Petrography, Mineralogy, and Metamorphic Evolution of an Eclogite from the Island of Margarita, Venezuela |
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Authors: | MARESCH W V; ABRAHAM K |
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Institution: | Institut für Mineralogie, Ruhr-Universität Bochum 463 Bochum, F.R. Germany |
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Abstract: | The petrography and mineralogy of a coarse-grained eclogitelens from the La Rinconada Group of northeastern Margarita Island,Venezuela, reflect the metamorphic evolution of the rock. Omphacite+ garnet + paragonite + barroisite + epidote + rutile/ilmenite+ quartz + pyrite + apatite represents the stable assemblagemarking the culmination of a single metamorphic episode. Electronmicroprobe analyses of the major minerals indicate an affinitywith Smulikowski's low-temperature ophiolitictype. Schreinemakers relationships among the mineral phasesallow the observed complex reaction relations to be explainedas late-stage depressurization effects. The crystallizationof eclogite instead of amphibole gneiss, as in the chemicallyidentical country rock, must be related to a lower H2O in theaqueous fluid phase attending metamorphism. It is inferred frommineralogical stability data that the culmination assemblagewas stable at approximately 450525 °C and 11.513.5kb load pressure, and that depressurization to less than 5 kboccurred at slightly increasing metamorphic temperatures. |
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