Bleached chondrules: Evidence for widespread aqueous processes on the parent asteroids of ordinary chondrites

Grossman, J. N.; Alexander, Conel M. O'd.; Wang, Jingyuan; Brearley, Adrian J.

doi:10.1111/j.1945-5100.2000.tb01429.x

Cited by 162 publications

(166 citation statements)

References 38 publications

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“…The chondrules in the Smithsonian thin sections that were analyzed by EPMA and ion probe methods were not available for TEM work. As described by Grossman et al (2000), demountable, doubly polished petrographic thin sections were prepared from eight small chips ofSemarkona (USNM 1805). One ofthese contained the bleached chondrule analyzed in the earlier study.…”

Section: Transmission Electron Microscopymentioning

confidence: 99%

Zoned chondrules in Semarkona: Evidence for high‐ and low‐temperature processing

Grossman

Alexander

Wang

et al. 2002

Meteorit & Planetary Scien

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Abstract-At least 15% of the 10w-FeO chondrules in Semarkona (LL3.0) have mesostases that are concentrically zoned in Na, with enrichments near the outer margins. We have studied zoned chondrules using electron microprobe methods (x-ray mapping plus quantitative analysis), ion microprobe analysis for trace elements and hydrogen isotopes, cathodoluminescence imaging, and transmission electron microscopy in order to determine what these objects can tell us about the environment in which chondrules formed and evolved.Mesostases in these chondrules are strongly zoned in all moderately volatile elements and H (interpreted as water). Calcium is depleted in areas ofvolatile enrichment. Titanium and Cr generally decrease toward the chondrule surfaces, whereas Al and Si may either increase or decrease, generally in opposite directions to one another; Mn follows Na in some chondru1es but not in others; Fe and Mg are unzoned. D/H ratios increase in the water-rich areas of zoned chondrules. Mesostasis shows cathodoluminescence zoning in most zoned chondrules, with the brightest yellow color near the outside. Mesostasis in zoned chondrules appears to be glassy, with no evidence for devitrification.Systematic variations in zoning patterns among pyroxene-and olivine-rich chondrules may indicate that fractionation oflow-and high-Ca pyroxene played some role in Ti, Cr, Mn, Si, AI, and some Ca zoning. But direct condensation ofelements into hot chondrules, secondary melting oflate condensates into the outer portions of chondrules, and subsolidus diffusion of elements into warm chondrules cannot account for the sub-parallel zoning profiles ofmany elements, the presence ofH20, or elemental abundance patterns.Zoning ofmoderately volatile elements and Ca may have been produced by hydration of chondrule glass without devitrification during aqueous alteration on the parent asteroid. This could have induced structural changes in the glass allowing rapid diffusion and exchange of elements between altered glass and surrounding matrix and rim material. Calcium was mainly lost during this process, and other nonvolatile elements may have been mobile as well. Some unzoned, 10w-FeO chondrules appear to have fully altered mesostasis.

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Section: Transmission Electron Microscopymentioning

confidence: 99%

Zoned chondrules in Semarkona: Evidence for high‐ and low‐temperature processing

Grossman

Alexander

Wang

et al. 2002

Meteorit & Planetary Scien

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“…Unlike the Themis family, however, the Koronis family is dominated by S-type asteroids (Bell 1989;Binzel et al 1993;Mothé-Diniz et al 2005), which along with their meteoritic analogs, the ordinary chondrites, do not exhibit evidence of significant aqueous alteration (e.g., Rivkin et al 2002). Nonetheless, due to the high collision rates within this family and the possibility that these asteroids may not be completely anhydrous (Grossman et al 2000;Keil 2000), Koronis family asteroids were still judged to be viable 133P-analog candidates. Koronis family targets were selected by a hierarchical clustering analysis, using a cutoff value of δv = 50 m s −1 with respect to (158) Koronis.…”

Section: Survey Designmentioning

confidence: 99%

The Hawaii trails project: comet-hunting in the main asteroid belt

Hsieh

2009

A&A

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Context. The mysterious solar system object 133P/(7968) Elst-Pizarro is dynamically asteroidal, yet displays recurrent comet-like dust emission. Two scenarios were hypothesized to explain this unusual behavior: 1) 133P is a classical comet from the outer solar system that has evolved onto a main-belt orbit or 2) 133P is a dynamically ordinary main-belt asteroid on which subsurface ice has recently been exposed. If 1) is correct, the expected rarity of a dynamical transition onto an asteroidal orbit implies that 133P could be alone in the main belt. In contrast, if 2) is correct, other icy main-belt objects should exist and could also exhibit cometary activity. Aims. Believing 133P to be a dynamically ordinary, yet icy main-belt asteroid, I set out to test the primary prediction of the hypothesis: that 133P-like objects should be common and could be found by an appropriately designed observational survey. Methods. I conducted just such a survey -the Hawaii Trails Project -of selected main-belt asteroids in a search for objects displaying cometary activity. Optical observations were made of targets selected from among the Themis, Koronis, and Veritas asteroid families, the Karin asteroid cluster, and low-inclination, kilometer-scale outer-belt asteroids, using the Lulin 1.0 m, small and moderate aperture research telescope system (SMARTS) 1.0 m, University of Hawaii 2.2 m, southern astrophysical research (SOAR) 4.1 m, Gemini North 8.1 m, Subaru 8.2 m, and Keck I 10 m telescopes. Results. I made 657 observations of 599 asteroids, discovering one active object now known as 176P/LINEAR, leading to the identification of the new cometary class of main-belt comets (MBCs). These results suggest that there could be ∼100 currently active MBCs among low-inclination, kilometer-scale outer-belt asteroids. Physically and statistically, MBC activity is consistent with initiation by meter-sized impactors. The estimated rate of impacts and sizes of resulting active sites, however, imply that 133P-sized bodies should become significantly devolatilized over Gyr timescales, suggesting that 133P, and possibly the other MBCs as well, could be secondary, or even multigenerational, fragments from recent breakup events.

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“…Observations on only two CC chondrules (Grossman et al 2000) were used to give the average observed composition in Table 2. Because of this, the uncertainties are relatively large.…”

Section: Detailed Calculationsmentioning

confidence: 99%

“…Nebular gas composition (molar) (Anders and Grevesse 1989 1994, 1996a, 1996bGrossman et al 2000). Type IA chondrules contain only or mainly low-FeO olivine as the crystal phase.…”

Section: Calculations Of Average Chondrule Compositionsmentioning

confidence: 99%

Non‐equilibrium concepts lead to a unified explanation of the formation of chondrules and chondrites

Blander¹,

Pelton²,

Jung³

et al. 2004

Meteorit & Planetary Scien

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Non-equilibrium concepts lead to a unified explanation of the formation of chondrules and chondritesAbstract-Calculations of the formation of seven types of chondrules in Semarkona from a gas of solar composition were performed with the FACT computer program to predict the chemistries of oxides (including silicates), developed by the authors and their colleagues. The constrained equilibrium theory was used in the calculations with two nucleation constraints suggested by nucleation theory. The first constraint was the blocking of Fe and other metal gaseous atoms from condensing to form solids or liquids because of very high surface free energies and high surface tensions of the solid and liquid metals, respectively. The second constraint was the blocking of the condensation of solids and the formation of metastable liquid oxides (including silicates) well below their liquidus temperatures. Our laboratory experiments suggested subcooling of type IIA chondrule compositions of 400 degrees or more below the liquidus temperature. The blocking of iron leads to a supersaturation of Fe atoms, so that the partial pressure of Fe (p Fe ) is larger than the partial pressure at equilibrium (p Fe (eq)). The supersaturation ratio S = p Fe /p Fe (eq) becomes larger than 1 and increases rapidly with a decrease in temperature. This drives the reaction Fe + H 2 O ⇔ H 2 + FeO to the right. With S = 100, the activity of FeO in the liquid droplet is 100 times as large as the value at equilibrium. The FeO activities are a function of temperature and provide relative average temperatures of the crystallization of chondrules. Our calculations for the LL3.0 chondrite Semarkona and our study of some non-equilibrium effects lead to accurate representations of the compositions of chondrules of types IA, IAB, IB, IIA, IIAB, IIB, and CC. Our concepts readily explain both the variety of FeO concentrations in the different chondrule types and the entire process of chondrule formation. Our theory is unified and could possibly explain the formation of chondrules in all chondritic meteorites as well as provide a simple explanation for the complex chemistries of chondrites, and especially for type 3 chondrites.

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Bleached chondrules: Evidence for widespread aqueous processes on the parent asteroids of ordinary chondrites

Cited by 162 publications

References 38 publications

Zoned chondrules in Semarkona: Evidence for high‐ and low‐temperature processing

Zoned chondrules in Semarkona: Evidence for high‐ and low‐temperature processing

The Hawaii trails project: comet-hunting in the main asteroid belt

Non‐equilibrium concepts lead to a unified explanation of the formation of chondrules and chondrites

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