The clay-size fraction of CI chondrites Alais and Orgueil : an AEM study

Mackinnon, Ian D.R. & Kaser, Stacey A. (1988) The clay-size fraction of CI chondrites Alais and Orgueil : an AEM study. In Lunar and Planetary Science Conference, Lunar and Planetary Institute, Houston, Texas, USA, pp. 709-710.

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Abstract

CI chondrites are used pervasively in the meteorite literature as a cosmochemical reference point for bulk compositions[1], isotope analyses[2] and, within certain models of meteorite evolution, as an important component of an alteration sequence within the carbonaceous chondrite subset[3]. More recently, the chemical variablity of CI chondrite matrices (which comprise >80% of the meteorite), has been cited in discussions about the "chondritic" nature of spectroscopic data from P/comet Halley missions[4] and of chemical data from related materials such as interplanetary dust particles[5]. Most CI chondrites have been studied as bulk samples(e.g. major and trace element abundances)and considerable effort has also been focussed on accessory phases such as magnetites, olivine, sulphates and carbonates [6-8]. A number of early studies showed that the primary constituents of CI matrices are layer silicates and the most definitive structural study on powdered samples identified two minerals: montmorillonite and serpentine[9]. In many cases, as with the study by Bass[9],the relative scarcity of most CI chondrites restricts such bulk analyses to the Orgueil meteorite. The electron microprobe/SEM has been used on petrographic sections to more precisely define the "bulk" composition of at least four CI matrices[3], and as recently summarised by McSween[3], these data define a compositional trend quite different to that obtained for CM chondrite matrices. These "defocussed-beam" microprobe analyses average major element compositions over matrix regions ~lOOµm in diameter and provide only an approximation to silicate mineral composition(s) because their grain sizes are much less than the diameter of the beam. In order to (a) more precisely define the major element compositions of individual mineral grains within CI matrices, and (b)complement previous TEM studies [11,12], we have undertaken an analytical electron microscopy (AEM) study of Alais and Orgueil matrices.

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ID Code: 55678
Item Type: Conference Paper
Refereed: Yes
Additional Information: GeoRef, Copyright 2009, American Geological Institute.
1989-076329
Alais Meteorite
Ivuna Meteorite
Keywords: carbonaceous chondrites, chondrites, CI chondrites, comets, composition, Halley's Comet, interplanetary dust, interpretation, major elements, metals, meteorites, minor elements, models, nickel, Orgueil Meteorite, SEM data, silicates, stony meteorites, sulfur, TEM data, textures
Subjects: Australian and New Zealand Standard Research Classification > EARTH SCIENCES (040000) > GEOLOGY (040300) > Extraterrestrial Geology (040302)
Australian and New Zealand Standard Research Classification > EARTH SCIENCES (040000) > GEOLOGY (040300) > Mineralogy and Crystallography (040306)
Divisions: Current > Institutes > Institute for Future Environments
Copyright Owner: Copyright 1988 Lunar and planetary Institute
Deposited On: 21 Jan 2013 06:27
Last Modified: 09 Apr 2013 20:33

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