title: Niobium-zirconium chronometry and early solar system development.
abstract: Niobium-92 (92Nb) decays to zirconium-92 (92Zr) with a half-life of 36 million years and can be used to place constraints on the site of p-process nucleosynthesis and the timing of early solar system processes. Recent results have suggested that the initial 92Nb/93Nb of the solar system was high (>10(-3)). We report Nb-Zr internal isochrons for the ordinary chondrite Estacado (H6) and a clast of the mesosiderite Vaca Muerta, both of which define an initial 92Nb/93Nb ratio of approximately 10(-5). Therefore, the solar system appears to have started with a ratio of <3 x 10(-5), which implies that Earth's initial differentiation need not have been as protracted as recently suggested.
authors.affiliation: Institute of Isotope Geology and Mineral Resources, ETH Zürich, 8092 Zürich, Switzerland. maria@erdw.ethz.ch
authors.forename: Maria
authors.initials: M
authors.lastname: Schönbächler
authors.forename: Mark
authors.initials: M
authors.lastname: Rehkämper
authors.forename: Alex N
authors.initials: AN
authors.lastname: Halliday
authors.forename: Der-Chuen
authors.initials: DC
authors.lastname: Lee
authors.forename: Michèle
authors.initials: M
authors.lastname: Bourot-Denise
authors.forename: Brigitte
authors.initials: B
authors.lastname: Zanda
authors.forename: Bodo
authors.initials: B
authors.lastname: Hattendorf
authors.forename: Detlef
authors.initials: D
authors.lastname: Günther