Structure and Evolution
Cerro Bayo is a small, obscure volcanic complex located in a remote part of the cordillera on the frontier between Chile and Argentina. Three principle structural units may be distinguished (Figure 38.1):
(1) An older center (I), the source of a number of lava flows which spread westwards towards the Salar de Gorbea and also due north. The morphology of this older lava group suggests an andesitic composition. A poorly preserved crater ~800 m in diameter in the summit region may have been associated with this episode.
(2) A younger cone with a well preserved crater ~400 m in diameter located east of the summit region from which lavas have flowed to the north and northwest (II).
(3) Two thick, pale toned dacite coulées (D) which extend north-westwards for 2-3 km from the source vent which appears to form the highest point on the present volcano. These have the typical pronounced flow ridges or ogives expected from lavas of silicic compositions, and the northern lobe has well developed levées. They are the most recent events from the Cerro Bayo complex.
The lavas are mainly hydrothermal altered and one has been dated using K-Ar to 1.6±0.4 Ma by Naranjo and Cornejo (1992).
InSAR ground deformation studies have detected recent ground inflation (2.5 cm/yr) from Cerro Bayo to Lastarria and Cordon del Azufre, which Froger et al. (2007) interpret as magma chamber growth due to the injection of new melt.
Naranjo and Cornejo report that the dacite (65.0% SiO2; 3.96% K2O) of the dome is typically porphyritic with plagioclase, biotite, hornblende, hypersthene, and augite set in a fresh glass. Xenocrystic clots of augite are common. Trace elements are typical of other CVZ dacites (e.g., Sr 410 ppm; Rb 192 ppm).
Froger, J.-L., Remy, D., Bonvalot, S., Legrand, D., 2007. Two scales of inflation at Lastarria-Cordon del Azufre volcanic complex, central Andes, revealed from ASAR-ENVISAT interferometric data, Earth and Planetary Science Letters, 255(1-2):148-163.
Naranjo, J. and Cornejo, P., 1992. Hoja Salar de la Isla-Carta Geologica de Chile, No. 72, 1:250000 Servicio National de Geologia y Mineria, Santiago, Chile.