Origin of zoned metal grains in the QUE94411 chondrite

Citation
Aj. Campbell et al., Origin of zoned metal grains in the QUE94411 chondrite, GEOCH COS A, 65(1), 2001, pp. 163-180
Citations number
51
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Earth Sciences
Journal title
GEOCHIMICA ET COSMOCHIMICA ACTA
ISSN journal
0016-7037 → ACNP
Volume
65
Issue
1
Year of publication
2001
Pages
163 - 180
Database
ISI
SICI code
0016-7037(200101)65:1<163:OOZMGI>2.0.ZU;2-L
Abstract
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to measure distributions of the siderophile elements P, V. Cr, Fe, Co , Ni, Mo, Ru, Rh, Pd, W, Re, Os, Ir, and Pt in metal grains in the metal-ri ch chondrite QUE94411 with a spatial resolution of similar to 30 mum. The p latinum group elements (PGEs), except Pd, exhibit radial zoning in these gr ains that mimics that previously observed in Ni and Co; the concentrations of these elements decreases from the cores to the rims of the grains. The P GE distributions support a condensation origin for the enhanced refractory element abundances in the zoned grains; the lack of zoning in Pd refutes an origin by a redox-controlled process, and none of the PGE-Ni relationships support an origin by fractional crystallization from a metallic melt. Seve ral models of grain formation were explored, including equilibrium fraction al condensation, which failed to yield the correct radial zoning. The zonin g may be the product of a nonequilibrium fractional condensation process, i n which the refractory siderophiles remained supersaturated in the cooling solar nebula, or of diffusion between refractory-enhanced Fe-Ni cores and o ther Fe-Ni metal that may have been deposited later from the solar nebula. Copyright (C) 2001 Elsevier Science Ltd.