Ordoñez, 2006.Geochronological and Isotopical Review of Devonian Crustal Basement of the Colombian...

Geochronological and isotopical review of pre-Devonian crustal basement of the Colombian Andes Oswaldo Ordo ´ n ˜ ez-Carmona a, * , Jorge Julia ń Restrepo A ´ lvarez a , Ma ´rcio Martins Pimentel b a Universidad Nacional de Colombia, Facultad de Minas, A.A. 1027 Medellı ń-Colombia, Colombia b Instituto de Geocie ˆ ncias, Universidade de Brası ´ lia, CEP: 70910-900 Brasilia, D.F., Brazil Received 1 October 2004; accepted 1 March 2006 Abstract Under the flatlands east of the Andes, the crustal basement is exposed in a few places, composed mainly of the Mitu ´ migmatitic com- plex and the Parguaza granite, whose ages range between 1.78 and 1.45 Ga. Exte nsive outcrop s of high-grade metamorphic rocks are found in several places. Two metamorphisms are dated between 1.2–1.1 and 1.0–0.9 Ga. They are considered blocks that formed during the Grenville oroge ny and have Sm–Nd T DM model ages of 1.87–1.47. The Andaquı ´ terrane is formed mainly by the Garzo ´ n Massif, composed of granulites, migmatites, and granites, and the metamorphic rocks of the Sierra de la Macarena, which are covered by unde- formed Cambrian sediments. It is believed that after the Grenville orogeny, this unit remained attached to the Amazonic Craton. All the other areas grouped in the Chibcha terrane, though they formed during the Grenville orogeny, are believed to have remained either as part of another continental block or dispersed islands to be amalgamated to the Amazonic Craton during the Lower Paleozoic orogeny, which in the Quetame Massif is dated between the Silurian and Devon ian and is named the Quetame orogenic event. 2006 Elsevier Ltd. All rights reserved. Keywords: Colombian Andes; Grenville orogeny; Quetame event 1. Introduction The Colombian Andes are di vi ded into three main branch es, known as the Eas ter n, Centra l, and Wes ter n cordilleras, and include minor orographic systems such as the Sierra Nevada de Santa Marta and the Serranı á de Baudo ´. There is not a complete coincidence between the geology and the orography, because the Colombian Andes are comp osed of allo cht ono us ter ranes accret ed to the Amazonian Craton (Restrepo and Toussaint, 1988; Tous- saint, 1993; Toussaint and Restrepo, 1994, 1996). The East- ern Cordillera, the eastern flank of the Central Cordillera, and parts of the Sierra Nevada de Santa Marta and the Guajira Peninsula constitute the Chibch a terran e, wherea s the western flank of the Central Cordillera and the NW part of the Sierra Nevada de Santa Marta constitute the Tahamı ´ terrane. These two terranes are composed of con- tine ntal crust. The West ern Cor dill era and Serran ı á de Baudo ´ are composed of oceanic crust and are grouped in the Cali ma, Cuna and Gorgona ter ranes, respective ly. The Andaquı ´ terrane lies between the Amazonian Craton and the Chibcha terrane (Fig. 1). The geological history of current Colombian territory can be traced back to the Paleoproterozoic, with the gener- atio n of app rox imat ely 1.8 Ga old roc k uni ts pre sently exposed in easternmost Colombia, along the borders with Brazil and Venezuela. The last important tectonic event was the collision of the Panama-Baudo ´ arc during the late Cenozoic. Aleman and Ramos (2000) provide a br ief review of the geological history of the northern part of the Andes (Ecuador, Colombia, and Venezuela) in the past 2.0 Ga, and Ramos and Aleman (2000) provid e greate r under standin g of the Andea n oroge ny. Dur ing the Pro ter ozoic and Pal eozo ic, evolution was rela ted to a Wilson cyc le, with contin ental collisions at 0895-9811/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsames.2006.07.005 * Corresponding author. E-mail address : [email protected] (O. Ordo ´ n ˜ ez-Carmona). www.elsevier.com/locate/jsames Journal of South American Earth Sciences 21 (2006) 372–382

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