Ages and composition of gas trapped in Allan Hills and Byrd core ice

Fireman, E. L.; Norris, T. L.

doi:10.1016/0012-821x(82)90072-3

Cited by 55 publications

(22 citation statements)

References 13 publications

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“…3). This is despite the fact that 8180 of ice in the region is about -40% (Fireman and Norris, 1982). Ferric alteration correlates 1 : 1 with loss of silicates (Fig.…”

Section: Resultsmentioning

confidence: 84%

“…To model alteration on the CV parent body, and to observe the effect of alteration on the 0-isotopic composition of meteorites, we chose L-group ordinary chondrite finds as analog samples, recovered from hot deserts and the Allan Hills (ALH) region of Antarctica (chosen because the 0-isotopic composition of the ice is known; Fireman and Norris, 1982). Aside from having a nonterrestrial 0 composition, L chondrites have similar Fe-metal, oxide, and sulphide abundances to CV chondrites (Sears and Dodd, 1988).…”

Section: Samples and Experimental Methodsmentioning

confidence: 99%

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Aqueous alteration without a pronounced oxygen‐isotopic shift: Implications for the asteroidal processing of chondritic materials

Bland

Lee

Sexton

et al. 2000

Meteorit & Planetary Scien

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Abstract-Primitive meteorites exhibit certain features that are consistent with aqueous and thermal alteration on asteroids, but 0-isotopic analyses show only a modest heavy-isotope shift, interpreted as indicating modification in the nebula. To understand the isotopic effects of asteroidal alteration, we take the L-group ordinary chondrites weathered in Antarctica as an analogue. The data show that alteration is a two-stage process, with an initial phase producing only a negligible isotopic effect. Although surprising, a possible explanation is found when we consider the alteration of terrestrial silicates. Numerous studies report pervasive development of channels a few to a few tens of nanometer wide in the incipient alteration of silicates. We observe a similar texture. Alteration involves a restructuring of clay minerals along these narrow channels, in which access of water is restricted. The clay shows a topotactic relationship to the primary grain, which suggests either epitaxial growth of the clay using the silicate as a substrate or inheritance of the original 0 structure by the clay. Our data suggests the latter: with extensive inheritance of structural polymers by the weathering product, the bulk 0-isotopic composition is comparatively unaffected. This offers an explanation for the lack of an isotopic effect in the weathering of the L chondrites. If substantial modification of chondritic materials may occur without a pronounced isotopic effect, it also reconciles existing 0 analyses of CV chondrites with an asteroidal model of aqueous alteration.

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“…3). This is despite the fact that 8180 of ice in the region is about -40% (Fireman and Norris, 1982). Ferric alteration correlates 1 : 1 with loss of silicates (Fig.…”

Section: Resultsmentioning

confidence: 84%

Section: Samples and Experimental Methodsmentioning

confidence: 99%

Aqueous alteration without a pronounced oxygen‐isotopic shift: Implications for the asteroidal processing of chondritic materials

Bland

Lee

Sexton

et al. 2000

Meteorit & Planetary Scien

View full text Add to dashboard Cite

show abstract

“…analysed the oxygen isotopic composition of a number of samples weathered in Antarctica, meteorites which, as falls, had an initial 18 O value of 4.7x. In the case of ice from the Allan Hills region, from which a large number of meteorites have been recovered, Fireman and Norris (1982) found a d 18 O of about À 40x relative to SMOW, so even a small degree of alteration should lead to a large displacement in the isotopic composition of the meteorite to lower d 18 O values (Clayton et al, 1984). What is surprising is that significant amounts of alteration are required before any isotopic effect is observed.…”

Section: Resultsmentioning

confidence: 96%

Terrestrial weathering rates defined by extraterrestrial materials

Bland

2006

Journal of Geochemical Exploration

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“…Inasmuch as this meteorite was in contact with Antarctic ice [8180 =~--40 per mil(23)] for at least tens of thousands of years before it was collected(24,25), it is plausible that the original 8180 values have been lowered by terrestrial…”

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confidence: 99%

Water in SNC Meteorites: Evidence for a Martian Hydrosphere

Karlsson

Clayton

Gibson

et al. 1992

Science

156

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The Shergotty-Nakhla-Chassigny (SNC) meteorites, purportedly of martian origin, contain 0.04 to 0.4 percent water by weight. Oxygen isotopic analysis can be used to determine whether this water is extraterrestrial or terrestrial. Such analysis reveals that a portion of the water is extraterrestrial and furthermore was not in oxygen isotopic equilibrium with the host rock. Lack of equilibrium between water and host rock implies that the lithosphere and hydrosphere of the SNC parent body formed two distinct oxygen isotopic reservoirs. If Mars was the parent body, the maintenance of two distinct reservoirs may result from the absence of plate tectonics on the planet.

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Ages and composition of gas trapped in Allan Hills and Byrd core ice

Cited by 55 publications

References 13 publications

Aqueous alteration without a pronounced oxygen‐isotopic shift: Implications for the asteroidal processing of chondritic materials

Aqueous alteration without a pronounced oxygen‐isotopic shift: Implications for the asteroidal processing of chondritic materials

Terrestrial weathering rates defined by extraterrestrial materials

Water in SNC Meteorites: Evidence for a Martian Hydrosphere

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