Cosmic-Ray Exposure Ages of Meteorites

Herzog, G. F.; Caffee, Marc W.

doi:10.1016/b978-0-08-095975-7.00110-8

Cited by 86 publications

(173 citation statements)

References 204 publications

(225 reference statements)

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“…) are similar (~10–12 Ma; Fritz et al. ; Herzog ; Eugster et al. ; McSween ; as of this writing ejection ages have not yet been determined for the most recently recovered nakhlites).…”

Section: Introductionmentioning

confidence: 71%

“…This suggests that most or all eight presently known nakhlite meteorites (along with the chassignites, which have similar crystallization and ejection ages as the nakhlites, but are outside the scope of this paper) not only have essentially identical igneous crystallization ages but were also ejected together, most likely from the same source locality on Mars, at a different time than the ejection of most other Mars meteorites (used here to mean “meteorites from Mars” rather than “meteorites found on Mars”; ejection ages from Fritz et al. ; Herzog ; Eugster et al. ; McSween ).…”

Section: Introductionmentioning

confidence: 98%

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Modal abundances of pyroxene, olivine, and mesostasis in nakhlites: Heterogeneity, variation, and implications for nakhlite emplacement

Corrigan

Velbel

Vicenzi

2015

Meteorit & Planetary Scien

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Nakhlites, clinopyroxenite meteorites from Mars, share common crystallization and ejection ages, suggesting that they might have been ejected from the same place on Mars by the same ejection event (impact) and are different samples of the same thick volcanic flow unit or shallow sill. Mean modal abundances and abundance ranges of pyroxene, olivine, and mesostasis vary widely among different thin-sections of an individual nakhlite. Lithologic heterogeneity is the main factor contributing to the observed modalabundance variations measured in thin-sections prepared from different fragments of the same stone. Two groups of nakhlites are distinguished from one another by which major constituent varies the least and the abundance of that constituent. The group consisting of Nakhla, Lafayette, Governador Valadares, and the Yamato nakhlite pairing group is characterized by low modal mesostasis and pyroxene-olivine covariance, whereas the group consisting of the Miller Range nakhlite pairing group and Northwest Africa 5790 is characterized by low modal olivine and pyroxene-mesostasis covariance. These two groups sample the slowest-cooled interior portion and the chilled margin, respectively, of the nakhlite emplacement body as presently understood, and appear to be also related to recently proposed nakhlite groups independently established using compositional rather than petrographic observations. Phenocryst modal abundances vary with inferred depth in the nakhlite igneous body in a manner consistent with solidification of the nakhlite stack from dynamically sorted phenocryst-rich magmatic crystal-liquid mush.

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“…) are similar (~10–12 Ma; Fritz et al. ; Herzog ; Eugster et al. ; McSween ; as of this writing ejection ages have not yet been determined for the most recently recovered nakhlites).…”

Section: Introductionmentioning

confidence: 71%

Section: Introductionmentioning

confidence: 98%

Modal abundances of pyroxene, olivine, and mesostasis in nakhlites: Heterogeneity, variation, and implications for nakhlite emplacement

Corrigan

Velbel

Vicenzi

2015

Meteorit & Planetary Scien

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“…Purely empirically, we note that all measured cosmic ray exposure age estimates for Martian meteorites range between about 0.5 to 20 Ma. For the different type shergottites these exposure ages lie between 0.73 and 18 Ma; for ALH84001 it is 14.2 Ma, and for a cluster of nakhalite/chassignites, at ~11.0 Myr [ Herzog and Caffee , ]. Our team studied six other young Martian craters with detectable broad infrared rays, with diameters from 2.6 to 29 km, and derived ages in the range of 0.1 to 30 Myr [ Hartmann et al ., ].…”

Section: Implication For Crater Count Chronologymentioning

confidence: 99%

Young Martian crater Gratteri and its secondary craters

et al. 2016

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In response to questions that have been raised about formation and effects of secondary craters on crater chronometry techniques, we studied properties of the secondary crater field around the young Martian primary ray crater Gratteri (diameter 7 km). The crater has an estimated age of 1 to 20 Myr, based on counts of small craters on flat interior surface, consistent with a likely age for a young crater its size (Hartmann et al., 2010). The following are among our findings: (1) We identify an unusual class of craters we call “rampart secondaries” which may suggest low‐angle impacts. (2) We measure size distributions of secondaries as a function of distance from Gratteri and used these data to reconstruct the mass‐velocity distribution of ejecta blasted out of Gratteri. Our data suggest that crater density in rays tends to peak around 120–230 km from Gratteri (roughly 20–30D) and reaches roughly 30–70 times the interray crater density. (3) Comparable total numbers of secondaries form inside rays and outside rays, and about half are concentrated in clusters in 2% of the area around Gratteri, with the others scattered over 98% of the area out to 400 km away from Gratteri. (4) In the old Noachian plains around Gratteri, secondaries have minimal effect on crater chronometry. These results, along with recently reported direct measurements of the rate of formation of 10 m to 20 m primaries on Mars (Daubar et al., 2013), tend to negate suggestions that the numbers and/or clustering of secondaries destroy the effectiveness of crater counting as a chronometric tool.

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“…As discoveries of Martian meteorites continue to be made (especially in northwestern Africa, “NWA”), the number of unpaired specimens keeps increasing (at least 80 in 2015; Irving ). Prior to the results reported here, about half of these specimens had been analyzed for cosmogenic nuclides (see Herzog and Caffee and references therein; Cartwright et al. ), although the exact number of impacts to produce these meteorites remains controversial.…”

Section: Introductionmentioning

confidence: 99%

“…), although the exact number of impacts to produce these meteorites remains controversial. Herzog and Caffee () favored five distinct events launching the 30 shergottites reported in their database, likely one event for eight nakhlites, one for orthopyroxenite ALH 84001, and one for impact melt breccia NWA 7034 (and paired stones from Rabt Sbayta, Morocco; Bouragaa et al. ).…”

Section: Introductionmentioning

confidence: 99%

Noble gases in 18 Martian meteorites and angrite Northwest Africa 7812—Exposure ages, trapped gases, and a re‐evaluation of the evidence for solar cosmic ray‐produced neon in shergottites and other achondrites

Wieler

Huber

Busemann

et al. 2016

Meteorit & Planetary Scien

106

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We present noble gas data for 16 shergottites, 2 nakhlites (NWA 5790, NWA 10153), and 1 angrite (NWA 7812). Noble gas exposure ages of the shergottites fall in the 1–6 Ma range found in previous studies. Three depleted olivine‐phyric shergottites (Tissint, NWA 6162, NWA 7635) have exposure ages of ~1 Ma, in agreement with published data for similar specimens. The exposure age of NWA 10153 (~12.2 Ma) falls in the range of 9–13 Ma reported for other nakhlites. Our preferred age of ~7.3 Ma for NWA 5790 is lower than this range, and it is possible that NWA 5790 represents a distinct ejection event. A Tissint glass sample contains Xe from the Martian atmosphere. Several samples show a remarkably low (21Ne/22Ne)cos ratio < 0.80, as previously observed in a many shergottites and in various other rare achondrites. This was explained by solar cosmic ray‐produced Ne (SCR Ne) in addition to the commonly found galactic cosmic ray‐produced Ne, implying very low preatmospheric shielding and ablation loss. We revisit this by comparing measured (21Ne/22Ne)cos ratios with predictions by cosmogenic nuclide production models. Indeed, several shergottites, acalpulcoites/lodranites, angrites (including NWA 7812), and the Brachina‐like meteorite LEW 88763 likely contain SCR Ne, as previously postulated for many of them. The SCR contribution may influence the calculation of exposure ages. One likely reason that SCR nuclides are predominantly detected in meteorites from rare classes is because they usually are analyzed for cosmogenic nuclides even if they had a very small (preatmospheric) mass and hence low ablation loss.

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Cosmic-Ray Exposure Ages of Meteorites

Cited by 86 publications

References 204 publications

Modal abundances of pyroxene, olivine, and mesostasis in nakhlites: Heterogeneity, variation, and implications for nakhlite emplacement

Modal abundances of pyroxene, olivine, and mesostasis in nakhlites: Heterogeneity, variation, and implications for nakhlite emplacement

Young Martian crater Gratteri and its secondary craters

Noble gases in 18 Martian meteorites and angrite Northwest Africa 7812—Exposure ages, trapped gases, and a re‐evaluation of the evidence for solar cosmic ray‐produced neon in shergottites and other achondrites

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