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ID 13957
JaLCDOI
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4
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Author
Nishiya, Nanayo
Kagami, Hiroo
Abstract
Rb-Sr isotopic study as well as petrologic investigations have been done on sixteen individul chondrule samples separated from the Allegan (H5) chondrite. The Rb-Sr chondrule isochron does not define a very precise age (4.42±0.17 Ga) and 87Sr/86Sr initial ratio (0.6997±0.0014) due to the very small variation in Rb/Sr ratio for the chondrules, whereas the model ages give a much more speciffic value (4.42±0.02 Ga). These ages may probably be indicative of the time of primary process (es) (e.g. chondrule formation) rather than secondary (metamorphic reheating) or tertiary (shock heating) processes in and/or on the H-chodrite parent body (or bodies). Chemical compositions of oliveines (Fa=17.5mol%, mean deviation (MD)=1.3%) and orthopyoxenes (Fs=15.4mol%, MD=3.2%) are moderately homogenized among the chondrules, while certains chemically uneguilibrated features are also distinctly preserved in this chondrite. Homogeneity of the mineral compositions, therefore, could not have been caused by thermal metamorphism but were probably inherited from processes prior to aggregation of the components. The overall implications of the chondrule isochron and model ages in relation to the petrological features and in comparison with Rb-Sr data of other chondrites of different chemical groups and petrologic types are discussed.
Keywords
chondrule
age
Rb-Sr isochron
Allegan
H- chondrite
meteorite
metamorphism
olivine
pyroxene
Publication Title
Okayama University Earth Science Report
Published Date
1994-09-20
Volume
volume1
Issue
issue1
Publisher
岡山大学理学部地球科学教室
Publisher Alternative
Department of Earth Sciences Faculty of Science, Okayama University
Start Page
27
End Page
36
ISSN
1340-7414
NCID
AN10506284
Content Type
Departmental Bulletin Paper
OAI-PMH Set
岡山大学
language
英語
Copyright Holders
岡山大学地球科学研究報告編集委員会
File Version
publisher
NAID
Eprints Journal Name
esr