ZIRCON U-PB AGE OF THE PARAMO-RICO TONALITE-GRANODIORITE, SANTANDER MASSIF (CORDILLERA-ORIENTAL, COLOMBIA) AND ITS GEOTECTONIC SIGNIFICANCE

We present the first U-Pb, data, which document the existence of early Mesozoic magmatism in the Santander Massif, within the Cordillera Ori ental of Colombia. Zircon fractions separated from a tonalite and a gr anodiorite of the Paramo Rico intrusion yield crystallization ages of 205-210 Ma. Biotite K-Ar ages of other intrusions in this region range from 177 to 210 Ma, overlapping these data, but are reinterpreted as cooling ages after the solidification of the magmatic melts. The Late Triassic/Early Jurassic magmatic activity documented here indicates th at the geotectonic position of the Cordillera Oriental was similar to the present-day position of the South American plate to the Nazca plat e, (i.e., subduction related).