Thermal history of the shock-melted Antarctic LL-chondrites from the Yamato-79 collection

Osamu Okano, Noboru Nakamura, Keisuke Nagao

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

The Sr and rare gas isotopic compositions and abundances of lithophile trace elements (K, Rb, Sr, Ba, and REEs) were determined for a series of shock-melted Yamato-79 LL-chondrites to investigate their late thermal history and the chemical features of shock processes. All meteorites show similarities in shock ages (~ 1.2 Ga) as confirmed by Rb-Sr internal isochron and K-Ar dating, rare gas compositions as well as cosmic-ray exposure ages (~28 Ma), petrographie textures, and sampling sites in Antarctica. These results indicate that all of these meteorites are part of the same fall. The 1.2 Ga shock event caused a severe (partial to total) melting followed by recrystallization of olivine and clinopyroxene, vesiculation, shock-induced alkali homogenization, and local isotopic equilibration or perturbation of the Rb-Sr system. The degrees of shock effects are variable from specimen to specimen and from portion to portion, even in a single specimen. Model calculations of Fe diffusion in olivine suggest that hot and cold materials were in close contact in the impact ejecta sheets of the parent body. From these model calculations and the evidence provided by cosmogenic rare gas compositions, it is concluded that an impact melt ejecta pile composed of hot and cold brecciated materials had formed at depth (> 2 m, shielded from cosmic rays) in an impact crater by the 1.2 Ga event. The parent body was fragmented to meter-size stones by an additional collision at ~28 Ma resulting in the formation of the parent material of the Yamato-79 shocked chondrites.

Original languageEnglish
Pages (from-to)3509-3523
Number of pages15
JournalGeochimica et Cosmochimica Acta
Volume54
Issue number12
DOIs
Publication statusPublished - 1990
Externally publishedYes

Fingerprint

Noble Gases
chondrite
Meteorites
Cosmic rays
parent body
ejecta
meteorite
cosmic ray
olivine
history
Chemical analysis
gas
Trace Elements
Alkalies
parent material
clinopyroxene
Piles
crater
Melting
pile

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Thermal history of the shock-melted Antarctic LL-chondrites from the Yamato-79 collection. / Okano, Osamu; Nakamura, Noboru; Nagao, Keisuke.

In: Geochimica et Cosmochimica Acta, Vol. 54, No. 12, 1990, p. 3509-3523.

Research output: Contribution to journalArticle

Okano, Osamu ; Nakamura, Noboru ; Nagao, Keisuke. / Thermal history of the shock-melted Antarctic LL-chondrites from the Yamato-79 collection. In: Geochimica et Cosmochimica Acta. 1990 ; Vol. 54, No. 12. pp. 3509-3523.
@article{149655646a964966a7ecd91309d41db7,
title = "Thermal history of the shock-melted Antarctic LL-chondrites from the Yamato-79 collection",
abstract = "The Sr and rare gas isotopic compositions and abundances of lithophile trace elements (K, Rb, Sr, Ba, and REEs) were determined for a series of shock-melted Yamato-79 LL-chondrites to investigate their late thermal history and the chemical features of shock processes. All meteorites show similarities in shock ages (~ 1.2 Ga) as confirmed by Rb-Sr internal isochron and K-Ar dating, rare gas compositions as well as cosmic-ray exposure ages (~28 Ma), petrographie textures, and sampling sites in Antarctica. These results indicate that all of these meteorites are part of the same fall. The 1.2 Ga shock event caused a severe (partial to total) melting followed by recrystallization of olivine and clinopyroxene, vesiculation, shock-induced alkali homogenization, and local isotopic equilibration or perturbation of the Rb-Sr system. The degrees of shock effects are variable from specimen to specimen and from portion to portion, even in a single specimen. Model calculations of Fe diffusion in olivine suggest that hot and cold materials were in close contact in the impact ejecta sheets of the parent body. From these model calculations and the evidence provided by cosmogenic rare gas compositions, it is concluded that an impact melt ejecta pile composed of hot and cold brecciated materials had formed at depth (> 2 m, shielded from cosmic rays) in an impact crater by the 1.2 Ga event. The parent body was fragmented to meter-size stones by an additional collision at ~28 Ma resulting in the formation of the parent material of the Yamato-79 shocked chondrites.",
author = "Osamu Okano and Noboru Nakamura and Keisuke Nagao",
year = "1990",
doi = "10.1016/0016-7037(90)90301-Z",
language = "English",
volume = "54",
pages = "3509--3523",
journal = "Geochmica et Cosmochimica Acta",
issn = "0016-7037",
publisher = "Elsevier Limited",
number = "12",

}

TY - JOUR

T1 - Thermal history of the shock-melted Antarctic LL-chondrites from the Yamato-79 collection

AU - Okano, Osamu

AU - Nakamura, Noboru

AU - Nagao, Keisuke

PY - 1990

Y1 - 1990

N2 - The Sr and rare gas isotopic compositions and abundances of lithophile trace elements (K, Rb, Sr, Ba, and REEs) were determined for a series of shock-melted Yamato-79 LL-chondrites to investigate their late thermal history and the chemical features of shock processes. All meteorites show similarities in shock ages (~ 1.2 Ga) as confirmed by Rb-Sr internal isochron and K-Ar dating, rare gas compositions as well as cosmic-ray exposure ages (~28 Ma), petrographie textures, and sampling sites in Antarctica. These results indicate that all of these meteorites are part of the same fall. The 1.2 Ga shock event caused a severe (partial to total) melting followed by recrystallization of olivine and clinopyroxene, vesiculation, shock-induced alkali homogenization, and local isotopic equilibration or perturbation of the Rb-Sr system. The degrees of shock effects are variable from specimen to specimen and from portion to portion, even in a single specimen. Model calculations of Fe diffusion in olivine suggest that hot and cold materials were in close contact in the impact ejecta sheets of the parent body. From these model calculations and the evidence provided by cosmogenic rare gas compositions, it is concluded that an impact melt ejecta pile composed of hot and cold brecciated materials had formed at depth (> 2 m, shielded from cosmic rays) in an impact crater by the 1.2 Ga event. The parent body was fragmented to meter-size stones by an additional collision at ~28 Ma resulting in the formation of the parent material of the Yamato-79 shocked chondrites.

AB - The Sr and rare gas isotopic compositions and abundances of lithophile trace elements (K, Rb, Sr, Ba, and REEs) were determined for a series of shock-melted Yamato-79 LL-chondrites to investigate their late thermal history and the chemical features of shock processes. All meteorites show similarities in shock ages (~ 1.2 Ga) as confirmed by Rb-Sr internal isochron and K-Ar dating, rare gas compositions as well as cosmic-ray exposure ages (~28 Ma), petrographie textures, and sampling sites in Antarctica. These results indicate that all of these meteorites are part of the same fall. The 1.2 Ga shock event caused a severe (partial to total) melting followed by recrystallization of olivine and clinopyroxene, vesiculation, shock-induced alkali homogenization, and local isotopic equilibration or perturbation of the Rb-Sr system. The degrees of shock effects are variable from specimen to specimen and from portion to portion, even in a single specimen. Model calculations of Fe diffusion in olivine suggest that hot and cold materials were in close contact in the impact ejecta sheets of the parent body. From these model calculations and the evidence provided by cosmogenic rare gas compositions, it is concluded that an impact melt ejecta pile composed of hot and cold brecciated materials had formed at depth (> 2 m, shielded from cosmic rays) in an impact crater by the 1.2 Ga event. The parent body was fragmented to meter-size stones by an additional collision at ~28 Ma resulting in the formation of the parent material of the Yamato-79 shocked chondrites.

UR - http://www.scopus.com/inward/record.url?scp=0025600591&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0025600591&partnerID=8YFLogxK

U2 - 10.1016/0016-7037(90)90301-Z

DO - 10.1016/0016-7037(90)90301-Z

M3 - Article

AN - SCOPUS:0025600591

VL - 54

SP - 3509

EP - 3523

JO - Geochmica et Cosmochimica Acta

JF - Geochmica et Cosmochimica Acta

SN - 0016-7037

IS - 12

ER -