Structure and Evolution
Located to the south of the Salar de Antofalla and Laguna del Peinado in Argentina, east/northeast of the Ojos del Salado region, Peinado (Figure 41.1) is at the heart of the most tectonically and volcanically active region in the Central Andes. Reconnaissance mapping of the region was conducted during the period 1970 - 1972 (Gallucci, 1972; O. Gonzales pers. comm. 1989). Peinado appears to to be extremely youthful, and its eruptive activity may be related to the recent period of extensional stress which has prevailed throughout this part of Argentina (e.g. Allmendinger et. al., 1989).
The upper part of the simple, symmetrical cone is largely composed of very dark pyroclastic probably of andesitic composition(Figure 41.2; 41.3). No distinct crater can be detected in the summit region which is slightly altered. Two tongues of light grey toned material on the northern side of the cone may be more silicic pyroclastic flows (PF). An extensive apron of dark lava flows extends outwards to a distance of almost 6 km from the cone. The flows are pristine, with excellent levée morphologies typical of andesite or basaltic andesite compositions. Most of the lavas have been erupted from vents on the lower parts of the cone (i.e. S) and several spatter accumulations can be detected on stereo air photographs. In the lower elevations the lava flows have a coating of aeolian dust derived from the basement ignimbrites and salars to the west - some excellent "yardangs" can be seen on the ignimbrites immediately to the west of the cone. Peinado is surrounded by several small monogenetic and polygenetic vents from which many extensive mafic lava flows have erupted. These vary in form from simple cinder cones and maars, to nested cones and vents to small monogenetic fields (i.e. L ) located along recent north south trending normal faults. These are all included as monogenetic centers of the Salar de Antofalla region (section 3.2.1).
Most of Peinado is young and it is difficult to differentiate any particular event as being more recent than any other. However, the volcano is clearly one of the youngest major edifices in the region and merits further study.
A visit by geologists of the Universidad Nacional de Tucuman in 1972 showed no evidence of activity.
Allmendinger-R.W., Eremchuck-J.E., Sosa-Gomez-J, Ojeda-J, and Francis-P.W. (1989). The Pasto-Ventura pull-apart and the southward collapse of the southern pun plateau. J. Latin Am. Earth Sci., 2, 111-130.
Gallucci, A.R., 1972. Informe preliminar: Mosaico 17-C.4. NOA-1 Geologico Minero Jefatura de Tucuman. San Miguel de Tucuman. 6pp.