Emplacement of Paleocene-Eocene magmatism under transtensional regime and its evolution to a dynamic equilibrium on the western edge of Colombia

Abstract

The Cretaceous and Paleogene magmatic arcs of the Central and Western Cordilleras of Colombia have been attributed to the evolution of a subduction system in the Colombian Pacific coast. In this work the distribution and crystallization ages of plutons emplaced between 60 Ma and 53 Ma in the Central and Western Cordilleras are analyzed. From 53 Ma the magmatic arc migrates towards the west of Colombia, installing magmas in a plate edge transitional crust. The crystallization ages analyzed in this work suggest that, within the study area, the plutonic belt is continuous throughout the Western Cordillera. From 40±5 Ma to 26 Ma there was a significant reduction in the convergence velocity of the Farallon plate; as it decreases, also the tectonic loading diminishes resulting in a process of regional stress relaxation. The process of relaxation of the regional stress also occurred in the intra-continental environments producing peneplanization process in the topographic highs of northern Colombia, the reactivation of the piedmont with westwards progradation of sedimentation and the development of a middle- to late-Eocene regional unconformity. In continental shelf environments, the relaxation of the tectonic stress is evidenced by the distribution of reef limestone sequences throughout the Colombian Pacific margin and the Caribbean of Colombia, Ecuador, Panama and Costa Rica, and by a magmatic gap from 33 Ma to 26 Ma. The Paleocene-Eocene magmatic event distributed in the Central and Western Cordilleras took place under a transtensional regime, with the maximum horizontal compressive stress (σ1) oriented SW-NE, product of the oblique convergence between the Farallon and South American plates.