Discrimination of tectonic provinces using zircon U-Pb ages from bedrock and detrital samples in the northern Andes

Abstract

The northern Andes of southern Colombia contain a rich geologic history recorded by Proterozoic to Cenozoic metamorphic, igneous, and sedimentary rocks. The region plays a pivotal role in understanding the evolution of topography in northwestern South America and the development of large river systems, such as the Amazon, Orinoco, and Magdalena rivers. However, understanding of the basement framework has been hindered by challenging access, security concerns, tropical climate, and outcrop scarcity. Further, an insufficient geochronologic characterization of Andean basement complicates provenance interpretations of adjacent basins and restricts understanding of the paleogeographic evolution of southern Colombia. To address these issues, this paper presents a zircon U-Pb geochronological dataset derived for 24 bedrock samples and 19 modern river samples. The zircon U-Pb results reveal that the Eastern Cordillera of southern Colombia is underlain by basement rocks that originated in various tectonic events since ca. 1.5 Ga, including the accretion of discrete terranes. The oldest rocks, found in the Garzon Massif, are high-grade metamorphic rocks with contrasting Proterozoic protolith crystallization ages. Whereas the SW part of the massif formed during the Putumayo Orogeny (ca. 1.2−0.9 Ga), we report orthogneisses for the NE segment with protoliths formed at ca. 1.5 Ga, representing the NW continuation of the Rio Negro Jurena province of the Amazonian Craton. In contrast, crystalline rocks of the Central Cordillera primarily consist of Permian−Triassic (ca. 270−250 Ma) and Jurassic−Cretaceous (ca. 180−130 Ma) igneous rocks formed in a magmatic arc. In southernmost Colombia, the Putumayo Mountains mainly consist of Jurassic−Cretaceous (180−130 Ma) plutonic and volcanic rocks. Furthermore, we analyzed the heavy mineral abundances in modern river sands in southern Colombia (spanning 1°N−5°N) and found that key minerals such as garnet and epidote can be utilized to trace high-grade metamorphic and igneous lithologies, respectively, in the river catchments. The differentiation of basement ages for separate tectonic provinces, combined with heavy mineral abundances in modern sands, can serve as unique fingerprints in provenance analyses to trace the topographic and exhumational evolution of different Andean regions through time.