THE CORDIERITE-ORTHOAMPHIBOLE ROCKS OF THE VARISCAN DOME OF GAVARNIE-GEDRE-HEAS: THE GEDRITE OF GEDRE (HAUTES PYRENEES, FRANCE)

摘要

The low-P/high-T Variscan metamorphic dome of Gavarnie-Gedre-Heas, Central Pyrenees, harbors a small (1 m(3)) but special cordierite and orthoamphibole-bearing enclave embedded within an anatectic granite. Compared to other cordierite-orthoamphibole occurrences described in the literature, the enclave shows singular characteristics: (1) its mineral composition is unique with cordierite (Crd)+gedrite (Ged) + biotitess (Bt) +staurolite (St) + garnet (Grt) + spinel (Spl) + corundum (Crn) + ilmenite (Ilm) and sulfides (Sulf), but lacking quartz (Qtz), plagioclase (Pl), and aluminosilicate minerals; and (2) its chemical composition, with low SiO2, high Al2O3, K2O, and TiO2 and high Fe2O3T/MgO. The Crd-Oam-bearing rocks also occur as layers in stromatic migmatites that show a mineral composition (Bt+Crd+Ged+Pl+Qtz+Ilm+Grt 6 St) and a chemical composition more akin to other described occurrences.