P–T–t conditions of high-grade metamorphic rocks of the Garzon Massif, Andean basement, SE Colombia Diana Marı ´a Jime ´nez Mejı ´a a, * , Caetano Juliani b , Umberto G. Cordani b a INGEOMINAS Bogota ´ , Diag. 53 No. 34-53, A.A. 4865, Bogota ´ , Colombia b Instituto de Geocie ˆncias, Universidade de Sa ˜o Paulo, R. Lago, 562, CEP 05508-080, Sa ˜o Paulo, SP, Brazil Received 1 October 2004; accepted 1 February 2006 Abstract The metamorphic evolution of the Garzo ´ n Massif, Colombia, is established on the basis of the textural, goethermobarometric, and geochronological relationships of the metamorphic minerals. The geothermobarometric data define a clockwise, nearly isothermal decompression path (ITD) for rocks from Las Margaritas migmatites, constrained by four P–T areas: 780–826 °C and 6.3–8.0 kbar, 760–820 °C and 8.0–8.8 kbar, 680–755 °C and 6.6–9.0 kbar, and 630 °C and 4 kbar. For the a garnet-bearing charnockitic gneiss from the Vergel granulites, the path is counterclockwise, constrained by geothermobarometric data of 5.3–6.2 kbar and 700–780 °C and 6.2– 7.2 kbar and 685–740 °C. The clockwise ITD path represents a loop followed by the orogen during the transitional granulite–amphibolite metamorphic conditions, probably associated with a subduction process followed by a collisional tectonic event. This subduction frame- work produced continental crust thickening between 1148 and 1034 Ma and later collision with another continental block approximately 1000 Ma ago. The orogenic exhumation occurred with moderate uplift rate. The counterclockwise trajectory and two metamorphic events suggest a vertical displacement between the Vergel granulites and Las Margaritas migmatites units, because there is no isotopic difference that indicates the existence of different terranes. The data confirm that the metamorphic evolution for this domain was more dynamic than previously believed and includes: (1) metamorphic processes with the generation of new crust with a possible mixture of old material and (2) metamorphic recycling of continental crust. These geological processes characterize a complex Mesoproterozoic orogen- ic event that shares certain features with the Grenvillian basement rocks participating in the formation of Rodinia. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Colombia; Geothermobarometry; Granulites; Grenvillian rocks; Andes Resumen La historia presio ´ n–temperatura–tiempo (P–T–t) de las metamorfitas del Macizo de Garzo ´n – Colombia, fue establecida con base en las relaciones texturales, termobarome ´tricas y geocronolo ´ gicas de los minerales metamo ´ rficos. Los datos P–T–t definen para las rocas de las Migmatitas de Las Margaritas una trayectoria horaria de descompresio ´ n cercanamente isotermal (ITD), definida por cuatro zonas en el grafico P–T: 780–826 °C y 6.3–8.0 kbar, 751–778 °C y 7.7–8.1 kbar, y 688–752 °C y 6.8–7.9 kbar, y 630 °C y 4 kbar . En contraste, para las rocas de las Granulitas del Vergel el camino es anti-horario, definido por datos geotermobarome ´tricos de 5.3–6.2 kbar y 700–780 °C, y 6.2–7.2 kbar y 685–740 °C. La trayectoria horaria (ITD) representa un camino seguido por el oro ´ geno durante las condiciones meta- mo ´ rficas en transicio ´ n anfibolita–granulita, probablemente asociado a un proceso de subduccio ´ n. Este ambiente de subduccio ´ n produce inicialmente, al interior del oro ´ geno, una corteza continental engrosada entre 1148–1034 Ma, y posteriormente una colisio ´n con otra masa continental a 1000 Ma aproximadamente. La exhumacio ´n del oro ´ geno estuvo acompan ˜ ada por tectonismo con moderadas tasas de levantamiento. La trayectoria anti-horaria y los dos eventos metamo ´ rficos permiten sugerir movimiento vertical entre las unidades Granulitas del Vergel y Migmatitas de Las Margaritas, en vez de la existencia de terrenos diferentes, ya que no hay diferencias isoto ´ picas. Los datos obtenidos confirman que la evolucio ´ n metamo ´ rfica de este dominio cortical fue un proceso dina ´ mico que incluye los eventos de 0895-9811/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsames.2006.07.001 * Corresponding author. Tel.: +57 1 2200273; fax: +57 1 2223764. E-mail address: djimenez@ingeominas.gov.co (D.M. Jime ´nez Mejı ´a). www.elsevier.com/locate/jsames Journal of South American Earth Sciences 21 (2006) 322–336