Special Issue: The Kobe meteorite consortium—Preface

Nakamura, Noboru

doi:10.2343/geochemj.36.289

“…The total mass of recovered stones is 136 g. They are now in the possession of Mr. Hirata. Two pieces (17 g in total mass) were loaned from him for consortium studies (Nakamura, 2002). A small fragment, 8 mm in largest dimension, was provided to us.…”

Section: Introductionmentioning

confidence: 99%

The Kobe CK carbonaceous chondrite: petrography, mineralogy and metamorphism

Tomeoka

¹

,

Kojima

²

,

Ishii

³

et al. 2005

Journal of Mineralogical and Petrological Sciences

Self Cite

View full text Add to dashboard Cite

A petrographic and mineralogical study of Kobe indicates that it can be classified as a CK4 carbonaceous chondrite. CK chondrites differ from other groups of carbonaceous chondrites, because all normal CK chondrites have been thermally metamorphosed. Olivine and plagioclase are the two most abundant minerals in Kobe. Olivine is very homogeneous in composition, which is consistent with the metamorphic feature of Kobe. However, plagioclase shows large grain to grain compositional variations. The matrix and chondrule mesostases exhibit pronounced silicate darkening. They contain unusual olivine that contains numerous small vesicles (< 0.1 3 μm in diameter) and inclusions (< 0.1 10 μm) of magnetite, pentlandite and minor plagioclase, pyroxene and chlorapatite. The vesicular olivine is particularly abundant in regions that exhibit a high degree of darkening. The vesicular olivine is clearly the principal cause of the silicate darkening. Plagioclase in matrix and chondrule mesostases also contains numerous small vesicles and inclusions of magnetite, pyroxene and minor pentlandite and olivine. The texture and mineralogy of the vesicular olivine and plagioclase suggest that they recrystallized from melts that were produced from olivine and plagioclase in the matrix by shock. We suggest that the shock event occurred at a relatively mild pressure and a high temperature, probably at the state where the meteorite underwent thermal metamorphism.

show abstract

“…Two large fragments, Kobe C (14.5 g) and Kobe E (3.7 g), were loaned to us by their finder for the purpose of scientific analysis. Petrographic, chemical, and isotopic descriptions of the Kobe meteorite have been published previously by a consortium of laboratories from Japan and the USA (Nakamura, 2002). The meteorite is classified as a metamorphosed Karoonda type carbonaceous chondrite (CK4) (Tomeoka et al, 2001(Tomeoka et al, , 2005.…”

Section: Introductionmentioning

confidence: 99%

Structural state of plagioclase from the Kobe CK chondrite: Implications for the thermal history of the CK parent body

NAKAMUTA¹,

NAKAMURA²,

NAKAMURA³

2006

Journal of Mineralogical and Petrological Sciences

Self Cite

0

View full text Add to dashboard Cite

We determined the structural state of six plagioclase crystals from the Kobe meteorite by measuring the separation between the 13 1 and 131 X ray diffraction peaks (Δ131 parameter) using a Gandolfi camera. The formation temperature of each plagioclase crystal was then estimated by plotting the Δ131 parameter on the relation diagram between the Δ131 parameters and temperatures of plagioclase synthesis, as proposed by Smith (1972). Three of the crystals record temperatures of just under 700 °C, while the other three crystals record much lower temperatures. The temperature estimates can be regarded as representing the crystallization temperature of plagioclase, and the highest recorded temperature is thought to correspond to the peak temperature of the thermal metamorphism, close to but not exceeding 700 °C. A thermal model of the CK chondrites is proposed on the assumption that thermal metamorphism, with 26 Al decay as a heat source, began prior to accretion of the CK parent body. The model explains the homogeneous compositions of olivine and pyroxene in CK chondrites, which are inconsistent with the petrographic type suggested by their grain sizes, and explains the occurrence of silicate darkening in almost all CK chondrites.

show abstract

Structural state of plagioclase from the Kobe CK chondrite: Implications for the thermal history of the CK parent body

Nakamuta

¹

,

Nakamura

²

,

Nakamura

³

2006

Journal of Mineralogical and Petrological Sciences

Self Cite

View full text Add to dashboard Cite

We determined the structural state of six plagioclase crystals from the Kobe meteorite by measuring the separation between the 13 1 and 131 X ray diffraction peaks (Δ131 parameter) using a Gandolfi camera. The formation temperature of each plagioclase crystal was then estimated by plotting the Δ131 parameter on the relation diagram between the Δ131 parameters and temperatures of plagioclase synthesis, as proposed by Smith (1972). Three of the crystals record temperatures of just under 700 °C, while the other three crystals record much lower temperatures. The temperature estimates can be regarded as representing the crystallization temperature of plagioclase, and the highest recorded temperature is thought to correspond to the peak temperature of the thermal metamorphism, close to but not exceeding 700 °C. A thermal model of the CK chondrites is proposed on the assumption that thermal metamorphism, with 26 Al decay as a heat source, began prior to accretion of the CK parent body. The model explains the homogeneous compositions of olivine and pyroxene in CK chondrites, which are inconsistent with the petrographic type suggested by their grain sizes, and explains the occurrence of silicate darkening in almost all CK chondrites.

show abstract

Special Issue: The Kobe meteorite consortium—Preface

Cited by 3 publications

References 9 publications

The Kobe CK carbonaceous chondrite: petrography, mineralogy and metamorphism

The Kobe CK carbonaceous chondrite: petrography, mineralogy and metamorphism

Structural state of plagioclase from the Kobe CK chondrite: Implications for the thermal history of the CK parent body

Structural state of plagioclase from the Kobe CK chondrite: Implications for the thermal history of the CK parent body

Contact Info

Product

Resources

About