26Al survey of Antarctic meteorites

Evans, J. C.; Reeves, J. H.

doi:10.1016/0012-821x(87)90197-x

Cited by 22 publications

(15 citation statements)

References 13 publications

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“…The 26Aland 22Na activities are typical for an L chondrite, for which normal values fall near 59 ± 8 dpm/kg for 26Al (Evans and Reeves, 1987) and 60-110 dpm/kg for 22Na (Evans et al, 1982). Worden fell near the most recent solar minimum in 1997, and the 22Na production rate should have been at a level approaching the maximum levels due to solar modulation of the galactic cosmic-ray flux.…”

Section: Resultsmentioning

confidence: 99%

“…Calibration procedures for 26Al were the same as used for the analysis of Antarctic meteorites (Edwards et al, 1982;Evans and Reeves, 1987), which uses a calibration curve based on our extensive library ofmockups offreshly fallen meteorites. For 22Na and 60Co, a series of mockups were used to calibrate the instrument in a fashion similar to that used for 26AI.…”

Section: Resultsmentioning

confidence: 99%

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The Worden meteorite: A new ordinary chondrite fall from Michigan, USA

Velbel

Matty

Wacker

et al. 2002

Meteorit & Planetary Scien

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Abstract-An ordinary chondrite fall in southeast Michigan, USA (near the crossroads hamlet of Worden in northeast Washtenaw County) penetrated the garage roof of a private home on 1997 September 1. The Worden chondrite comprises silicate matrix, mineral fragments, chondrules, chondrule fragments, and opaque primary phases. Electron microprobe analyses (olivine, Fa23.9; orthopyroxene, FS20.l, En78.8, W01) indicate diagnostic L-chondrite silicate mineral compositions. Recognizable chondrules and chondrule fragments constitute up to 42 vol%. Chondrule boundaries are readily discernable (especially where chondrules have rims of opaque material) but not sharp, and discrete plagioclase crystals are visible in the devitrified mesostasis of barred olivine chondrules; together, these characteristics suggest petrologic type 5. The spatially averaged ensemble of shockrelated features (optical extinction of olivine grains, minor localized shock melt) suggests assignment of a shock stage of S3.The 26Al and 22Na activities are typical for an L chondrite. Worden fell near the most recent solar minimum in 1997, and the 22Na production rate should have been at a level approaching the maximum levels due to solar modulation of the galactic cosmic-ray flux. The low value for the Worden 22Na activity relative to those observed in chondrite falls associated with the 1969 solar maximum and 1976 solar minimum suggests a relatively small preatmospheric size. The 60Co activity confirms the indication ofa small body. The 56Co activity was essentially zero, indicating that none ofthe recovered meteorite contained material exposed to solar cosmic rays.The Worden chondrite is the fourth documented fall in Michigan, and the fourth stony meteorite recovered in Michigan; all other Michigan meteorites are finds, not observed falls, and are iron meteorites. All Michigan falls to date are ordinary chondrites. The three falls prior to Worden were Allegan (H5) fell 1899; Rose City (H5, brecciated, black (dark matrix)) fell 1921 ; and Coleman (L6, veined (shocked); Osborn et a!., 1997) fell 1994. Worden has a much lighter matrix than Rose City, and is less extensively thermally and shock metamorphosed than either Rose City (Steffler et a!., 1991) or Coleman.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

The Worden meteorite: A new ordinary chondrite fall from Michigan, USA

Velbel

Matty

Wacker

et al. 2002

Meteorit & Planetary Scien

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“…Normalized to L-chondrite composition, the 26AI-contents range from 27 to 110 dpm/kg with peaks around 43 and 53 dpm/kg. This bimodal 26AI distribution is reminiscent of that observed for Allan Hills ordinary chondrites (Evans and Reeves, 1987). Tentative terrestrial ages, calculated on the basis 0[26Al saturation levels of 56 ± 7 and 60 ± ?for H-and L-chondrites respectively (Vogt, 1990), range up to 800 ka, with an average of about 290 ka.…”

Section: Atmospheric Drag On Ring Particlesmentioning

confidence: 95%

Abstracts

1992

Meteoritics

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“…I dpmlkg, compared to average values of 54.5 2 0.6 dpm/kg for 558 OCs from the whole Allan Hills area and of 53.4 2 0.7 dpm/kg for 366 OCs from the Main Allan Hills Ice Field only (Evans and Reeves, 1987;Grossman, 1994). The errors represent a/*.…”

Section: Aluminum-26 Gamma-ray Surveymentioning

confidence: 99%

Terrestrial ages of ordinary chondrites from the Lewis Cliff stranding area, East Antarctica

Welten

Lindner

Alderliesten

et al. 1999

Meteorit & Planetary Scien

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Abstract-We determined terrestrial ages of ordinary chondrites from the Lewis Cliff stranding area, East Antarctica, on the basis of the concentrations of cosmogenic loge (ts = 1.5 1 Ma), 26A1 (ts = 0.705 Ma), and 36Cl (t% = 0.301 Ma). After an initial 26A1 pray survey of 91 meteorites suggested that many have terrestrial ages >O. 1 Ma, we selected 62 meteorites for 1OBe and 26A1 measurements by accelerator mass spectrometry (AMS) and measured 36Cl in twelve of those. Low terrestrial ages (<0.1 Ma) were found for -60% of the meteorites, whereas all others have ages between 0.1 and 0.5 Ma, except for one exceptional age of >2 Ma (Welten et al., 1997). Our major conclusions are: (1) The Lewis Cliff H-chondrites show similar ages to those from the Allan Hills icefields, but the L-chondrites are about a factor of 2 younger than those from Allan Hills, which indicates that Lewis Cliff is a younger stranding area. (2) The terrestrial age distributions at different parts of the Lewis Cliff stranding area generally agree with simple meteorite concentration models, although differences in weathering rate may also play a role. (3) We confirm that meteorites with natural thermoluminescence (TL) levels >SO h a d are associated with low terrestrial ages (Benoit et ul., 1992) but conclude that natural TL levels <80 h a d can not be used to calculate the terrestrial age of a meteorite. Natural TL levels do seem useful to estimate relative terrestrial ages of large groups of meteorites and to determine differences in the surface exposure age of paired meteorite fragments. (4) Of the 62 meteorites measured with AMS, 3 1 were assigned to 1 1 different pairing groups, mainly on the basis of their cosmogenic nuclide record. The meteorites are estimated to represent between 42 and 52 distinct falls.

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26Al survey of Antarctic meteorites

Cited by 22 publications

References 13 publications

The Worden meteorite: A new ordinary chondrite fall from Michigan, USA

The Worden meteorite: A new ordinary chondrite fall from Michigan, USA

Abstracts

Terrestrial ages of ordinary chondrites from the Lewis Cliff stranding area, East Antarctica

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