El Escondido, a newly identified silicic Quaternary volcano in the NE region of the northern volcanic segment (Central Cordillera of Colombia)

Abstract

El Escondido (1650m.a.s.l.) is a silicic Quaternary volcano recently identified on the Central Cordillera of Colombian Andes. It is located about 50km NE from the northern segment of active volcanoes. It has been recognized as a polygenetic pyroclastic-dome ring complex structure, whose eruptive products derived from a crater-like semi-circular depression of ~1.7km in diameter. This crater formed at the contact of the Granitic Florencia Stock (54.9±1.8my) with the Paleozoic metamorphic basement, and at the intersection of the NNESSW trending Palestina fault system with an EW trending fault. The preserved volcano morphology and the volcanic succession associated with it were defined as the El Escondido volcanic center. The eruptive products are alternating silicic (mostly dacitic) pyroclastic density current deposits, pumice fall deposits and ballistic projectiles, which suggest high explosiveness. Two 14C radiogenic dates obtained on carbonized wood fragments of the middle part of the eruptive sequence displayed ages of 36,030±380 BP and 33,550±280 BP suggesting two major eruptive episodes of the volcano about 2500years apart. The latest eruptive activity is inferred to be the emplacement of lava domes to the south of the crater-like structure, which are responsible for the partial destruction of the pyroclastic ring in that sector. The products emitted by El Escondido correspond to medium K andesites to dacites of the calc-alkaline series and petrographically to amphibolic andesites. Towards the western and eastern sector of the volcano, there are chlorinated thermal waters with temperatures up to 45°C. The first monitoring of the volcanic activity, carried out by the Colombian Geological Survey (CGS) through the Volcanological and Seismological Observatory of Manizales (VSOM), has not detected so far unusual volcano-seismic activity. The previously unreported El Escondido volcano represents one of the northernmost occurrence of Quaternary volcanism in the whole Andean cordillera, thus, its study may have wide implications regarding the geodynamics of the region and subduction zone, the correct assessment of geologic hazards and the identification of natural resources, like geothermal reservoirs and mineral deposits of economic interest.