Tectono-metamorphic evolution of the Silgara Formation metamorphic rocks in the southwestern Santander Massif, Colombian Andes

The Lower Paleozoic Silgara Formation in the southwestern Santander Massif was affected by Caledonian regional metamorphism, which created a sequence of metamorphic zones (sillimanite, staurolite, garnet, and biotite). The regional metamorphic grade of the Silgara Formation decreases southwestward from the sillimanite zone to the biotite zone. Metamorphism has occurred under low to high temperature and medium pressure conditions (Barrovian-type metamorphism) and reflects the high heat flow in this part of the Santander Massif. P-T conditions (495-518 degreesC and 4.4-5.5 kbar garnet zone; 590-612 degreesC and 6.6-7.5 kbar staurolite zone; 660-700 degreesC and 5.5-7.2 kbar sillimanite zone) were estimated by different thermometers and barometers. The Silgara Formation shows evidence of a complex metamorphic evolution characterized by crustal thickening during heating and a regional retrograde metamorphism after the peak metamorphic temperature. (C) 2003 Elsevier Science Ltd. All rights reserved.