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

Faure, F. ; Tissandier, L. ; Florentin, L. ; Devineau, K., GCA

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

Faure, F. ; Tissandier, L. ; Florentin, L. ; Devineau, K.

Geochimica et Cosmochimica Acta, 2017, 204, 19-31

Abstract :

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 silicarich 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.

Voir en ligne : http://dx.doi.org/10.1016/j.gca.201...



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publié vendredi 17 février 2017