Volatile fractionation in the early solar system and chondrule/matrix complementarity
- Philip A. Bland*,†,‡,
- Olivier Alard§,¶,
- Gretchen K. Benedix*,∥,
- Anton T. Kearsley†,
- Olwyn N. Menzies*,
- Lauren E. Watt*, and
- Nick W. Rogers§
- *Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom; †Impacts and Astromaterials Research Centre, Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom; §Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom; ¶Laboratoire de Tectonophysique, Centre National de la Recherche Scientifique–Institut des Sciences de la Terre, de l'Environnment, et de l'Espace de Montpellier, Université de Montpellier II, 34095 Montpellier, France; and ∥Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130
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Edited by Robert N. Clayton, University of Chicago, Chicago, IL, and approved July 15, 2005 (received for review March 8, 2005)
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Fig. 1.Trace element data derived from LA and solution ICP-MS analyses of matrix in 18 carbonaceous chondrites, ratioed to CI and Yb, with relevant literature data for bulks, rims, chondrules, and matrix (13, 15, 17, 18), ordered in terms of condensation temperature (19). (a) CV3 chondrites. (b) CO3 chondrites. (c) CR2 chondrites and NWA1152. (d) CM2 chondrites. (e) Anomalous and ungrouped chondrites.
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Fig. 2.Data for moderately volatile elements, ordered in a sequence of increasing volatility (lithophiles are indicated by vertical bars; Ni, Au, and Ge are siderophile; all other elements are chalcophile). (a) Average matrix compositions for CV, CO, and CM chondrites. LA-ICP-MS data (and standard deviation in LA analyses) is also shown for CI1 chondrites (Alais and Orgueil). Different chondrite groups have distinct matrix lithophile abundances, which plot close to the bulk data for those groups. CV and CO matrices have very similar siderophile and chalcophile abundances. The elements most fractionated in C3 matrices are siderophiles and chalcophiles; they are significantly enriched over bulk and over matrix lithophiles. (b) Allende and Mighei have representative matrix compositions for CV3 and CM2 chondrites, respectively. LA-ICP-MS and analysis of separated matrix by solution ICP-MS show that their matrices are compositionally distinct. Allende is generally depleted compared with Mighei, and Mighei shows much less variation between siderophile/chalcophile and lithophile elements. Mighei matrix is depleted in all moderately volatile elements compared with CI. Finally, in Allende, chondrule siderophiles and chalcophiles (13) are substantially depleted compared with bulk, complementing enrichment in matrix in these elements.
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Fig. 3.Refractory trace element data, ordered in terms of volatility. Note the linear scale, to highlight any interelement variability in abundance. (a) Matrix data from representative C3 chondrites. C3 chondrites show highly nonmonotonic volatile patterns, but chondrite-normalized (N) refractory/Yb abundances are flat. (b) Data from representative CM chondrite matrices, Tagish Lake, and Bali. Of the eight C3 matrices analyzed, only Bali's shows enrichment in Sr. This enrichment is similar to CM matrix (and matrix in Tagish Lake), which typically shows a departure from chondritic values in Sr. (c) Data from CR2 matrices. This group shows the most evidence for aqueous exchange between chondrules and matrix, with substantial enrichments in Sr and U. The absence of fractionated refractories in C3 matrices with highly nonmonotonic volatile patterns, and the presence of fractionated refractories in C2s with monotonic volatile patterns, suggests that aqueous redistribution is not the mechanism of choice to explain siderophile and chalcophile enrichment in C3 matrices.
Footnotes
- Copyright © 2005, The National Academy of Sciences
