Argon-Potassium Ages and the Isotopec Composition of Argon from Meteorites.

Geiss, J.; Hess, David C.

doi:10.1086/146453

Cited by 99 publications

(21 citation statements)

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“…The 39 Ar-40 Ar ages of stepped extractions of Ar from a whole rock were variable, but similar to the value of Geiss and Hess (1958). The 39 Ar-40 Ar ages of stepped extractions from a plagioclase separate were approximately constant and gave a good age plateau at 254±10 Myr.…”

Section: The Shergottites: Late Amazonian Volcanismsupporting

confidence: 55%

“…We begin our discussion with early Mars, working towards the present day. References: a1 Geiss and Hess (1958), recalculated to the K-decay constants by Steiger and Jäger (1977); a Eugster et al (1997a); b Bogard et al (1979); c Bogard and Garrison (1999); d Nyquist et al (1979a); e Jagoutz and Wänke (1986); f Shih et al (1982); g Chen and Wasserburg (1986); h Sano et al (2000); i Nyquist et al (1995); j Nyquist et al (2000); k Nyquist et al (1986); l Nyquist et al (2001); m Borg et al (1997); n Borg et al (2000); o , Jagoutz and Jotter (2000); p Miura et al (1995); q Jagoutz (1989); r Borg et al (2001b); s,t Borg et al (1998aBorg et al ( , 1998b; u Chen and Wasserburg (1993); v Misawa et al (1997); w Terribilini et al (1998).…”

Section: Radiometric Agesmentioning

confidence: 99%

“…The first radiometric age for a meteorite now considered to be of Martian origin was the K-Ar age of 580 ± 50 Myr (recalculated with the decay parameters by Steiger and Jäger, 1977) determined for Shergotty by Geiss and Hess (1958) in an early study of the K-Ar ages of stony meteorites. Geiss and Hess (1958) considered their age to be "too young". They excluded the possibilities of K contamination or heterogeneity in the K content of the meteorite.…”

Section: The Shergottites: Late Amazonian Volcanismmentioning

confidence: 99%

“…The young radiometric ages of shergottites, first observed for the type example, Shergotty, by Geiss and Hess (1958), were among the first lines of evidence cited in support of their origin on a planetary-sized body, probably Mars (Nyquist et al, 1979b;Wasson and Wetherill, 1979). However, some characteristics of the analytical data seemed to violate criteria developed for unambiguous interpretation of radiometric ages as igneous crystallizaton ages.…”

Section: Introductionmentioning

confidence: 97%

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Ages and Geologic Histories of Martian Meteorites

Nyquist

Bogard

Shih

et al. 2001

Space Sciences Series of ISSI

376

558

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Abstract.We review the radiometric ages of the 16 currently known Martian meteorites, classified as 11 shergottites (8 basaltic and 3 lherzolitic), 3 nakhlites (clinopyroxenites), Chassigny (a dunite), and the orthopyroxenite ALH84001. The basaltic shergottites represent surface lava flows, the others magmas that solidified at depth. Shock effects correlate with these compositional types, and, in each case, they can be attributed to a single shock event, most likely the meteorite's ejection from Mars. Peak pressures in the range 15 − 45 GPa appear to be a "launch window": shergottites experienced ∼30 − 45 GPa, nakhlites ∼20 ± 5 GPa, Chassigny ∼35 GPa, and ALH84001 ∼35 − 40 GPa. Two meteorites, lherzolitic shergottite Y-793605 and orthopyroxenite ALH84001, are monomict breccias, indicating a two-phase shock history in toto: monomict brecciation at depth in a first impact and later shock metamorphism in a second impact, probably the ejection event.Crystallization ages of shergottites show only two pronounced groups designated S 1 (∼175 Myr), including 4 of 6 dated basalts and all 3 lherzolites, and S 2 (330 − 475 Myr), including two basaltic shergottites and probably a third according to preliminary data. Ejection ages of shergottites, defined as the sum of their cosmic ray exposure ages and their terrestrial residence ages, range from the oldest (∼20 Myr) to the youngest (∼0.7 Myr) values for Martian meteorites. Five groups are distinguished and designated S Dho (one basalt, ∼20 Myr), S L (two lherzolites of overlapping ejection ages, 3.94 ± 0.40 Myr and 4.70 ± 0.50 Myr), S (four basalts and one lherzolite, ∼2.7 − 3.1 Myr), S DaG (two basalts, ∼1.25 Myr), and S E (the youngest basalt, 0.73 ± 0.15 Myr). Consequently, crystallization age group S 1 includes ejection age groups S L , S E and 4 of the 5 members of S, whereas S 2 includes the remaining member of S and one of the two members of S DaG . Shock effects are different for basalts and lherzolites in group S/S 1 . Similarities to the dated meteorite DaG476 suggest that the two shergottites that are not dated yet belong to group S 2 . Whether or not S 2 is a single group is unclear at present. If crystallization age group S 1 represents a single ejection event, pre-exposure on the Martian surface is required to account for ejection ages of S L that are greater than ejection ages of S, whereas secondary breakup in space is required to account for ejection ages of S E less than those of S. Because one member of crystallization age group S 2 belongs to ejection group S, the maximum number of shergottite ejection events is 6, whereas the minimum number is 2.Crystallization ages of nakhlites and Chassigny are concordant at ∼1.3 Gyr. These meteorites also have concordant ejection ages, i.e., they were ejected together in a single event (NC). Shock effects vary within group NC between the nakhlites and Chassigny.The orthopyroxenite ALH84001 is characterized by the oldest crystallization age of ∼4.5 Gyr. Its secondary carbonates are ∼3.9 Gyr old, an age corresponding t...

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Section: The Shergottites: Late Amazonian Volcanismsupporting

confidence: 55%

Section: Radiometric Agesmentioning

confidence: 99%

Section: The Shergottites: Late Amazonian Volcanismmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

See 2 more Smart Citations

Ages and Geologic Histories of Martian Meteorites

Nyquist

Bogard

Shih

et al. 2001

Space Sciences Series of ISSI

376

558

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“…The same instruments as in Odessa are used for double-station photographs in Kiev during the I.G.Y. Results are published in [25][26][27][28] and descriptions of the methods in [29][30][31][32].The meteor base Ondfejov-Prclce was further developed; as well as ten unguided cameras at each station with rotating shutters, at one station a new patrol system of thirteen guided cameras was put into operation. Also experiments with two 'long focus' cameras with f.c.…”

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confidence: 99%

22. Commission des Meteores et des Meteorites

Guth¹

1960

Trans. Int. Astron. Union

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The past triennium has been characterized by further developments in meteor astronomy, and the following results have been obtained:(1) The majority of meteors, whether photographic and visual or radar and telescopic, show a strong preference for direct motion near the ecliptic inside the solar system.(2) Meteors are connected with comets and their orbits have the same distribution as those of comets.(3) Meteorites are connected with the system of minor planets; micro-meteorites with the zodiacal light.(4) The structure of a few showers and their ages have been determined. These results are based on improved observational methods (photographic, radar and telescopic observation in connexion with visual observations).Great progress has also been made in the physical theory of meteors, although many unknown parameters permit different interpretations of the new theories. I.G.Y. measurements directly in the ' meteor surroundings' (artificial satellites and meteors) will contribute to the removal of the fundamental discrepancies which exist today. We shall then know even better the interaction between the atmosphere and meteors.The detailed description of results obtained is presented below. O B S E R V A T I O N A L M E T H O D SRadar observations of meteors were made in the following countries: Australia. Radio-echo rates for both shower and sporadic meteors have been systematically measured from 1952 at Adelaide with the 27 Mc/s C.W. equipment. Meteors above limiting brightness in the range M R + y-$ are regularly registered. A. A. Weiss discusses the sporadic background [1], shower meteors [2] and the influx of meteor particles over the whole surface of the Earth and their density in space [3]. The results are in good agreement with those obtained at other radio stations.Canada. A new meteor observatory was erected in 1957 at Springhill (20 miles southsouth-east of Ottawa) where the programme of meteor research using a combination of radio, photographic and visual techniques was transferred from Metcalf Road Field M E T E O R E S E T M E T E O R I T E SStation. A 32 Mc/s meteor radar with peak power of 400 kW and single-dipole antenna system has been built specially for the I.G.Y. meteor programme. In addition to this a special 32 Mc/s I.G.Y. meteor radar with peak power near 20 kW and omni-directional antennas is operated continuously throughout the I.G.Y. [4].Czechoslovakia. The first Czechoslovak radar was finished in 1957. It works on a frequency of 37-5 Mc/s with peak power of 25 kW and with a rotating antenna system (14 x 6 m; the beam-width to the half-power points is +16° in the horizontal plane and ± 27° in the vertical plane) at an elevation of 45 0 . The radar is now being tested. Great Britain. The radio survey of meteor activity has been continued at the Jodrell Bank Station of the University of Manchester with the same equipment as before. Important results on meteor physics have been obtained. U.S.A.A system of megawatt transmitter and six receiving stations are proposed to be operated during the ...

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Le dosage du potassium des météorites par dilution isotopique, et la détermination de leur âge par la méthode K/A

Krummenacher¹

1961

Helvetica Chimica Acta

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Die erwahnte PdC1,-Struktur unterscheidet sich von derjenigen des CrCI, nur dadurch, dass die Elementarzelle in der a-Richtung stark auseinandergezogen ist, wodurch die (4 + 2)-Koordination in eine planare Vierer-Koordination iibergeht (Pd-4Cl in 2,31 A). Schliesslich kristallisiert auch CaCl, im gleichen Typ wie CrCl,, nur ist dort das Koordinationsoktaeder praktisch unverzerrt (Ca-4C1 in 2,76, A, Ca-2C1 in 2,70 A : v. REVEK 8r NIETJWENKAMP~~)). Verdankungen. Herrn Prof. Dr. W. FEITKNECHT danken wir fur sein reges Interesse und fur die Durchsicht des Manuskripts. Herrn Dr. Y. IITAKA sei bestens gedankt fur die uberlassung der Maschinen-Programme zur Berechnung der F, und der Parameter-Verfeinerung. Dem Institut fur angewandte Mathematik der Universitat Bern (Herm Prof. W. NEP) verdanken wir die Erlaubnis zur Reniitzung der elektronischen Rechenmaschine. SUMMAKYThe crystal structure of anhydrous chromium dichloride (CrCl,) has been determined by the X-ray powder method. CrC1, has an orthorhombic elementary cell with a = 6,624 f 0,006 A, b = 5,974 f 0,006 A, c = 3,488 f 0,004 fi, space group D$!,-Pnnm. The values for the only free parameters xcl and yc, have been refined by a least squares treatment. The structure of CrC1, is related to the PdCI, structure and, as expected from the crystal field theory, to the structure of CuC1,. Each Cr atom is surrounded nearly quadratically by four C1 atoms at a distance of 2,37, A and two C1 atoms at 2,91 A, completing a deformed octahedron.

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Argon-Potassium Ages and the Isotopec Composition of Argon from Meteorites.

Cited by 99 publications

References 0 publications

Ages and Geologic Histories of Martian Meteorites

Ages and Geologic Histories of Martian Meteorites

22. Commission des Meteores et des Meteorites

Le dosage du potassium des météorites par dilution isotopique, et la détermination de leur âge par la méthode K/A

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