Chemical and physical studies of chondrites: X. Cathodoluminescence and phase composition studies of metamorphism and nebular processes in chondrules of type 3 ordinary chondrites

Dehart, J. M.; Lofgren, G. E.; Lü, Junfu; Benoit, P. H.; Sears, D. W. G.

doi:10.1016/0016-7037(92)90171-e

Cited by 48 publications

(34 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1 la,b). Moreover, the CL characteristics of the chondrules in enstatite chondrites differ from those of chondrules in ordinary chondrites (Sears et al, 1992). Thus the compositional classification scheme for chondrules in ordinary chondrites cannot be applied directly in its current form to the chondrules in enstatite chondrites.…”

Section: Classification Of Enstatite Chondrite Chondrulesmentioning

confidence: 98%

“…Later classification schemes focused on mineral composition and bulk composition, such as the separation into type I (with FeO-poor olivines) and type I1 (with FeO-rich olivines) chondrules (McSween, 1977a), subdivided by calcium abundance in olivine (Scott and Taylor, 1983;Jones 1990Jones , 1994. Another classification system for ordinary and carbonaceous chondrules focused on olivine and mesostasis composition (Sears et al, 1992;DeHart et al, 1992;Huang et al, 1996). The placement of chondrules from enstatite chondrites in these systems has not been extensively explored.…”

Section: Introductionmentioning

confidence: 99%

“…The chondrules in ordinary and carbonaceous chondrites have been well studied, and textures, bulk compositions, and mineral compositions have been used to classify chondrules as an aid to interpreting their formational histories (e.g., McSween, 1977a,b;King, 1978, 1979;Dodd, 1981;Gooding and Keil, 1981;Scott and Taylor, 1983;Rubin and Keil, 1984;Rubin, 1989;Sears et al, 1992;Jones, 1994;Huang et al, 1996). Dodd (1981) argued that while chondrules in ordinary chondrites were mainly "lithic", or porphorytic, types, chondrules in carbonaceous chondrites were predominantly "droplet", or glass-rich or fine-grained, types, and that the different classes had fundamentally different histories.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Properties of chondrules in EL3 chondrites, comparison with EH3 chondrites, and the implications for the formation of enstatite chondrites

Schneider

Symes

Benoit

et al. 2002

Meteorit & Planetary Scien

View full text Add to dashboard Cite

Abstract-The study of chondrules provides information about processes occurring in the early solar system. In order to ascertain to what extent these processes played a role in determining the properties of the enstatite chondrites, the physical and chemical properties of chondrules from three EL3 chondrites and three EH3 chondrites have been examined by optical, cathodoluminescence (CL), and electron microprobe techniques. Properties examined include size, texture, CL, and composition of both individual phases and bulk chondrules. The textures, distribution of textures, and composition of silicates of the EL3 chondrules resemble those of EH3 chondrules. However, the chondrules from the two classes differ in that (1) the size distribution of the EL chondrules is skewed to larger values than EH chondrules, (2) the enstatite in EL chondrules displays varying shades of red CL due to the presence of fine-grained sulfides and metal in the silicates, and (3) the mesostasis of EH chondrules is enriched in Na relative to that of EL chondrules. The similarities between the chondrules of the two classes suggest similar precursor materials, while the differences suggest that there was not a single reservoir of meteoritic chondrules, but that their origin was fairly local. The differences in the size distribution of chondrules in EH and EL chondrites may be explained by aerodynamic and gravitational sorting during accumulation of the meteoric material, while differences in CL and mesostasis properties may reflect differences in formation conditions and cooling rate following chondrule formation. We argue that our observations are consistent with the formation of enstatite chondrites in a thick dynamic regolith on their parent body.

show abstract

Section: Classification Of Enstatite Chondrite Chondrulesmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Properties of chondrules in EL3 chondrites, comparison with EH3 chondrites, and the implications for the formation of enstatite chondrites

Schneider

Symes

Benoit

et al. 2002

Meteorit & Planetary Scien

View full text Add to dashboard Cite

show abstract

“…However, the volatile element content of Krymka is quite low, comparable with middle type 3 ordinary chondrites (Anders and Zadnik 1985). Many of the studies that have been helpful in distinguishing type 3.0 from 3.1 chondrites (e.g., DeHart et al 1992;Sears et al 1990) have not included any type 3.2 chondrites for comparison, mainly because few of them are known. On the basis of the low TL sensitivity of these meteorites, but also the low Cr 2 O 3 in olivine and other properties indicating mild metamorphism (see below), Krymka and GRO 95502/95544 are placed in the type 3.2 category.…”

Section: Lit Fes Wt%mentioning

confidence: 99%

“…DeHart et al (1992) found that there are differences in the proportions of various types of chondrules among these low petrologic type chondrites. FeO-poor chondrules displaying yellow cathodoluminescence (CL) in their mesostasis are most abundant in type 3.0 chondrites.…”

Section: Introductionmentioning

confidence: 99%

The onset of metamorphism in ordinary and carbonaceous chondrites

Grossman

Brearley

2005

Meteorit & Planetary Scien

342

441

View full text Add to dashboard Cite

Received May 18, 2004; revision accepted November 3, 2004) Abstract-Ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by Xray mapping techniques. A variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and cathodoluminescence (CL) methods. The matrix in the least metamorphosed chondrites is rich in S and Na. The S is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains. Progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules. Alkalis initially leave the matrix and enter chondrules during early metamorphism. Feldspar subsequently nucleates in the matrix and Na re-enters from chondrules. These metamorphic trends can be used to refine classification schemes for chondrites. Cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to subdivide types 3.0 and 3.1 into types 3.00 through 3.15. On this basis, the most primitive ordinary chondrite known is Semarkona, although even this meteorite has experienced a small amount of metamorphism. Allan Hills (ALH) A77307 is the least metamorphosed CO chondrite and shares many properties with the ungrouped carbonaceous chondrite Acfer 094. Analytical problems are significant for glasses in type II chondrules, as Na is easily lost during microprobe analysis. As a result, existing schemes for chondrule classification that are based on the alkali content of glasses need to be revised.

show abstract

Chondrule formation, metamorphism, brecciation, an important new primary chondrule group, and the classification of chondrules

Sears

Shaoxiong

Benoit

1995

Earth and Planetary Science Letters

Self Cite

View full text Add to dashboard Cite

The recently proposed compositional classification scheme for meteoritic chondrules divides the chondrules into groups depending on the composition of their two major phases, olivine (or pyroxene) and the mesostasis, both of which are genetically important. The scheme is here applied to discussions of three topics: the petrographic classification of Roosevelt County 075 (the least-metamorphosed H chondrite known), brecciation (an extremely important and ubiquitous process probably experienced by > 40% of all unequilibrated ordinary chondrites), and the group A5 chondrules in the least metamorphosed ordinary chondrites which have many similarities to chondrules in the highly metamorphosed 'equilibrated' chondrites.Since composition provides insights into both primary formation properties of the chondrules and the effects of metamorphism on the entire assemblage it is possible to determine the petrographic type of RC075 as 3.1 with unique certainty. Similarly, the new scheme can be applied to individual chondrules without knowledge of the petrographic type of the host chondrite, which makes it especially suitable for studying breccias. Finally, the new scheme has revealed the existence of chondrules not identified by previous techniques and which appear to be extremely important. Like group AI and A2 chondrules (but unlike group B1 chondrules) the primitive group A.5 chondrules did not supercool during formation, but unlike group AI and A2 chondrules (and like group B1 chondrules) they did not suffer volatile loss and reduction during formation. It is concluded that the compositional classification scheme provides important new insights into the formation and history of chondrules and chondrites which would be overlooked by previous schemes.

show abstract

Chemical and physical studies of chondrites: X. Cathodoluminescence and phase composition studies of metamorphism and nebular processes in chondrules of type 3 ordinary chondrites

Cited by 48 publications

References 36 publications

Properties of chondrules in EL3 chondrites, comparison with EH3 chondrites, and the implications for the formation of enstatite chondrites

Properties of chondrules in EL3 chondrites, comparison with EH3 chondrites, and the implications for the formation of enstatite chondrites

The onset of metamorphism in ordinary and carbonaceous chondrites

Chondrule formation, metamorphism, brecciation, an important new primary chondrule group, and the classification of chondrules

Contact Info

Product

Resources

About