P-T path of felsic granulite from south-east Corsica (France) and implications for geodynamic setting

Cruciani G;Franceschelli M;Massonne H-J;Musumeci G

2019-01-01

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Abstract

The Solenzara-Fautea unit is made up of Variscan rocks outcropping between the villages of Fautea and Solenzara in SE Corsica (Faure et al., 2014). The unit consists of migmatites and garnet-kyanite granulitic gneiss with pyroxenite and pyrigarnite boudins (Rossi & Faure, 2012). To better understand the metamorphic evolution of this series we studied a gneiss exposed at the seashore south of the village of Tarcu. This foliated leucocratic rock, characterized by the alternation of quartzofeldspathic and biotite-rich layers, consists of quartz, mesoperthitic plagioclase, perthitic K-feldspar, garnet, biotite, kyanite, and subordinate muscovite and chlorite. Garnet occurs as millimetre-sized porphyroblasts or as small crystals in the matrix or included in kyanite. The porphyroblasts are rich in quartz, plagioclase, apatite and rutile inclusions and show an asymmetric compositional zoning with a Ca-rich core surrounded by an Fe-rich rim. The P–T path of the gneiss was reconstructed on the basis of garnet compositional zoning and isochemical phase diagrams. The garnet core formed at ca. 1.6 GPa and 700-750°C and, thus, at clearly lower temperatures than previously reported. These peak P-T conditions were followed by an almost isothermal decompression to pressure conditions of 0.8 GPa at ca. 700°C. The inferred clockwise P-T path is in agreement with estimations obtained with the Zr-in-rutile thermometer (730-740°C). The P-T conditions derived from the garnet rim (650-750°C; 0.7-0.9 GPa) are similar to those reported for paragneiss of the Porto Vecchio unit (Giacomini et al., 2008), 40 km south of the Fautea-Solenzara unit. The P-T path of the garnet-kyanite granulitic gneiss from Tarcu area is discussed in the framework of the Variscan Corsica geodynamic setting. Faure M., Rossi P., Gaché J., Melleton J., Frei D., Li X. & Lin W. (2014) - Variscan orogeny in Corsica: new structural and geochronological insights, and its place in the Variscan geodynamic frameworkInt. J. Earth Sci., 103,1533–1551. Giacomini F., Dallai L., Carminati E., Tiepolo M. & Ghezzo C. (2008) - Exhumation of a Variscan orogenic complex: insights into the composite granulitic–amphibolitic metamorphic basement of south-east Corsica (France). J. Metam. Geol., 26, 403–436. Rossi P. & Faure M. (2012) - The Variscan Corsica. Field trip guide. Géol. France, 1, 11-23.