Rb–Sr isotopic systematics of alkali-rich fragments in the Yamato-74442 LL-chondritic breccia

Yokoyama, T.; Misawa, K.; Okano, Osamu; Shih, C.-Y.; Nyquist, L. E.; Simon, Justin I.; Tappa, M. J.; Yoneda, Shigekazu

doi:10.1016/j.epsl.2013.01.037

Cited by 5 publications

(31 citation statements)

References 30 publications

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“…(), and Bouvier () are similar to ages reported by Yokoyama et al. () for alkali‐rich clasts from the Yamato‐74442 LL chondritic breccia. Their interpretation was that the clasts formed by impact of alkali‐enriched glasses and alkali‐poor chondritic material and record an ancient age for impact melting.…”

Section: Discussionsupporting

confidence: 86%

“…An identically old U-Pb age of (4454 AE 67 Ma) for Cl-apatites was also reported by Lapen et al (2014). The~4.45 Ga ages reported by Lapen et al (2014), Popova et al (2013), andBouvier (2013) are similar to ages reported by Yokoyama et al (2013) for alkali-rich clasts from the Yamato-74442 LL chondritic breccia. Their interpretation was that the clasts formed by impact of alkali-enriched glasses and alkali-poor chondritic material and record an ancient age for impact melting.…”

Section: Agessupporting

confidence: 78%

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Mineralogy, petrology, chronology, and exposure history of the Chelyabinsk meteorite and parent body

Righter¹,

Abell²,

Agresti

et al. 2015

Meteorit & Planetary Scien

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Three masses of the Chelyabinsk meteorite have been studied with a wide range of analytical techniques to understand the mineralogical variation and thermal history of the Chelyabinsk parent body. The samples exhibit little to no postentry oxidation via Mössbauer and Raman spectroscopy indicating their fresh character, but despite the rapid collection and care of handling some low levels of terrestrial contamination did nonetheless result. Detailed studies show three distinct lithologies, indicative of a genomict breccia. A light‐colored lithology is LL5 material that has experienced thermal metamorphism and subsequent shock at levels near S4. The second lithology is a shock‐darkened LL5 material in which the darkening is caused by melt and metal‐troilite veins along grain boundaries. The third lithology is an impact melt breccia that formed at high temperatures (~1600 °C), and it experienced rapid cooling and degassing of S2 gas. Portions of light and dark lithologies from Chel‐101, and the impact melt breccias (Chel‐102 and Chel‐103) were prepared and analyzed for Rb‐Sr, Sm‐Nd, and Ar‐Ar dating. When combined with results from other studies and chronometers, at least eight impact events (e.g., ~4.53 Ga, ~4.45 Ga, ~3.73 Ga, ~2.81 Ga, ~1.46 Ga, ~852 Ma, ~312 Ma, and ~27 Ma) are clearly identified for Chelyabinsk, indicating a complex history of impacts and heating events. Finally, noble gases yield young cosmic ray exposure ages, near 1 Ma. These young ages, together with the absence of measurable cosmogenic derived Sm and Cr, indicate that Chelyabinsk may have been derived from a recent breakup event on an NEO of LL chondrite composition.

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Section: Discussionsupporting

confidence: 86%

Section: Agessupporting

confidence: 78%

Mineralogy, petrology, chronology, and exposure history of the Chelyabinsk meteorite and parent body

Righter¹,

Abell²,

Agresti

et al. 2015

Meteorit & Planetary Scien

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“…Except in CI-carbonaceous chondrites, alkalis are depleted in Earth, Moon, Mars, Vesta and all meteorites, suggesting that the entire inner solar system was more or less depleted in moderately volatile elements. Very alkali-rich materials have been observed in silicate inclusions in IIE iron meteorites (Burnett and Wasserburg, 1967;Sanz et al, 1970), in howardites as impact spherules (Barrat et al, 2009) and in few chondritic breccias, such as Krähenberg (LL5), Bhola (LL3-6), Yamato(Y)-74442 (LL4) and Acfer111 (H3-6) (Kempe and Müller, 1969;Wlotzka et al, 1983Wlotzka et al, , 1992Yokoyama et al, 2013). Since the fragments in Krähenberg and Y-74442 are highly enriched in rubidium, the Rb-Sr isotopic systematics have been used to constrain chemical characteristics of their source materials (Kempe and Müller, 1969;Yokoyama et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

“…Previous investigations revealed that alkali elements in Krähenberg, Bhola and Acfer 111 rock fragments are fractionated relative to CI-chondrites with heavier alkalis in general being more enriched (Kempe and Müller, 1969;Wlotzka et al, 1983Wlotzka et al, , 1992. The alkalirich rock fragments in Y-74442 also are relatively enriched in potassium, up to 15 x CIchondrites (Yokoyama et al, 2013), enabling the study of its K-Ca isotopic systematics.…”

Section: Introductionmentioning

confidence: 99%

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Extreme early solar system chemical fractionation recorded by alkali-rich clasts contained in ordinary chondrite breccias

Yokoyama

Misawa

Okano

et al. 2017

Earth and Planetary Science Letters

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New K-Ca and Rb-Sr isotopic analyses have been performed on alkali-rich igneous rock fragments in the Yamato (Y)-74442 and Bhola LL-chondritic breccias to better understand the extent and timing of alkali enrichments in the early solar system. The Y-74442 fragments yield a K-Ca age of 4.41 ± 0.28 Ga for λ(40 K) = 0.5543 Ga-1 with an initial 40 Ca/ 44 Ca ratio of 47.1618 ± 0.0032. Studying the same fragments with the Rb-Sr isotope system yields an age of 4.420 ± 0.031 Ga for λ(87 Rb) = 0.01402 Ga-1 with an initial ratio of 87 Sr/ 86 Sr = 0.7203 ± 0.0044. An igneous rock fragment contained in Bhola shows a similar alkali fractionation pattern to those of Y-74442 fragments but does not plot on the K-Ca or Rb-Sr isochron of the Y-74442 fragments. Calcium isotopic compositions of whole-rock samples of angrite and chondrites are primordial, indistinguishable from mantle-derived terrestrial rocks, and here considered to represent the initial composition of bulk silicate Earth. The initial ε 40 Ca value determined for the source of the alkali clasts in Y-74442 that is ~0.5 ε-units higher than the solar system value implies an early alkali enrichment. Multi-isotopic studies on these alkali-rich fragments reveal that the source material of Y-74442 fragments had elemental ratios of K/Ca = 0.43 ± 0.18, Rb/Sr = 3.45 ± 0.66 and K/Rb ~170, that may have formed from mixtures of an alkali-rich component (possibly an alkali-enriched gaseous reservoir produced by fractionation of early nebular condensates) and chondritic components that were flash-heated during an impact event on the LLchondrite parent body ~4.42 Ga ago. Further enrichments of potassium and rubidium relative to calcium and strontium as well as a mutual alkali-fractionation (K/Rb ~50 and 3/25 differentiation of this melt. Alkali fragments in Bhola might have undergone similar solidvapor fractionation processes to those of Y-74442 fragments but appear to have formed via a distinct impact melting event.

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Photostimulated luminescence applicable to pre-screening of potassium-rich phases in chondritic breccias

Yokoyama

Misawa

Okano

et al. 2016

J Radioanal Nucl Chem

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Rb–Sr isotopic systematics of alkali-rich fragments in the Yamato-74442 LL-chondritic breccia

Cited by 5 publications

References 30 publications

Mineralogy, petrology, chronology, and exposure history of the Chelyabinsk meteorite and parent body

Mineralogy, petrology, chronology, and exposure history of the Chelyabinsk meteorite and parent body

Extreme early solar system chemical fractionation recorded by alkali-rich clasts contained in ordinary chondrite breccias

Photostimulated luminescence applicable to pre-screening of potassium-rich phases in chondritic breccias

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