Evidence for relict grains in chondrules of Qingzhen, an E3 type enstatite chondrite

Rambaldi, E. R.; Rajan, R. S.; Wang, D.; Housley, R. M.

doi:10.1016/0012-821x(83)90122-x

Cited by 44 publications

(34 citation statements)

References 17 publications

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“…The heating duration was probably "short" for chondrules (Hewins, 1989(Hewins, , 1997 and for CLSs. Crystal-bearing lunar spherules show no evidence for FeO reduction during heating, contrary to the situation for some chondrules (e.g., Huang et al, 1996;Sears et al, 1 9 9 6~;Rambaldi, 1981;Rambaldi et al, 1983). This may indicate that chondrules were exposed to one or more reducing agents (H2 gas?…”

Section: Propertiescontrasting

confidence: 41%

Crystal‐bearing lunar spherules: Impact melting of the Moon's crust and implications for the origin of meteoritic chondrules

Ruzicka

Snyder

Taylor

2000

Meteorit & Planetary Scien

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Abstract-Crystal-bearing lunar spherules (CLSs) in lunar breccia (143 13, 143 15, 143 18), soil (68001, 241 OS), and impact-melt rock (62295) samples can be classified into two types: feldspathic and olivine-rich. Feldspathic CLSs contain equant, tabular, or acicular plagioclase grains set in glass or a pyroxene-olivine mesostasis; the less common olivine-rich CLSs contain euhedral or skeletal olivine set in glass, or possess a barred-olivine texture. Bulk-chemical and mineral-chemical data strongly suggest that feldspathic CLSs formed by impact melting of mixtures of ferroan anorthosite and Mg-suite rocks that compose the feldspathic crust of the Moon. It is probable that olivine-rich CLSs also formed by impact melting, but some appear to have been derived from distinctively magnesian lunar materials, atypical of the Moon's crust.Some CLSs contain reversely-zoned "relic" plagioclase grains that were not entirely melted during CLS formation, thin (25 p m thick) rims of troilite or phosphate, and chemical gradients in glassy mesostases attributed to metasomatism in a volatile-rich (Na-K-P-rich) environment. Crystal-bearing lunar spherules were rimmed and metasomatized prior to brecciation. Compound CLS objects are also present; these formed by lowvelocity collisions in an environment, probably an ejecta plume, that contained numerous melt droplets.Factors other than composition were responsible for producing the crystallinity of the CLSs. We agree with previous workers that relatively slow cooling rates and long ballistic travel times were critical features that enabled these impact-melt droplets to partially or completely crystallize in free-flight. Moreover, incomplete melting of precursor materials formed nucleation sites that aided subsequent crystallization.Clearly, CLSs do not resemble meteoritic chondrules in all ways. The two types of objects had different precursors and did not experience identical rimming processes, and vapor fractionation appears to have played a less important role in establishing the compositions of CLSs than of chondrules. However, the many detailed similarities between CLSs and chondrules indicate that it is more difficult to rule out an origin for some chondrules by impact melting than some have previously argued. Differences between CLSs, chondrules, and their host rocks possibly can be reconciled with an impact-melt origin for some chondrules when different precursors, the higher gravity of the Moon compared to chondrite parent bodies, and the likely presence of nebular gas during chondrule formation are taken into account.

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Section: Propertiescontrasting

confidence: 41%

Crystal‐bearing lunar spherules: Impact melting of the Moon's crust and implications for the origin of meteoritic chondrules

Ruzicka

Snyder

Taylor

2000

Meteorit & Planetary Scien

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“…1d). Rambaldi et al (1983) showed that some metal in pyroxene in EH chondrules contains low amounts of Si and Ni. Such fine-grained Ni-free Fe-metal is also found in FeOrich pyroxenes in Sahara 97159 (Fig.…”

Section: Fe-ni Metalsmentioning

confidence: 99%

FeO‐rich silicates in the Sahara 97159 (EH3) enstatite chondrite: Mineralogy, oxygen isotopic compositions, and origin

Kimura

Hiyagon

Lin

et al. 2003

Meteorit & Planetary Scien

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“…The tiny metal blebs within olivines are poorer in Ni than the more abundant spherical metal grains present in chondrule interiors (Rambaldi and Wasson 1981). The occurrences of both metallic blebs and FeO depletion in olivine have been interpreted as the result of a solid state reduction of more ferroan olivines (Boland and Duba 1981;Rambaldi 1981;Nagahara 1981;Rambaldi and Wasson 1982;Rambaldi et al 1983;Connolly et al, 1994;Libourel and Chaussidon 1995;Jones 1996;Jones and Danielson 1997). Recently, Lemelle et al (2000) confirmed this idea and proposed that the formation of dusty olivines could be explained by a coupled reduction/volatilization reaction.…”

Section: Introductionmentioning

confidence: 99%

“…In addition to spheroidal Fe-Ni metal grains, magnesian chondrules (Type I) in unequilibrated chondrites frequently contain FeO-poor olivine grains riddled with µm-sized Fe metal blebs (Rambaldi, Sears, and Wasson 1980;Rambaldi 1981;Nagahara 1981;Rambaldi and Wasson 1982;Rambaldi et al 1983;Kracher, Scott, and Keil 1984;Jones 1996). These metallic inclusions are located in the cores of coarse olivine grains of forsteritic composition, giving a characteristic "dusty" appearance to the olivines (Fig.…”

Section: Introductionmentioning

confidence: 99%

Experimental study and TEM characterization of dusty olivines in chondrites: Evidence for formation by in situ reduction

Leroux¹,

Libourel²,

Lemelle³

et al. 2003

Meteorit & Planetary Scien

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Abstract-An analytical transmission electron microscopy (ATEM) study was undertaken in order to better understand the formation conditions of dusty olivines (i.e., olivines containing abundant tiny inclusions of Fe-Ni metal) in primitive meteorites. Dusty olivines from type I chondrules in the Bishunpur chondrite (LL3.1) and from synthetic samples obtained by reduction of San Carlos olivines were examined. In both natural and experimental samples, micron size metal blebs observed in the dusty region often show preferential alignments along crystallographic directions of the olivine grains, have low Ni contents (typically <2 wt%), and are frequently surrounded by a silica-rich glass layer. These features suggest that dusty olivines are formed by a sub-solidus reduction of initially fayalitic olivines according to the following reaction:Fe 2 SiO 4 in olivine = 2Fe metal + xSiO 2 in melt + (1−x) SiO in gas + (3−x)/2O 2 in gas Some volatilization of SiO gas may account for the apparent excess of metal relative to silica-rich glass observed in both experimental and natural samples. Comparison with experimentally produced dusty olivines suggests that time scales of the order of minutes usually inferred for chondrule formation are also adequate for the formation of dusty olivines. These observations are in agreement with the hypothesis that at least part of the metal phase in chondrites originated from reduction during chondrule formation.

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Evidence for relict grains in chondrules of Qingzhen, an E3 type enstatite chondrite

Cited by 44 publications

References 17 publications

Crystal‐bearing lunar spherules: Impact melting of the Moon's crust and implications for the origin of meteoritic chondrules

Crystal‐bearing lunar spherules: Impact melting of the Moon's crust and implications for the origin of meteoritic chondrules

FeO‐rich silicates in the Sahara 97159 (EH3) enstatite chondrite: Mineralogy, oxygen isotopic compositions, and origin

Experimental study and TEM characterization of dusty olivines in chondrites: Evidence for formation by in situ reduction

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