SUMMARY
The Orthogneiss unit in the Santander Massif, Northern Colombian Andes, mainly consists of quartzfeldspathic, pelitic and minor mafic orthogneisses and amphibolites. Petrographic, geochemical and geochronological studies carried out on orthogneisses from the Silos-Babega belt, indicate that they are granodioritic and granitic in composition with protolith formed by crustal melting in an active continental magmatic arc. They were syntectonically emplaced in the Silgara Schists unit. Metamorphic peak of the Orthogneiss unit reach amphibolite facies conditions in the range of 4.3-10 kbar in pressure and 540-690 °C in temperature. Zircon U-Pb LA-ICP-MS ages of 471±11 and 479±10 Ma were obtained and these ages are similar to those known for the Orthogneiss unit in the central and the eastern Santander Massif and confirm the continuity to the north of the Andean protomargin as a result of the Famatinian orogeny.