1980;Rubin 1990), can then be established based on the inclusions. This would create an independent tool in the classification of fossil chondrites and sediment-dispersed extraterrestrial chromite grains originating from decomposed micrometeorites (Heck et al, 2008) and chondritic fragments related to impact events (Alwmark and Schmitz, 2007), when no matrix silicates are preserved or present.…”

Section: Introductionmentioning

confidence: 99%

Relict silicate inclusions in extraterrestrial chromite and their use in the classification of fossil chondritic material

Alwmark

Schmitz

2009

Geochimica et Cosmochimica Acta

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Chromite is the only common meteoritic mineral surviving long-term exposure on Earth, however, the present study of relict chromite from numerous Ordovician (470 Ma) fossil meteorites and micrometeorites from Sweden, reveals that when encapsulated in chromite, other minerals can survive for hundreds of millions of years maintaining their primary composition. The most common minerals identified, in the form of small (<1-10 lm) anhedral inclusions, are olivine and pyroxene. In addition, sporadic merrillite and plagioclase were found.Analyses of recent meteorites, holding both inclusions in chromite and corresponding matrix minerals, show that for olivine and pyroxene inclusions, sub-solidus re-equilibration between inclusion and host chromite during entrapment has led to an increase in chromium in the former. In the case of olivine, the re-equilibration has also affected the fayalite (Fa) content, lowering it with an average of 14% in inclusions. For Ca-poor pyroxene the ferrosilite (Fs) content is more or less identical in inclusions and matrix. By these studies an analogue to the commonly applied classification system for ordinary chondritic matrix, based on Fa in olivine and Fs in Ca-poor pyroxene, can be established also for inclusions in chromite. All olivine and Ca-poor pyroxene inclusions (>1.5 lm) in chromite from the Ordovician fossil chondritic material plot within the Lchondrite field, which is in accordance with previous classifications. The concordance in classification together with the fact that inclusions are relatively common makes them an accurate and useful tool in the classification of extraterrestrial material that lacks matrix silicates, such as fossil meteorites and sediment-dispersed chromite grains originating primarily from decomposed micrometeorites but also from larger impacts.

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“…The sample was subsequently stored in tightly closed bottles. The sample is representative of olivine-hypersthene meteorites (Keil and Fredriksson, 1964), and, more specifically, it is representative of class L6 (Tandonand Wasson, 1968). The black fusion crust was chipped off, and the remaining meteorite was fractured in a rock crusher to produce a minimum of small particles.…”

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confidence: 99%

Photometric and polarimetric properties of the bruderheim chondritic meteorite

Egan¹,

Veverka

Noland

et al. 1973

Icarus

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RE -447T.fABSTRACT r Photometric and polarimetric laboratory measurements were made, as a function of phase angle in the U(0.36 im), G(0.541.m) and R(0.67Lm) bands for 0 , 30O and 600 incident illumination on four particle size ranges of Bruderheim, an L6 olivine-hypersthene chondritic meteorite.The four particle size ranges were: 0.25-4.76mm, 0.25-4.76mm coated with <74lm powder, 74-250pm, and < 37pm. In addition, normal reflectance measurments were made in the spectral range from 0.31 to 1.1lm. Comparison with astronomical data reveals that none of the asteroids in the main belt for which adequate observations exist can be matched with Bruderheim, which is representative of the most common meteoritic material encountered by the Earth. However, it appears from the polarization and photometry data that the surface of-the Apollo asteroid Icarus is consistent with an ordinary chondrite composition. ' This suggests the possibility that this material, although common in Earth-crossing orbits, is rare as a surface constituent in the main asteroid belt.ii . I INTRODUCTIONRecently, much astronomical effort has been devoted to the study of the physical properties of asteroid surfaces. This has resulted in an ever growing store of spectral, photometric, and polarimetric data that 'have not been sufficiently complemented by laboratory measurements.Because there are many indirect arguments (Anders, 1964) which indicate that most meteorites are fragments of asteroid bodies, and since McCord, et al. (1970) 'have successfully identified the spectral reflectance curve of one asteroid, Vesta, with that of a basaltic achondrite, laboratory measurments on meteorite samples should prove useful in an intrepretation of asteroid surfaces. We 'have chosen to study the spectral, photometric, and polarimetric properties of the Bruderheim olivine-hypersthene chondrite, which is representative of the most common meteoritic material recovered on Earth (Mason, 1962), and, hence, might also be the most common in interplanetary space. II INSTRUMENTATIONThe Grumman goniometer, designed to measure the polarimetric and photometric properties of samples up to 60mm in diameter, consists of a light source on a 3-meter long arm and a sensor on another 3-meter long arm. The center of rotation of the arms is situated on the average sample surface, and the average normal to the surface lies in the plane defined by the arms.The source is a G-E Type 2331 tungsten lamp, followed by a quartz ground glass diffuser, a Lyot depolarizer, an aperture plate, a 420 cycle, seven 1' bladed chopper, and an 11.4 cm diameter quartz objective lens. This assembly produces a beam collimated to 1°, of uniform brightness to 1 percent or less, with a residual polarization of 0.1 percent or less on the 60mm illuminated sample area. The source arm is ordinarily fixed at an incident illumination angle between 0 and 60 degrees.The sensors used in this investigation were photomultipliers RCA Types 6199 and 7102 with mumetal shields. The sensor arm normally traverses a phase ang...

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The iron, magnesium, and calcium distribution in coexisting olivines and rhombic pyroxenes of chondrites

Cited by 296 publications

References 59 publications

Multiple and Fast: The Accretion of Ordinary Chondrite Parent Bodies

Multiple and Fast: The Accretion of Ordinary Chondrite Parent Bodies

Relict silicate inclusions in extraterrestrial chromite and their use in the classification of fossil chondritic material

Photometric and polarimetric properties of the bruderheim chondritic meteorite

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