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Record 67 of 1291
The classification and complex thermal history of the enstatite chondrites
External Online Source: doi:10.1029/95JE00502
Author and Affiliation:
Zhang, Yanhong(Unviersity of Arkansas, Fayetteville, AR, United States)
Benoit, Paul H.(Unviersity of Arkansas, Fayetteville, AR, United States)
Sears, Derek W. G.(Unviersity of Arkansas, Fayetteville, AR, United States)
Abstract: We have carried out instrumental neutron activation analysis of 11 enstatite chondrites and electron microprobe analyses of 17 enstatite chondrites, most of which were previously little described. We report here the third known EH5 chondrite (LEW 88180) and an unusual EL6 chondrite (LEW 87119), new data on four EL3 chondrites (ALH 85119, EET 90299, PCA 91020, and MAC 88136, which is paired with MAC 88180 and MAC 88184), the second EL5 chondrite (TIL 91714), and an unusual metal-rich and sulfide-poor EL3 chondrite (LEW 87223). The often discussed differences in mineral composition displayed by the EH and EL chondrites are not as marked after the inclusion of the new samples in the database, and the two classes apparently experienced a similar range of equilibrium temperatures. However, texturally the EL chondrites appear to have experienced much higher levels of metamorphic alteration than EH chondrites of similar equilibration temperatures. Most of the petrologic type criteria are not applicable to enstatite chondrites and, unlike the ordinary chondrites, texture and mineralogy reflect different aspects of the meteorite history. We therefore propose that the existing petrologic type scheme not be used for enstatite chondrites. We suggest that while 'textural type' reflects peak metamorphic temperatures, the 'mineralogical type' reflects equilibration during postmetamorphic (probably regolith) processes. Unlike the ordinary chondrites and EH chondrites, EL chondrites experienced an extensive low-temperature metamorphic episode. There are now a large number of enstatite meteorite breccias and impact melts, and apparently surface processes were important in determining the present nature of the enstatite chondrites.
Publication Date: May 25, 1995
Document ID:
19950059126
(Acquired Dec 28, 1995)
Accession Number: 95A90725
Subject Category: LUNAR AND PLANETARY EXPLORATION
Document Type: Journal Article
Publication Information: Journal of Geophysical Research (ISSN 0148-0227); 100; E5; p. 9417-9438
Publisher Information: United States
Contract/Grant/Task Num: NAGW-3519
Financial Sponsor: NASA; United States
Organization Source: NASA; Washington, DC, United States
Description: 22p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
NASA Terms: CHONDRITES; CLASSIFICATIONS; GEOCHRONOLOGY; NEUTRON ACTIVATION ANALYSIS; PETROLOGY; SPECTROSCOPIC ANALYSIS; TEMPERATURE EFFECTS; CHEMICAL COMPOSITION; MINERALOGY; TEMPERATURE MEASUREMENT; TEXTURES
Imprint And Other Notes: Journal of Geophysical Research vol. 100, no. E5 p. 9417-9438 May 25, 1995
Availability Source: Other Sources
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