THE METAGABBROS OF THE KASTELHORN AREA (GOTTHARD MASSIF, SWITZERLAND)- THEIR METAMORPHIC HISTORY INFERRED FROM MINERALOGY AND TEXTURE

Mineral assemblages from a large gabbro body in the Kastelhorn area (G otthard massif, central Switzerland) are described. Numerous relic tex tures and occasional relic compositions are found. The textures are co mpared to textures from mafic rocks in the Gotthard massif where relic mineral compositions allow the derivation of the P-T-t path. Typical textures are symplectites and coronites. They show the replacement of primary magmatic assemblages by high-P minerals and subsequent assembl ages of granulite and amphibolite facies. Retrograde overprint at gree nschist facies conditions is generally weak. Relic minerals indicating an eclogite facies event are symplectites with sodic clinopyroxene plagioclase and kyanite inclusions in garnet and plagioclase. The domi nant amphibolite facies mineral assemblage is hornblende + plagioclase + garnet +/- quartz +/- biotite.