Manioc : Portail | resultats 61 - 80 pour la recherche: Natural history -- Canada.

Voyage géologique aux Antilles et aux îles de Ténériffe et de Fogo. Tome 1
Auteur(s) : Sainte-Claire Deville, Charles (1814-1876)
Année de publication :

| Plus

Trace element geochemistry of CR chondrite metal
Auteur(s) : Jacquet, Emmanuel Paulhiac-Pison, Marine Alard, Olivier T. Kearsley, Anton Gounelle, Matthieu
Auteurs secondaires : Laboratoire de minéralogie du Muséum National d'Histoire Naturelle (LMMNHN) ; Muséum National d'Histoire Naturelle (MNHN) - Centre National de la Recherche Scientifique (CNRS) Canadian Institute for Theoretical Astrophysics, University of Toronto ; Canadian Institute for Theoretical Astrophysics École normale supérieure - Paris (ENS Paris) Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) Impacts and Astromaterials Research Centre, Department of Mineralogy, The Natural History Museum ; Impacts and Astromaterials Research Centre, Department of Mineralogy, Institut Universitaire de France (IUF) ; Ministère de l'Éducation nationale, de l’Enseignement supérieur et de la Recherche (M.E.N.E.S.R.)

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
We report trace element analyses by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of metal grains from nine different CR chondrites, distinguishing grains from chondrule interior ("interior grains"), chondrule surficial shells ("margin grains"), and the matrix ("isolated grains"). Save for a few anomalous grains, Ninormalized trace element patterns are similar for all three petrographic settings, with largely unfractionated refractory siderophile elements and depleted volatile Au, Cu, Ag, S. All three types of grains are interpreted to derive from a common precursor approximated by the least-melted, fine-grained objects in CR chondrites. This also excludes recondensation of metal vapor as the origin of the bulk of margin grains. The metal precursors were presumably formed by incomplete condensation, with evidence for high-temperature isolation of refractory platinum-group-element (PGE)-rich condensates before mixing with lower temperature PGE-depleted condensates. The rounded shape of the Ni-rich, interior grains shows that they were molten and that they equilibrated with silicates upon slow cooling (1-100 K h 1), largely by oxidation/evaporation of Fe, hence their high Pd content, for example. We propose that Ni-poorer, amoeboid margin grains, often included in the pyroxene-rich periphery common to type I chondrules, result from less intense processing of a rim accreted onto the chondrule subsequent to the melting event recorded by the interior grains. This means either that there were two separate heating events, which formed olivine/ interior grains and pyroxene/margin grains, respectively, between which dust was accreted around the chondrule, or that there was a single high-temperature event, of which the chondrule margin records a late "quenching phase," in which case dust accreted onto chondrules while they were molten. In the latter case, high dust concentrations in the chondrule-forming region (at least three orders of magnitude above minimum mass solar nebula models) are indicated.
ISSN: 1086-9379

hal-01003975
https://hal.archives-ouvertes.fr/hal-01003975
DOI : 10.1111/maps.12212

| Plus