TEM observations of several spinel-garnet assemblies: toward the rheology of the transition zone |
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| Authors: | Jannick Ingrin Michel Madon |
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| Institution: | Laboratoire de Géophysique et Géodynamique Interne, B timent 510, UniversitéParis Sud, 91405 Orsay;Laboratoire de Physique et Mécanique des Géomatériaux, Universitéde Marne-la-Vallée, 93166 Noisy-le-Grand Cedex, France |
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| Abstract: | In order to better identify the mineral phase which controls the rheology of the transition zone (between 410 and 660 km depth) transmission electron microscopy observations were made on several coexisting spinel-garnet assemblies: alkremite xenolith; pyrope-rich – MgO:1.1Al2O3 spinel assembly deformed at 1173K, 800 MPa in a Griggs apparatus; (Mg,Fe)3(Al,Mg,Si)2Si3O12 majorite – (Mg,Fe)2SiO4 spinel assembly synthesized in a laser heated diamond anvil cell. It was found that garnet crystals systematically remain undeformed while spinel crystals are plastically deformed. These results are in accord with the assumption that the rheology of majorite is stronger than the rheology of spinel, in the conditions of the transition zone. |
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