Petrogenetic implications of chromite-seeded boninite crystallization experiments: Providing a basis for chromite-melt diffusion chronometry in an oxybarometric context
نویسندگان
چکیده
Boninites are rare high magnesium andesites that often contain trace chromites. These chromites precipitate from primitive boninitic melts and thought to be carried the surface in continue crystallize a significant volume of silicate minerals. Such magmatic differentiation drives chromite out equilibrium with residual melt respect both divalent trivalent cation proportions. Diffusion then operates alter toward composition melt. To simulate this process, we have performed internally heated pressure vessel experiments, providing insights into processes chromite-melt re-equilibration through time. While Fe-Mg exchange at temperatures equilibrates tetrahedrally coordinated cations less than 6 hours, equilibration octahedral coordination is slower. Our experimental results show Al concentrations ubiquitously lower, Fe2+/Fe3+ values higher modelled values, indicating there was insufficient time for Fe3+ replacement Cr. Similar observations can made natural compositions extrusive sequence Troodos ophiolite (Cyprus). Based on simple model diffusive equilibration, estimate microphenocrystic up 60 ?m diameter take between days c. 170 years equilibrate under conditions analogous physiochemical state immediately prior eruption. For sequence, implies mafic magmas erupted after extraction mantle disequilibrium textures preserved.
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ژورنال
عنوان ژورنال: Geochimica et Cosmochimica Acta
سال: 2021
ISSN: ['1872-9533', '0016-7037']
DOI: https://doi.org/10.1016/j.gca.2021.01.017