Noble gases in enstatite chondrites I: Exposure ages, pairing, and weathering effects

Patzer, A.; Schultz, L.

doi:10.1111/j.1945-5100.2001.tb01932.x

Cited by 57 publications

(55 citation statements)

References 47 publications

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“…L chondrites in our collections have cosmic ray exposure ages of <70 Ma (Patzer and Schultz 2001). Many of these meteorites are probably derived from a body (or bodies) that formed as a rubble pile by gravitational reassembly of the fragments produced in the catastrophic disruption of a preexisting L-chondrite body.…”

Section: Origin On An L-group Parent Bodymentioning

confidence: 99%

Petrographic classification of Middle Ordovician fossil meteorites from Sweden

Bridges

Schmitz

Hutchison

et al. 2007

Meteorit & Planetary Scien

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Abstract-The maximum diameter of chromite (FeCr 2 O 4 ) grains within L chondrites reflects the petrographic type of the sample. On the basis of our measurements of nine recent L chondrites, L3 chromite D max = 34-50 μm, L4 = 87-150 μm, L5 = 76-158 μm, and L6 = 253-638 μm. This variation reflects the crystallization of the chromite grains during parent body thermal metamorphism.We use this calibration to classify six fossil meteorites from the Middle Ordovician in Sweden as type 3 (or 4) to 6. The high flux of L chondrites at 470 Ma contained a range of petrographic types and may have had a higher proportion of lower petrographic type meteorites than are found in recent L chondrite falls. The fossil meteorites have in places preserved recognizable chondrule textures, including porphyritic olivine, barred olivine, and radiating pyroxene. A large relict clast and fusion crust have also been tentatively identified in one fossil meteorite. Apart from chromite, all of the original meteorite minerals have been replaced by carbonate (and sheet silicate and sulfate) during diagenesis within the limestone host. The preservation of chondrule definition has allowed us to measure the mean diameters of relict chondrules. The range (0.4-0.6 mm) is consistent with measurements made in the same way on recent L chondrites.

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Section: Origin On An L-group Parent Bodymentioning

confidence: 99%

Petrographic classification of Middle Ordovician fossil meteorites from Sweden

Bridges

Schmitz

Hutchison

et al. 2007

Meteorit & Planetary Scien

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“…As for the case (1), cosmogenic-He/Ne data fit into the Bern plot ( Fig. 8; Eberhardt et al, 1966;Nishiizumi et al, 1980;Patzer and Schultz, 2001 21 Ne C excesses observed in small samples. For case of (2), the 21 Ne C production rate varies with target element chemistry.…”

mentioning

confidence: 54%

Trapped noble gas components and exposure history of the enstatite chondrite ALH84206

Nakashima

Nakamura

2006

Geochem. J.

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Noble gases in the Allan Hills (ALH) 84206 EH3 chondrite were measured with stepwise heating of a large sample (98.9 mg) and with total extraction of small samples (0.9-2.3 mg). Light noble gases show solar and cosmogenic components. The elemental ratios of solar gases in the samples suggest no significant loss of solar 36 Ar. Some of small samples are richer in cosmogenic 21 Ne than the large sample. Assuming that the excesses are due to a parent body exposure to cosmic rays, we obtain a parent body exposure age longer than 51 Ma and a meteoroid exposure age shorter than 39 Ma. Heavy noble gases are dominated by elementally fractionated Q-gases and atmospheric noble gases. The presence of fractionated Q-gases combined with no loss of solar 36 Ar suggests that solar wind exposure occurred after Q-gas fractionation. Kr isotopic ratios show the presence of neutron-induced 80 Kr and 82 Kr from Br. The minimum radius of the ALH84206 meteoroid was calculated as 27 cm from the abundances of neutron-induced Kr, assuming that these were produced during exposure of the meteoroid.Keywords: enstatite chondrite, regolith breccia, solar noble gas, primordial noble gas, cosmic-ray exposure age etrates 1 m or so (Walker, 1980), and produces cosmogenic noble gases via spallation reactions with target elements. Grains at the surface regolith are mixed by repeated impacts of cosmic dust and meteoroids (Housen et al., 1979) and acquire solar and cosmogenic noble gases. Cosmic dust bombardment produces tiny iron particles on the surface of the silicate grains via reduction of FeO (Sasaki et al., 2001), which results in darkening of regolith grains (Keller and McKay, 1997). Thus, the grains of the surface regolith darken and are loaded with the solar and cosmogenic noble gases (i.e., irradiated grains). The deeper sited grains below GCR active zone acquire neither solar nor cosmogenic noble gases (i.e., unirradiated grains). After the admixture of unirradiated grains to irradiated grains and residence in a deep site to which even GCR can not penetrate, all the grains within a meteoroid are ejected from the parent body upon a large-scale impact. During transit to the earth, all the grains accumulate cosmogenic noble gases by the exposure to GCR. Although the meteoroid is exposed also to SW and SEP, solar particles implanted on the meteoroid surface are lost during atmospheric entry. Thus, light portions contain only cosmogenic noble gases due to shielding from the solar radiation. Dark portions contain solar and cosmogenic noble gases, and have been part of the sur- INTRODUCTIONA subset of brecciated meteorites contains solar noble gases (Suess et al., 1964;Signer, 1964), indicative of direct exposure to the solar wind. It is generally agreed that the brecciated meteorites originate from surface regoliths of parental asteroids (Wänke, 1965;Lal and Rajan, 1969;Pellas et al., 1969;Wilkening, 1971;Pellas, 1972;Schultz et al., 1972;Rajan, 1974;Anders, 1975;Housen et al., 1979;Keil, 1982;Goswami et al., 1984). Such brecciated meteori...

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“…2). Heavily weathered chondrites are often more contaminated by atmospheric Kr than Xe, thus their Kr/Xe ratios are elevated from the chondritic composition (e.g., Scherer et al, 1994;Patzer and Schultz, 2001 Fig. 3 (Marti, 1967 …”

Section: Noble Gas Resultsmentioning

confidence: 99%

“…Ca and Fe concentrations play a significant role in the calculation of T 38 ages using the equation of Eugster (1988). There is also the possibility that 38 Ar was lost during weathering as pointed out for E-chondrites by Okazaki et al (2000) and Patzer and Schultz (2001). Because the Towada meteorite was found at about 10 years after falling , it could have lost part of 38 Ar during alteration on Earth.…”

Section: Cosmogenic Light Noble Gases and Cosmic-ray Exposure Agesmentioning

confidence: 99%

“…This could have resulted in the loss of cosmogenic 38 Ar. According to Patzer and Schultz (2001) and Scherer et al (1994) Marti and Graf (1992). The data in Nagao et al (1993) mainly produced from Mg in silicate phases, and they are relatively resistant to weathering, we adopt the T 21 as the exposure age of the Towada meteorite.…”

Section: Cosmogenic Light Noble Gases and Cosmic-ray Exposure Agesmentioning

confidence: 99%

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Noble gas and oxygen isotopic compositions of Towada H6-chondrite from Aomori Prefecture, Japan

et al. 2003

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Noble gases in enstatite chondrites I: Exposure ages, pairing, and weathering effects

Cited by 57 publications

References 47 publications

Petrographic classification of Middle Ordovician fossil meteorites from Sweden

Petrographic classification of Middle Ordovician fossil meteorites from Sweden

Trapped noble gas components and exposure history of the enstatite chondrite ALH84206

Noble gas and oxygen isotopic compositions of Towada H6-chondrite from Aomori Prefecture, Japan

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