A magmatic origin for silica-rich glass inclusions hosted in porphyritic magnesian olivines in chondrules: an experimental study

1,2François Faure, 1,2Laurent Tissandier, 1,2Léa Florentin, 3,4Karine Devineau
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2017.01.034]
1Université de Lorraine, CRPG, UMR 7358, 15 rue Notre Dame des Pauvres F-54501 Vandoeuvre-lès-Nancy France
2CNRS, CRPG, UMR 7358, 15 rue Notre Dame des Pauvres F-54501 Vandoeuvre-lès-Nancy France
3Université de Lorraine, GeoRessources, UMR 7359, Faculté des Sciences et Technologies rue Jacques Callot BP 70239, F-54506 Vandoeuvre-lès-Nancy Cedex, France
4CNRS, GeoRessources, UMR 7359, Faculté des Sciences et Technologies rue Jacques Callot BP 70239, F-54506 Vandoeuvre-lès-Nancy Cedex, France
Copyright Elsevier

Rare silica-rich glass inclusions (69 < SiO2 < 82 wt.%) are described within magnesian olivines of porphyritic Type IA chondrules. These glass inclusion compositions are clearly out of equilibrium with their host Mg-olivines and their presence within the olivines is generally attributed to an unclear secondary process such as a late interaction with nebular gases. We performed dynamic crystallisation experiments that demonstrate that these Si-rich glass inclusions are actually magmatic in origin and were trapped inside olivines that crystallized slowly from a magma with a CI, i.e. solar, composition. Their silica-rich compositions are the consequence of the small volumes of inclusions, which inhibit the nucleation of secondary crystalline phase (Ca-poor pyroxene) but allow olivine to continue to crystallize metastably on the walls of the inclusions. We suggest that Si-rich glass inclusions could be the only reliable relicts of what were the first magmas of the solar system, exhibiting a CI, i.e. non-fractionated, composition.

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