Cosmic ray exposure ages of tektites by the fission-track technique

AbstractThe cosmic ray exposure ages of deep sea metalic lie spherules were determined by various methods; low level countings (Ni-59), neutron activation analysis (Mn-53), high energy accelerator mass spectrometry (Be-10, Al-26) and mass spectrometry (K isotopes). The exposure ages of 0.3 - 50 Ma were obtained. According to Poynting-Robertson effect, the starting points (supplying sources) are located at inner region of the orbit of Saturn.

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Long-term galactic cosmic ray variations over the last billion years based on the cosmic-ray exposure ages of iron meteorites

Geochemistry International ◽

10.1134/s001670291601002x ◽

2016 ◽

Vol 54 (1) ◽

pp. 78-84 ◽

Cited By ~ 2

Author(s):

V. A. Alexeev

Keyword(s):

Cosmic Ray ◽

Iron Meteorites ◽

Galactic Cosmic Ray ◽

Exposure Ages ◽

Cosmic Ray Exposure Ages

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Noble Gas Record of Japanese Chondrites

Zeitschrift für Naturforschung A ◽

10.1515/zna-1989-1006 ◽

1989 ◽

Vol 44 (10) ◽

pp. 935-944

Author(s):

Nobuo Takaoka ◽

Masako Shima ◽

Fumitaka Wakabayashi

Keyword(s):

Noble Gas ◽

Cosmic Ray ◽

Ordinary Chondrites ◽

Isotopic Signatures ◽

Shock Heating ◽

H Chondrites ◽

Gas Loss ◽

Exposure Ages ◽

Cosmic Ray Exposure Ages ◽

Gas Component

Abstract Concentrations and isotopic ratios of noble gases are reported for nineteen Japanese chondrites. Among those, Nio (H3-4) is a solar-gas-rich meteorite.U/Th - He ages are younger than K - Ar ages for all meteorites studied. Six of the nine L-chondrites give significantly young K-Ar ages, suggesting gas loss by impact shock heating. The remaining three L-chondrites and seven of the ten H-chondrites have K-Ar ages older than 4 Ga. The L-chondrite Nogata and the H-chondrites Numakai, Ogi and Higashi-Koen have concordant ages.Cosmic-ray exposure ages for six of the H-chondrites show clustering around the 6-Myr peak in the distribution of exposure ages, while those for the L-chondrites, ranging from 8.2 to 64 Myr, do not show clustering.Fukutomi (L4) contains trapped 36Ar in excess, 3.5 times enriched compared to the highest value so far reported for type-4 ordinary chondrites except solar-gas-rich chondrites. The 36Ar/132Xe and 84Kr/132Xe ratios fit along a mixing line between a planetary and a sub-solar (or argon-rich) component found in separates of E-chondrites [43], The Xe isotopic composition is identical with that in Abee and Kenna. The isotopic signatures suggest that this meteorite may contain mineral fragments bearing the noble gas component found in E-chondrites or ureilites. Fukutomi also contains 80Kr, 82Kr and 128Xe produced by epithermal neutron captures on 79Kr, 81Kr and 127I, respectively. From the neutron-produced Kr, the preatmospheric minimum radius is estimated to be 20 cm with an assumption of a spherical meteoroid.

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3. Fragmentation of Asteroids and Delivery of Fragments to Earth

International Astronomical Union Colloquium ◽

10.1017/s0252921100070184 ◽

1977 ◽

Vol 39 ◽

pp. 283-291 ◽

Cited By ~ 1

Author(s):

G. W. Wetherill

Keyword(s):

Cosmic Ray ◽

Asteroid Belt ◽

Combined Effects ◽

Iron Meteorites ◽

Exposure Age ◽

Impact Rate ◽

Dynamical Time ◽

Spectrophotometric Data ◽

Exposure Ages ◽

Cosmic Ray Exposure Ages

Earth-impacting meteoroids are derived from both comets and asteroids, and some uncertainty still exists regarding with which of these bodies some stone meteorites should be identified. In contrast, the long cosmic ray exposure ages of iron meteorites strongly suggest a long-lived asteroidal source capable of providing ~108 g/yr of this material to the earth’s surface over at least much of solar system history. Spectrophotometric data show that differentiated asteroids are concentrated in the inner portion of the asteroid belt. The orbital histories of fragments of inner belt asteroids are investigated, considering the combined effects of close planetary encounters, secular perturbations, and secular resonances. Particular attention is given to the low inclination (<15°) objects with small semimajcr axis (2.1 to 2.6 A.U.), which can make fairly close approaches to Mars (<0.1 A.U.). It is found that the annual yield and dynamical lifetime of collision fragments of these asteroids is in agreement with the observed impact rate and exposure age of iron meteorites. A smaller yield of stone meteorites (-107 g/yr) is expected, because elimination of these objects by collision is probable on the long dynamical time scaTe. Achondrites could be produced in this way; the yield is probably too low to account for chondrites. Chondrites could possibly be derived indirectly from these bodies insofar as these asteroids are also sources of Apollo and Amor objects.

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