%0 Journal Article
%A Crespo Feo, María Elena
%A Luque Del Villar, Francisco Javier
%A Fernández Rodríguez, Carlos
%A Rodas González, Magdalena
%A Díaz Azpiroz, Manuel
%A Fernández Caliani, J.C.
%A Fernández Barrenechea, José María
%T Significance of graphite occurrences in the Aracena MetamorphicBelt, Iberian Massif
%D 2004
%@ 0016-7568
%U https://hdl.handle.net/20.500.14352/50261
%X The significance of syngenetic and epigenetic graphite occurrences from the Variscan hightemperature/low-pressure Aracena Metamorphic Belt is discussed in the framework of the tectonothermalevolution of this southern zone of the Iberian Massif. Syngenetic graphite is associated withboth low- tomedium-grademetamorphic rocks (LaUmbr´ıa series, Precambrian in age) and high-grade,granulite facies rocks (the Precambrian Fuente del Oro series and a Cambrian calc-silicate series).Epigenetic, fluid-deposited occurrences correspond to overgrowths on existing metamorphic graphitegrains and vein-type mineralization. Two types of graphitized particles with remarkable differences inreflectance, anisotropy and size can be distinguished in the Precambrian metapelites of the La Umbr´ıaseries. Large, >150 μm length, platy crystals with high reflectance and anisotropy are interpreted asdetrital and are considered indirect evidence of an old orogenic cycle prior to the Cadomian Orogeny,during which metamorphism exceeded greenschist facies. The coexistence of two types of particlesexplains the scattering of values of the c parameter of graphite determined by XRD (c=6.72–6.74 A°),and the anomalously high temperatures of the DTA exothermic peak (close to 600 ◦C) of graphitewith respect to that inferred from mineral assemblages in these rocks. The presence of graphite-richquartzites and gneisses within the Fuente del Oro series and the calc-silicate series is evidence ofsedimentation under reducing conditions in a continental shelf. The characteristics of graphite reflectthe high-grade metamorphic conditions attained in the southern area of the Aracena MetamorphicBelt. Pervasive flow of fluids related to a major Variscan extensional event resulted in overgrowthson the pre-existing graphite in the gneisses and quartzites of the calc-silicate series, as evidencedby the heterogeneous isotopic composition of graphite single crystals in these rocks. A later stage ofgraphite precipitation is represented by scarce vein-type occurrences in mafic granulites that documentchannelled flow of fluids.
%~