Structure and Evolution
A major complex on the Chile/Argentina frontier, Cerro Falso Azufre is the main edifice of an elongate, arcuate complex extending about 15 km from west to east, Cordon Falso Azufre (Figure 41.1;41.2). The westernmost part of the complex is a crater chain 6-7 km long, composed of ~ 6 overlapping craters a few hundred meters in diameter. Activity may have migrated westwards along the chain because the westernmost crater is much the largest (1.5 km diameter) and most complete (Figure 41.3). Much of the activity from the craters appears to have been pyroclastic and the area proximal to the vent is blanketed with what may be a welded airfall deposit (Figure 41.3). While there are a number of extensive lava flows on both north and south flanks of the ridge, none seems particularly fresh, nor to be related to individual vents on the crater chain.
Eastward along the chain, two small, steep composite cones/lava vents are present (1 and 2), from which some pyroclastic activity has taken place. Both have apparently given rise to thick accumulations of andesitic lava; the easternmost cone appears slightly older than the westernmost. Further east along the ridge is a young dacite dome (see Figure 40.3), extruded from an obscure fissure along the crest line of the ridge, and extending 3 km southwards, covering an area of ~9 sq km. About 10 km further eastwards is a second, younger dacite extrusion (see Figure 40.3).
Falso Azufre lies in one of the most tectonically and volcanically active regions of the Central Andes in which many other volcanic centers have developed with individual histories. Several large young, recently active centers are found in an area 50 km radius from the volcano (Figure 40.3). For instance, Cerro Condor and Sierra Nevada lie to the north, Cerro Peinado to the northeast, and the Nevados Ojos del Salado to the west. Baker et al. (1987) regard the Cordon Falso Azufre and the associated vents as being part of a broad E-W trending volcanic lineament including the Ojos del Salado area, while Gonzalez-Ferran et al. (1985) include this complex in their lower Ojos del Salado Group of volcanics. The dacite domes appears to be the most recent, possibly holocene, event in the immediate vicinity if Falso Azufre.
No information is available of the current activity from Falso Azufre.
No information is available for any of these centres individually, but regional data (Baker et al., 1987) show little variation among the andesites and dacites.
Baker, P.E., O. Gonzalez-Ferran, & Rex, D.C., 1987. Geology and geochemistry of the Ojos del Salado volcanic region, Chile. Jour. Geol. Soc. Lond. 144:85-96.
Gonzalez-Ferran, O., Baker, P.E., & Rex, D.C., 1985. Tectonic-volcanic discontinuity at latitude 27°S, Andean range, associated with Nazca plate subduction. Tectonophysics 112:423-441.