Facing geological mapping at low-latitude volcanoes: The Doña Juana Volcanic Complex study-case, SW-Colombia

Abstract

We present the Doña Juana Volcanic Complex (DJVC) geological map, stratigraphy, Ar/Ar-and-C14 geochronology resulting from a pilot-mapping project in Colombia, as a study-case for the application of modern, international volcano geology techniques in low-latitude environments. Lithostratigraphy and lithofacies analysis (for description of rock bodies and mapping), lithosomes (for the definition of eruptive centres) and unconformity-bounded units (for stratigraphic correlation), as well as new geochronological data and the interpretation of eruption units were successfully integrated. The geological mapping and stratigraphic analysis provided an effective representation of the volcanic edifices/vents that make up the DJVC, so that we could reconstruct the geological evolution from the time and spatial distribution of the corresponding volcanic products and the range of lithofacies associations. The geological database and the forthcoming interpretation in terms of eruption behaviour establish the basis for realistic long-term hazard assessment.The DJVC is a calc-alkaline dacitic volcanic complex within the Central Cordillera of Colombia, which started its activity about 1125.4 ± 4.4 ka ago. It comprises three spatially overlapping edifices and three adventive cones, which unconformably overlay Lower Cretaceous metasedimentary and metavolcanic rocks of oceanic origin. Each of the three overlapping edifices is truncated at the summit by a volcano-tectonic depression, without identifiable caldera-forming products. Two of these volcano-tectonic features display important proximal unconformities and, together with their correlative disconformities and paleosols, indicate significant quiescences of volcanic activity. The Holocene record has been mostly characterized by the emission of three lava-dome fields infilling the youngest volcano-tectonic depression and interrupting the corresponding unconformity. These lava domes have recurrently collapsed to originate block-and-ash flows followed by vulcanian explosions producing pyroclastic density currents and lahars. The corresponding eruptive products have drained along the present river basins to the NE and SW of DJVC, forming depositional terraces currently populated by nearly 49,000 rural and urban inhabitants.