NEOGENE MAGMATIC RECORD OF THE SOUTHERN COLOMBIAN ANDES: TECTONIC AND MOUNTAIN BUILDING IMPLICATIONS

Several Cenozoic Andean Continental arcs are characterized by ≥100 Km frontal arc migration that has been related to different mechanisms such as changes in slab dipping, subduction erosion, and crustal thickening among others. In contrast, the southern Colombian Andes are characterized by restricted arc migration (<100 km) during the Neogene that is also accompanied by arc and retro-arc deformation.

Some questions remain to be answered in this Neogene Colombian arc, which most have major implications for the tectonic evolution of continental arcs and this segment of the Andean margin. Was it a migrating or a stationary arc? Was it continuous magmatism or may it include some hiatus? How does the arc width may change through time? What is the relation between magmatism, deformation, and exhumation?.

A review of published and new field, stratigraphic, geochronological, and compositional data, from the southern segment of the Colombian arc (south of 4°N) suggest that arc magmatism was active between 23 Ma and recent times. The magmatic arc started in the Western Cordillera at ca 23 Ma at ~235 km of the current trench, as suggested by small plutonic bodies representing the frontal arc. Between 15 and 9 Ma, the arc is located ~30 km eastward from the Lower Miocene arc, whereas the 8 to 3 Ma is ~20-35 km to the east of the Middle Miocene arc, while the recent magmatism extends again to the west (~40km), covering the older Early Miocene arc. In contrast with the older arc that characterized by a more restricted occurrence, arc magmatism younger than 8 Ma and including the modern arc is broader with widths between 40-50 km.

This zone has a complex spatio/temporal evolution overlap with several deformation and exhumation phases in the arc and retro-arc areas, which suggest a more intricate scenario, in which arc magmatism plays a fundamental role in the Northern Andean orogenic growth.