METAMORPHISM OF THE GREENSCHISTS AND AMPHIBOLITES FROM THE SANTA MARTA SCHISTS, SIERRA NEVADA DE SANTA MARTA (COLOMBIA): ARCCONTINENT COLLISION BETWEEN THE CARIBBEAN AND THE SOUTH AMERICAN CONTINENT?

The Santa Marta Schists located in the NW Sierra Nevada de Santa Marta segment, on the Colombian Caribbean correspond to a metamorphic sequence of Upper Cretaceous age and volcano-sedimentary protolith with oceanic and continental affinities. Field relations and petrographic features of the amphibolic schists, suggests a sudden increase in the metamorphic grade between Concha and Punta Betin formations and the Rodadero formation. The pressure and temperature calculations using conventional thermobarometry and internally consistent thermodynamic data base for both groups of amphibolic rocks suggests pressure and temperature ranges between 3 - 5 kbar and 300 - 500 degrees C for Concha and Punta Betin and between 7,6 - 9,5 kbar and 565 - 665 degrees C for Rodadero. This suggests that the highest grade rocks overthrusted the lowest grade rocks during syn-metamorphic exhumation. These petrologic relations together with the compositional features of the calcic amphiboles are similar with other rocks formed in a Barrovian medium pressure and temperature baric type, which indicates that the Santa Marta Schists possibly have been formed in a collisional setting, probably related with the Caribbean Arc and South American continental margin collision during Maastrichtian -Paleogene times.