RESUMEN:En el Complejo Guarguaraz, ubicado en la Cordillera Frontal de Argentina (latitud 33,3°S), se encuentran lentes de serpentinita, metabasitas y metasedimentitas de granate. De acuerdo con autores previos, el evento metamorfico asociado ha sido asignado a la formacion de un complejo de prisma de acrecion en el Devonico. Esta hipotesis ha sido evaluada con el estudio metamorfico de una metapelita del complejo. El granate en la roca muestra una zonacion prograda bien desarrollada. Micas blancas potasicas, con contenidos de Si entre 3,38 (nucleo) y 3,12 (borde) por formula unitaria, biotita, cuarzo y plagioclasa, coexisten con granate. Sobre la base de seudosecciones de presion y temperatura y equilibrios anhidros, hemos estimado la trayectoria P-T para la metapelita estudiada. El nucleo del granate se formo en condiciones cercanas a los 8 kbar y 470-500°C. Despues de un enterramiento isotermal hasta 45 km (13,5 kbar), condiciones en las que la fengita rica en Si se formo, aumento la temperatura y ocurrio la exhumacion y una etapa de sobreimposicion metamorfica a 8 kbar y 560°C. Esta trayectoria P-T no es compatible con el desarrollo de un complejo de prisma de acrecion. Es mas probable que las condiciones de alta presion fueran alcanzadas durante el engrosamiento de la corteza continental cuando el hipotetico terreno de Chilenia colisiono con el margen continental de Gondwana en el Devonico.ABSTRACT:In the Guarguaraz Complex of the Argentine Frontal Cordillera (latitude 33.3°S) serpentinite lenses, metabasites, and garnet-bearing metasedimentary rocks occur. The corresponding Devonian metamorphic event was assigned to the formation of an accretionary wedge by previous authors. We have tested this hypothesis by investigating the metamorphic evolution of a pelite from this complex. Garnet in this rock shows a well evolved prograde zoning. Potassic white mica with Si contents between 3.38 (core) and 3.12 (rim) per formula unit, biotite, quartz and plagioclase, which have formed late blasts at the expense of amphibole, coexist with this phase. On the basis of P-T pseudosections and water-absent equilibria, we have estimated the subsequent P-T path for the studied metapelite. The garnet core formed at about 8 kbar and 470-500°C. After nearly isothermal burial to 45 km (13.5 kbar) where Si-rich phengites grew, temperatures increased followed by exhumation and an overprint stage at 8 kbar and 565°C. This P-T path is not compatible with the idea of an accretionary wedge complex. It is more likely that the high-pressure conditions were attained by thickening of continental crust when the hypothetical Chilenia terrane collided with the continental margin of western Gondwana in Devonian times.In the Guarguaraz Complex of the Argentine Frontal Cordillera (latitude 33.3°S) serpentinite lenses, metabasites, and garnet-bearing metasedimentary rocks occur. The corresponding Devonian metamorphic event was assigned to the formation of an accretionary wedge by previous authors. We have tested this hypothesis by investigating the metamorphic evolution of a pelite from this complex. Garnet in this rock shows a well evolved prograde zoning. Potassic white mica with Si contents between 3.38 (core) and 3.12 (rim) per formula unit, biotite, quartz and plagioclase, which have formed late blasts at the expense of amphibole, coexist with this phase. On the basis of P-T pseudosections and water-absent equilibria, we have estimated the subsequent P-T path for the studied metapelite. The garnet core formed at about 8 kbar and 470-500°C. After nearly isothermal burial to 45 km (13.5 kbar) where Si-rich phengites grew, temperatures increased followed by exhumation and an overprint stage at 8 kbar and 565°C. This P-T path is not compatible with the idea of an accretionary wedge complex. It is more likely that the high-pressure conditions were attained by thickening of continental crust when the hypothetical Chilenia terrane collided with the continental margin of western Gondwana in Devonian times.