Metamorphism on Chromite Ores from the Dobromirtsi Ultramafic Massif, Rhodope Mountains (SE Bulgaria)
González-Jiménez, J. M. (Universidad de Granada. Departamento de Mineralogía y Petrología)
Kerestedjian, T. (Bulgarian Academy of Sciences. Geological Institute)
Proenza, J. A. (Universitat de Barcelona. Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals)
Gervilla, F. (Universidad de Granada. Departamento de Mineralogía y Petrología)

Date:	2009
Abstract:	Podiform chromitite bodies occur in highly serpentinized peridotites at Dobromirtsi Ultramafic Massif (Rhodope Mountains, southeastern Bulgaria). The ultramafic body is believed to represent a fragment of Palaeozoic ophiolite mantle. The ophiolite sequence is associated with greenschist - lower-temperature amphibolite facies metamorphosed rocks (biotitic gneisses hosting amphibolite). This association suggests that peridotites, chromitites and metamorphic rocks underwent a common metamorphic evolution. Chromitites at Dobromirtsi have been strongly altered. Their degree of alteration depends on the chromite/silicate ratio and to a lesser extent, on the size of chromitite bodies. Alteration is recorded in individual chromite grains in the form of optical and chemical zoning. Core to rim chemical trends are expressed by MgO- and Al2O3- impoverishment, mainly compensated by FeO and/or Fe2O3 increases. Such chemical variations correspond with three main alteration events. The first one was associated with ocean-floor metamorphism and was characterized by a lizardite replacement of olivine and the absence of chromite alteration. The second event took place during greenchist facies metamorphism. During this event, MgO- and SiO2-rich fluids (derived from low temperatura serpentinization of olivine and pyroxenes) reacted with chromite to form chlorite; as a consequence, chromite became altered to a FeO- and Cr2O3-rich, Al2O3-poor chromite. The third event, mainly developed during lower temperature amphibolite facies metamorphism, caused the replacement of the primary and previously altered chromite by Fe2O3-rich chromite (ferritchromite).
Rights:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan aquestes es distribueixin sota la mateixa llicència que regula l'obra original i es reconegui l'autoria de l'obra original.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	Ophiolite ; Chromite ; Metamorphism ; Dobromirtsi Ultramafic Massif ; Bulgaria
Published in:	Geologica acta, Vol. 7, Núm. 4 (Desembre 2009) , p. 413-429, ISSN 1696-5728

Adreça alternativa: https://raco.cat/index.php/GeologicaActa/article/view/140184
Adreça alternativa: https://revistes.ub.edu/index.php/GEOACTA/article/view/104.000001447
DOI: 10.1344/104.000001447

17 p, 1.4 MB

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