MEDIUM-PRESSURE METAMORPHISM IN THE CENTRAL SANTANDER MASSIF, EASTERN CORDILLERA, COLOMBIAN ANDES

ABSTRACT The Central Santander Massif exposes its metamorphic basement, which mainly consists of medium- to high-grade pelitic schists, paragneisses, migmatites and orthogneisses. For delineating its metamorphic evolution, we have examinated mineral assemblages, metamorphic reactions and P-T conditions of metamorphic rocks of this region. Metamorphism has occurred under conditions of high-temperature and medium-pressure (Barrovian type metamorphism), and three metamorphic zones were developed: staurolite-kyanite, sillimanite and migmatite zones. Pressure and temperatura conditions, estimated by TWQ program, are in the range of 5.0-9.5 kbar and 630-727oC. The P-T path of the metamorphic units is clockwise suggesting a collision model for this region of the Colombian Andes. Keywords : Metamorphism; Santander Massif; Barrovian type; P-T path; collision METAMORFISMO DE PRESION INTERMEDIA EN LA REGION CENTRAL DEL MACIZO DE SANTANDER, CORDILLERA ORIENTAL, ANDES COLOMBIANOS RESUMEN La region central del Macizo de Santander expone su basamento metamorfico, el cual consiste de esquistos peliticos, paraneises, migmatitas y ortoneises de medio a alto grado. Para delinear su evolucion metamorfica, hemos examinado las paragenesis minerales, reacciones metamorficas y condiciones de P-T de las rocas metamorficas de esta region. El metamorfismo ocurrio bajo condiciones de alta temperatura y presion intermedia (metamorfismo tipo Barroviano), con el desarrollo de tres zonas metamorficas: estaurolita-cianita, silimanita y migmatita. Las condiciones de presion y temperatura, estimadas mediante el programa TWQ, estan en el rango de 5.0-9.5 kbar y 630-727oC. La trayectoria de PT de las unidades metamorficas es en sentido horario sugiriendo un modelo de colision para esta region de los Andes Colombianos. Palabras claves : Metamorfismo; Macizo de Santander; tipo Barroviano; trayectoria de P-T; colision.