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Modelos orogénicos de tectónica de placas en los Andes Colombianos

1976; National University of Colombia; Issue: 1 Linguagem: Espanhol

2357-3740

Jean François Toussaint, Jorge Julián Restrepo,

History and Politics in Latin America

espanolLos Andes Colombianos son el resultado de la superposicion de varias orogenias que corresponden a distintos tipos de cadena. En la Cordillera Oriental una cadena caledoniana se desarrolla encima del zocalo precambrico y no produce acrecimiento continental; algunas de sus caracteristicas la aproximan a un tipo de cadena andina. En la Cordillera Central y en la Sierra Nevada un intenso metamorfismo Abukuma acompanado de pequenos plutones indica una fuerte orogenia herciniana. Esta cadena, que es en parte suprasimica y de tipo alpino, se formo aparentemente como consecuencia de la colision entre Centroamerica septentrional y Suramerica. Estas dos placas se separaron durante el Triasico debido a la actividad de un rift que genero corteza oceanica entre ellas. Durante el Triasico-Jurasico en las margenes del Valle del Rio Magdalena se formo un cinturon magmatico acompanado por un graben tensional supracratonico ; ambos fenomenos parecen estar asociados a una subduccion activa localizada al occidente de la Cordillera Central. Durante este lapso de tiempo los Andes Colombianos tienen caracteristicas tipicamente andinas. Recientes determinaciones radiometricas han permitido conocer mejor la compleja historia del occidente durante el Cretaceo. Una corteza oceanica, datada en 131 m.a., se genero en un rift localizado a corta distancia del continente. A finales del Albiano parte de esta corteza fue obducida sobre el basamento de la Cordillera Central. Esta obduccion produjo un metamorfismo de presion media datado entre 110 m.a. y 100 m.a. Durante el Cretaceo tardio una subduccion situada al occidente de la Cordillera Occidental permitio la formacion de un cinturon tonalitico en la parte septentrional de la Cordillera Central y de un arco basico en la Cordillera Occidental. Este arco parece estar acompanado de un metamorfismo de muy bajo grado. Durante el Cretaceo la cadena tiene caracteristicas mixtas, ya que la incorporacion de material oceanico, sea por obduccion, sea por acrecimiento, es una caracteristica alpina, mientras que el magmatismo en la Cordillera Occidental es de tipo arco, que pasa lateralmente en la Cordillera Central a uno de tipo andino. Fallas de rumbo, tales como las de Cauca-Romeral y Palestina, se producen a finales del Cretaceo o a principios del Terciario. Finalmente, durante el Cenozoico la Cordillera Occidental evoluciona como arco suprasimico en proceso de continentalizacion, mientras que la Cordillera Oriental se comporta como una cadena intracontinental. EnglishThe present Andes of Colombia are a complex mountain chain formed by the superposition of several orogenies. To understand this final result it is necessary to separate in space and time each orogenic event, determining when and were it took place and what orogenic model it followed. In the Eastern Cordillera a Caledonian chain was formed over Precambrian basement and without continental accretion; most of the characteristics belong to an Andean type of chain. In the Central Cordillera and the Sierra Nevada strong metamorphism and small plutons were formed during a late Hercynian orogeny. This chain, which is partially suprasimic and of Alpine type, was probably formed by the collision of northern Mesoamerica and northwestern South America. The two plates were separated during the Triassic by an active rift that generated oceanic crust between them. During the Late Triassic and Jurassic a magmatic belt and a supracratonic graben were formed in the margins of the Magdalena Valley.Both features seem to be related to an active subduction zone located to the west of the Central Cordillera. During this event the modell is typically Andean. The Cretaceous history is very complex, but the major events have been dated by some recent radiometric ages. An oceanic crust was generated in an active rift located to the west of the Central Cordillera.This crust, dated at 131 m.y., was obducted over the continental crust of the Central Cordillera at the end of the Early Cretaceous. The obduction produced dynamic effects, especially a Barrovian metamorphism dated at 110 and 100 m.y. During the Late Cretaceous a new subduction zone was formed at the western margin of the Western Cordillera, trapping Lower Cretaceous oceanic crust that was since then accreted to the continent.The associated magmatism corresponds to tonalitic plutonism in the Central Cordillera and to a basic volcanic arc (92 m.y.) in the Western Cordillera; the inmature arc was affected by a very-low grade metamorphism. The Cretaceous evolution corresponds to several orogenic models, and in this sense it is a mixed or compound type of orogeny. The incorporation of the oceanic crust -by obduction and by accretion- and the associated metamorphism correspond to an Alpine model, while the basic magmatism of the Western Cordillera corresponds to a suprasimic volcanic arc that passes laterally to an Andean type of magmatism in the Central Cordillera. Strike - fault systems, such as the Cauca - Romeral and Palestina, were formed at the close of the Cretaceous or the beginning of the Tertiary. During the Tertiary a new subduction zone, probably located at the present continental margin, produced intermediate plutonism in the Western Cordillera. This plutonism is the beginning of the cratonisation of this chain and corresponds to a more mature volcanic arc. In the Eastern Cordillera the sediments deposited since the Late Paleozoic were deformed and uplifted according to an intracratonic model.