Cordon del Azufre
Structure and Evolution
The Cordon del Azufre is a small volcanic complex located in one of the remotest parts of the Central Andes, on the frontier between Argentina and Chile. Three separate components may be distinguished (Figure 37.1):
1. A lava flow cluster lying east of the main ridge itself, wholly within Argentina (I). This cluster reaches an elevation of 5,100 m at a small vent near its westernmost end, but several other vents are apparently present. Many small flows less than 1 km long are present, but the whole complex covers an area roughly 9 x 5 km. On morphological grounds, the lavas appear to be silicic (dacitic?).
2. An older part of Cordon del Azufre itself (II), which consists of four craters and associated flows, forming a well-developed north south trending chain 5 km long. Three of the craters are only a few hundred meters in diameter, but one of the older ones has a diameter of ~1 km. Lavas from this complex extend for up to 5 km on the northern and western flanks, and appear to be andesitic. They are cleary not pristine, however.
3. Volcan La Moyra (previously un-named), is the most recently active centre (C). The most prominent features of this young 300 m high young cone (Figure 37.2) are dark lava flows which extend for more than 6 km on the western flanks and 3 km on the eastern flank (L), where they slightly overide unit I. Their extremely low albedo and pristine morphologies suggest that they are young, andesitic lavas, that Naranjo & Cornejo (1992) dated at 0.3 +/- 0.3 Ma with K-Ar. Ground observations show that they are blocky flows (Figure 37.3; J.A Naranjo pers. comm. 1989). They were erupted from a well defined summit crater about 400 m in diameter. Pale grey tones on the TM image (A) and obscuration of lava flow morphologies within 1 km of the summit crater suggests a recent pyroclastic eruption which has partially buried the proximal parts of some lavas (Figure 37.1; 37.2). This pyroclastic eruption was the most recent event from the Cordon del Azufre.
InSAR ground deformation studies have detected recent ground inflation (2.5 cm/yr) from Cordon del Azufre to Lastarria and Cerro Bayo, which Froger et al. (2007) interpret as magma chamber growth due to the injection of new melt.
The youngest lava is a porphyritic andesite (59.68% SiO2; 3.58% MgO) with dominant plagioclase and subordinate euhedral hornblende, pyroxene, and rare biotite all rimmed with oxide (J.A. Naranjo and P. Cornejo, in preparation, 1990). Trace element contents are similar to typical Central Andean andesites (e.g., Sr 488 ppm; Rb 122 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.