On The Problem Of The Isotopic Composition Of Lead In Iron Meteorites

Starik, I. Ye.; Sobotovich, E. V.; Lovtsyus, G. P.; Shats, M. M.; Lovtsyus, A. V.

doi:10.1080/00206816309473821

International Geology Review

1963

DOI: 10.1080/00206816309473821

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On The Problem Of The Isotopic Composition Of Lead In Iron Meteorites

I. Ye. Starik¹,

E. V. Sobotovich²,

G. P. Lovtsyus³

et al.

Abstract: Analyses were made of samples of the several classes of iron meteorites: (hexahedrites, octahedrites, ataxites, and troilite inclusions) in further study of the isotopic composition of primordial lead and toward establishing correlation between the distribution of lead among the mineral inclusions and the nickel-iron mass of the meteorite. Two groups of iron meteorites can be distinguished on the basis of isotopic composition lead suggesting two ages for the parent bodies of common iron meteorites. The distrib… Show more

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“…portion, and i f one makes t h e usual(8) assumptions c onceining t h e primordial l e a d 9 ( 1 ) c: r a t i o s , an age of 4.6 7 1 0 years can be c a l c u l a t e d from t h e d a t a bf S t a r i k e t a 1 . t i .…”

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confidence: 99%

"Ages" of the Sikhote Alin Meteorite

Sisher¹

1962

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Abstract.The potassium-argon age of the Sikhote AUn iron meteorite --9 has been determined. The value i s 1 . 7 + 0.2 x 10 years. Previous lead data suggest an age of 4.6 x 10' ye a r s . The date of solidification m q be the sum of these two ages.Lead isotopic r a t i o s showing an excess of the nuclides lead-206, -207, and -208 relative t o lead-204 have been measured i n several iron meteorites'').A s with such r a t i o s reported f o r stone meteorites, these excesses may represent radiogenic contributions f ram the natural decay of uranium-235, uranium-238, and !thorium-232, respectively. However, i n one of these meteorites, Sikhote Alin, an upper limit was s e t t o the abundance of uranium-235 such that the excess lead-207 10 Tk(2 could not be accounted f o r by uranium decay i n a period l e s s than 10 years . This represents t~o '~~e r s of magnitude too l i t t l e uranium t o agree with the calcu- Ib 9(3 lated lead-lead age of 4.6 x 10 yeaxs .A possible explanation for t h i s uraniun deficiency would be a recent melting and chemical fractionation of the material t h a t i s now the Sikhote AUn meteorite.A suitable method of testing t h i s hypothesis i s by means of potassium-argon dating, since any process capable of removing uranium frcm the meteoritic mass w o u l d also remove the argon. Such an experiment fa reported here, and leads t o a potassium-9 argon "age" of abuut 1 . 7 x 10 yews. This i s significantly less than such ages previausly measured f co. other iron meteorites"),and mqy indicate that a recent melting (or at l e a s t a severe heating) did occur. This i s a necessary but not a suff'icient condition f o r the removal of uranium froan lead.Three separate runs were nade at the Brookhaven Reactor, i n which samples 3-5 2 grams i n size were irradiated f o r three ho~&s a t a flux of 5 x 1 0~ n/m see. , DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document.was placed i n an alumina crucible i n a vacuum l i n e , then boiled by induction heating f o r twenty minutes i n the presence of argon c a r r i e r . The evolved gases were gassed over hot titanium, which was then cooled t o remove hydrogen. The gases were then pumped i n t o a proportional counter with a background of about 10 counts per minute. The chemical y i e l d was 100% i n a l l cases. I n i t i a l counting r a t e s i n t h e three samples varied from 4000 t o 300 counts per minute. The a c t i v i t y followed the argon-41 h a l f -l i f e down t o about 15 cpm, then decayed with the argon-37 h a l f -l i f e be made from the argon-37 a c t i v i t y , which r e s u l t s from the ArJ6(n, r)Ar37 reaction.~r g o n -3 6 i s produced i n meteorites through d i r e c t nuclear production and through the decay of cosmic ray produced chlorine-36. The cross section r a t i o , from i r o n t a r g e t s , of (Ar36 + C 1 3 6 ) /~4 0 i s about 5 ( 5 ) . The correction f o r cosmogenic argon-40 i n this meteorite amounts t o about ...

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"Ages" of the Sikhote Alin Meteorite

Sisher¹

1962

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On The Problem Of The Isotopic Composition Of Lead In Iron Meteorites

Cited by 1 publication

References 3 publications

"Ages" of the Sikhote Alin Meteorite

"Ages" of the Sikhote Alin Meteorite

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