Oxygen three-isotope ratios of silicate particles returned from asteroid Itokawa by the Hayabusa spacecraft: A strong link with equilibrated LL chondrites

Daisuke Nakashima, Noriko T. Kita, Takayuki Ushikubo, Takaaki Noguchi, Tomoki Nakamura, John W. Valley

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

Oxygen three-isotope ratios of four mineral phases (olivine, low-Ca and high-Ca pyroxene, and plagioclase) in seven silicate particles from asteroid Itokawa were measured to investigate oxygen isotope systematics of asteroidal materials. In order to obtain highly precise and accurate oxygen isotope ratios (~±0.3‰ in δ18O), we used a new indium mounting method that minimizes potential instrumental mass fractionation due to surface topography. The oxygen isotope data of the seven Itokawa particles are distributed above the terrestrial fractionation line with indistinguishable δO17(=δO17-0.52×δO18) values of +1.34±0.36‰ (2SD; n=22), which is similar to those of Itokawa particles analyzed by Yurimoto et al. (2011) and Nakamura et al. (2012). However, δ18O values of the seven Itokawa particles are tightly clustered (+3.9‰ to +5.9‰ VSMOW) compared to previous analyses of the Itokawa particles (+1.4‰ to +8.8‰).The average δ17O values and 2SD of the two equilibrated ordinary chondrites (EOCs), which were analyzed for comparison, are +1.31±0.49‰ for St. Séverin (LL6) and +0.83±0.64‰ for Guareña (H6). The δ17O values of the seven Itokawa particles are similar to those of St. Séverin. The average bulk δ18O value of the seven Itokawa particles is estimated as +4.8‰, which is within the δ18O range of bulk LL5 and LL6 chondrites. It is suggested that Itokawa particles are similar to those of equilibrated LL chondrites, which strengthens a link between asteroid Itokawa and equilibrated LL chondrites that fell to Earth.The seven Itokawa particles and two EOCs have δ18O values of high-Ca pyroxene that are lower than those of olivine, indicating that oxygen isotopes between the two mineral phases are not in equilibrium. Apparent oxygen isotope equilibrium temperatures estimated from a pair of low-Ca pyroxene and olivine are excessively higher than those from a pair of plagioclase and high-Ca pyroxene (~800°C) and peak metamorphic temperatures. Oxygen isotopes in olivine and low-Ca pyroxene do not represent equilibrium. On the other hand, oxygen isotope ratios in high-Ca pyroxene and plagioclase were mass-dependently fractionated accompanied by recrystallization (and possibly by diffusion) during thermal metamorphism. Values of δ18O in high-Ca pyroxene were lowered by exchange, which may have resulted in the reverse δ18O fractionation between olivine and high-Ca pyroxene.

Original languageEnglish
Pages (from-to)127-136
Number of pages10
JournalEarth and Planetary Science Letters
Volume379
DOIs
Publication statusPublished - Sep 9 2013

Fingerprint

Oxygen Isotopes
Silicates
Asteroids
chondrites
isotope ratios
asteroids
chondrite
Isotopes
asteroid
Spacecraft
oxygen isotopes
silicates
pyroxene
spacecraft
silicate
isotope
Oxygen
oxygen
olivine
oxygen isotope

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Oxygen three-isotope ratios of silicate particles returned from asteroid Itokawa by the Hayabusa spacecraft : A strong link with equilibrated LL chondrites. / Nakashima, Daisuke; Kita, Noriko T.; Ushikubo, Takayuki; Noguchi, Takaaki; Nakamura, Tomoki; Valley, John W.

In: Earth and Planetary Science Letters, Vol. 379, 09.09.2013, p. 127-136.

Research output: Contribution to journalArticle

@article{aad51a2ee5f142699191d0a8282b82d6,
title = "Oxygen three-isotope ratios of silicate particles returned from asteroid Itokawa by the Hayabusa spacecraft: A strong link with equilibrated LL chondrites",
abstract = "Oxygen three-isotope ratios of four mineral phases (olivine, low-Ca and high-Ca pyroxene, and plagioclase) in seven silicate particles from asteroid Itokawa were measured to investigate oxygen isotope systematics of asteroidal materials. In order to obtain highly precise and accurate oxygen isotope ratios (~±0.3‰ in δ18O), we used a new indium mounting method that minimizes potential instrumental mass fractionation due to surface topography. The oxygen isotope data of the seven Itokawa particles are distributed above the terrestrial fractionation line with indistinguishable δO17(=δO17-0.52×δO18) values of +1.34±0.36‰ (2SD; n=22), which is similar to those of Itokawa particles analyzed by Yurimoto et al. (2011) and Nakamura et al. (2012). However, δ18O values of the seven Itokawa particles are tightly clustered (+3.9‰ to +5.9‰ VSMOW) compared to previous analyses of the Itokawa particles (+1.4‰ to +8.8‰).The average δ17O values and 2SD of the two equilibrated ordinary chondrites (EOCs), which were analyzed for comparison, are +1.31±0.49‰ for St. S{\'e}verin (LL6) and +0.83±0.64‰ for Guare{\~n}a (H6). The δ17O values of the seven Itokawa particles are similar to those of St. S{\'e}verin. The average bulk δ18O value of the seven Itokawa particles is estimated as +4.8‰, which is within the δ18O range of bulk LL5 and LL6 chondrites. It is suggested that Itokawa particles are similar to those of equilibrated LL chondrites, which strengthens a link between asteroid Itokawa and equilibrated LL chondrites that fell to Earth.The seven Itokawa particles and two EOCs have δ18O values of high-Ca pyroxene that are lower than those of olivine, indicating that oxygen isotopes between the two mineral phases are not in equilibrium. Apparent oxygen isotope equilibrium temperatures estimated from a pair of low-Ca pyroxene and olivine are excessively higher than those from a pair of plagioclase and high-Ca pyroxene (~800°C) and peak metamorphic temperatures. Oxygen isotopes in olivine and low-Ca pyroxene do not represent equilibrium. On the other hand, oxygen isotope ratios in high-Ca pyroxene and plagioclase were mass-dependently fractionated accompanied by recrystallization (and possibly by diffusion) during thermal metamorphism. Values of δ18O in high-Ca pyroxene were lowered by exchange, which may have resulted in the reverse δ18O fractionation between olivine and high-Ca pyroxene.",
author = "Daisuke Nakashima and Kita, {Noriko T.} and Takayuki Ushikubo and Takaaki Noguchi and Tomoki Nakamura and Valley, {John W.}",
year = "2013",
month = "9",
day = "9",
doi = "10.1016/j.epsl.2013.08.009",
language = "English",
volume = "379",
pages = "127--136",
journal = "Earth and Planetary Science Letters",
issn = "0012-821X",
publisher = "Elsevier",

}

TY - JOUR

T1 - Oxygen three-isotope ratios of silicate particles returned from asteroid Itokawa by the Hayabusa spacecraft

T2 - A strong link with equilibrated LL chondrites

AU - Nakashima, Daisuke

AU - Kita, Noriko T.

AU - Ushikubo, Takayuki

AU - Noguchi, Takaaki

AU - Nakamura, Tomoki

AU - Valley, John W.

PY - 2013/9/9

Y1 - 2013/9/9

N2 - Oxygen three-isotope ratios of four mineral phases (olivine, low-Ca and high-Ca pyroxene, and plagioclase) in seven silicate particles from asteroid Itokawa were measured to investigate oxygen isotope systematics of asteroidal materials. In order to obtain highly precise and accurate oxygen isotope ratios (~±0.3‰ in δ18O), we used a new indium mounting method that minimizes potential instrumental mass fractionation due to surface topography. The oxygen isotope data of the seven Itokawa particles are distributed above the terrestrial fractionation line with indistinguishable δO17(=δO17-0.52×δO18) values of +1.34±0.36‰ (2SD; n=22), which is similar to those of Itokawa particles analyzed by Yurimoto et al. (2011) and Nakamura et al. (2012). However, δ18O values of the seven Itokawa particles are tightly clustered (+3.9‰ to +5.9‰ VSMOW) compared to previous analyses of the Itokawa particles (+1.4‰ to +8.8‰).The average δ17O values and 2SD of the two equilibrated ordinary chondrites (EOCs), which were analyzed for comparison, are +1.31±0.49‰ for St. Séverin (LL6) and +0.83±0.64‰ for Guareña (H6). The δ17O values of the seven Itokawa particles are similar to those of St. Séverin. The average bulk δ18O value of the seven Itokawa particles is estimated as +4.8‰, which is within the δ18O range of bulk LL5 and LL6 chondrites. It is suggested that Itokawa particles are similar to those of equilibrated LL chondrites, which strengthens a link between asteroid Itokawa and equilibrated LL chondrites that fell to Earth.The seven Itokawa particles and two EOCs have δ18O values of high-Ca pyroxene that are lower than those of olivine, indicating that oxygen isotopes between the two mineral phases are not in equilibrium. Apparent oxygen isotope equilibrium temperatures estimated from a pair of low-Ca pyroxene and olivine are excessively higher than those from a pair of plagioclase and high-Ca pyroxene (~800°C) and peak metamorphic temperatures. Oxygen isotopes in olivine and low-Ca pyroxene do not represent equilibrium. On the other hand, oxygen isotope ratios in high-Ca pyroxene and plagioclase were mass-dependently fractionated accompanied by recrystallization (and possibly by diffusion) during thermal metamorphism. Values of δ18O in high-Ca pyroxene were lowered by exchange, which may have resulted in the reverse δ18O fractionation between olivine and high-Ca pyroxene.

AB - Oxygen three-isotope ratios of four mineral phases (olivine, low-Ca and high-Ca pyroxene, and plagioclase) in seven silicate particles from asteroid Itokawa were measured to investigate oxygen isotope systematics of asteroidal materials. In order to obtain highly precise and accurate oxygen isotope ratios (~±0.3‰ in δ18O), we used a new indium mounting method that minimizes potential instrumental mass fractionation due to surface topography. The oxygen isotope data of the seven Itokawa particles are distributed above the terrestrial fractionation line with indistinguishable δO17(=δO17-0.52×δO18) values of +1.34±0.36‰ (2SD; n=22), which is similar to those of Itokawa particles analyzed by Yurimoto et al. (2011) and Nakamura et al. (2012). However, δ18O values of the seven Itokawa particles are tightly clustered (+3.9‰ to +5.9‰ VSMOW) compared to previous analyses of the Itokawa particles (+1.4‰ to +8.8‰).The average δ17O values and 2SD of the two equilibrated ordinary chondrites (EOCs), which were analyzed for comparison, are +1.31±0.49‰ for St. Séverin (LL6) and +0.83±0.64‰ for Guareña (H6). The δ17O values of the seven Itokawa particles are similar to those of St. Séverin. The average bulk δ18O value of the seven Itokawa particles is estimated as +4.8‰, which is within the δ18O range of bulk LL5 and LL6 chondrites. It is suggested that Itokawa particles are similar to those of equilibrated LL chondrites, which strengthens a link between asteroid Itokawa and equilibrated LL chondrites that fell to Earth.The seven Itokawa particles and two EOCs have δ18O values of high-Ca pyroxene that are lower than those of olivine, indicating that oxygen isotopes between the two mineral phases are not in equilibrium. Apparent oxygen isotope equilibrium temperatures estimated from a pair of low-Ca pyroxene and olivine are excessively higher than those from a pair of plagioclase and high-Ca pyroxene (~800°C) and peak metamorphic temperatures. Oxygen isotopes in olivine and low-Ca pyroxene do not represent equilibrium. On the other hand, oxygen isotope ratios in high-Ca pyroxene and plagioclase were mass-dependently fractionated accompanied by recrystallization (and possibly by diffusion) during thermal metamorphism. Values of δ18O in high-Ca pyroxene were lowered by exchange, which may have resulted in the reverse δ18O fractionation between olivine and high-Ca pyroxene.

UR - http://www.scopus.com/inward/record.url?scp=84883381989&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84883381989&partnerID=8YFLogxK

U2 - 10.1016/j.epsl.2013.08.009

DO - 10.1016/j.epsl.2013.08.009

M3 - Article

AN - SCOPUS:84883381989

VL - 379

SP - 127

EP - 136

JO - Earth and Planetary Science Letters

JF - Earth and Planetary Science Letters

SN - 0012-821X

ER -