U-Pb systematics in iron meteorites: Uniformity of primordial lead |
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| Authors: | C Göpel G Manhès CJ Allègre |
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| Institution: | Laboratoire de Géochimie et Cosmochimie, Institut de Physique du Globe de Paris et Département des Sciences de la Terre, Universités de Paris VI et VII, 4, Place Jussieu, 75230 Paris cedex 05, France |
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| Abstract: | Pb isotopic compositions and U-Pb abundances were determined in the metal phase of six iron meteorites: Canyon Diablo IA, Toluca IA, Odessa IA, Youndegin IA, Deport IA and Mundrabilla An. Prior to complete dissolution, samples were subjected to a series of leachings and partial dissolutions. Isotopic compositions and abundances of the etched Pb indicate a contamination by terrestrial Pb which is attributable to previous cutting of the meteorite. Pb isotopic compositions measured in the decontaminated samples are identical within 0.2% and essentially confirm the primordial Pb value defined by Tatsumotoet al. (1973). These data invalidate more radiogenic Pb isotopic compositions published for iron meteorites, which are the result of terrestrial Pb contamination introduced mainly by analytical procedure. Our results support the idea of a solar nebula which was isotopically homogeneous for Pb 4.55 Ga ago. The new upper limit for U-abundance in iron meteorites, 0.001 ppb, is in agreement with its expected thermodynamic solubility in the metal phase. |
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