Geochronological and isotopical review of pre-Devonian crustal basement of the Colombian Andes

摘要

Under the flatlands east of the Andes, the crustal basement is exposed in a few places, composed mainly of the MM migmatitic complex and the Parguaza granite, whose ages range between 1.78 and 1.45 Ga. Extensive outcrops 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 orogeny and have Sm-Nd T_(DM) model ages of 1.87-1.47. The Andaqui terrane is formed mainly by the Garzon 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 Devonian and is named the Quetame orogenic event.