GeologyGaleras Volcanic Complex Evolution
Detailed field studies as well as Carbon 14 dating have established a strong stratigraphic and chronologic framework at Galeras. This framework defines six separate stages of evolution at the Galeras volcanic complex, plus the current Galeras volcano. Volcanic Evolution: (Oldest to Youngest)
VIew figure 13 for geologic map of Galeras volcano. Chronological information obtained from: Calvache, Cortes (1997). Figure 13: 1 = Galeras Range; 2 = Urcinima stage; 3 = Jenoy stage; 4 = La Guaca cinder cone; 5 = Coba Negra stage 6 = Pamba stage; 7 = Cariaco stage; 8 = youngest avalanche deposit: 9 = middle avalanche deposit; IO = oldest avalanche deposit; 11 = alluvial deposits: 12 = moraine deposit; 13 = geological contact: 14 = inferred geological contact; 15 = caldera; 16 = amphitheater. Modified from Calvache, Cortes (1997).
Geochemistry and Petrology
During the last million years, the Galeras Volcanic Complex has erupted lavas from basaltic andesites to Dacite. However the chemical composition of the erupted volcanic materials has stayed relatively constant, and is characterized by calc-alkaline, high-silica, medium potassic andesites. A variation between basaltic andestite to dacites is present in various stages, but largely the composition is constant. The major exception to this is the La Guaca cone, which is more alkaline than sub alkaline (Fig. 15). Trace element and rare earth concentrations are consistent with the theory that subducted sediments along the western boundary of South America involved in the generation of the magma at Galeras (Calveche, Williams, 1997). Figure 15: Classification of alkalic and sub-alkalic volcanic rocks for whole rock analyses of the Galeras Volcanic Complex. Retrieved from: Calveche, Williams (1997)
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Figure 12: Generalized geologic map of Colombia. Galeras Volcano is located within the Cretaceous-Tertiary rocks in the Southwestern portion of the map. Retrieved from: http://geology.about.com /od/othernationgeomaps/ss/South-America-Geologic-Maps_5.htm
Stratigraphy and Volcanic DepositsHistoric deposits are largely alternating block and ash flows deposits and lava flow deposits. The variation is believed to be a differnence in eruptive style, indicating a change from explosive to effusive (Calveche, Cortes, 1997). Figure 14 below represents this alternating nature.
Figure 14: Stratigraphic column showing age dates in relation to stratigraphy. Dark layers indicate block and ash flow deposits while lighter, horizontally lined, layers indicate lava flows. Modified from Calcache, Cortes (1997).
Hydrothermal Activity
A summit collapse event, which was probably not related to an eruption, occurred between 12 and 5ka. Hydrothermally altered rocks at the scar of the collapse event, suggest that the collapse may have been the result of the circulation of hydrothermal fluids. The approximately 4km3 of material that is missing from the top of the volcano is observed in the 3km3 avalanche deposits located near the town of Consaca (Calveche, Cortes, 1997). |