Escalante & Sairecabur
Structure and Evolution
Extending for ~22km N-S, this linear complex assemblage of volcanoes (Figure 22.1), adjoins Volcan Putuna (q.v.; P) in the north and extends from Escalante (or Apagado; E) in the north to Sairecabur (S) in the south and defines the frontier between Chile and Bolivia. Nomenclature for this assemblage is confused, owing to conflicting usages on Chilean and Bolivian topographic maps. At least 10 distinct post-glacial centres are present, all of which have several youthful lava flows associated with them. A lava from one of the ancestral centres (pre-Holocene) extends for about 30 km SW of the chain (L1). The most conspicuous recent centres are Escalante and Sairecabur, and two unnamed centres (1 and 2) located wholly on the Bolivian side of the frontier.
Sairecabur (5, 971 m) is the highest edifice in the chain. It is located on the northern part of the 4.5 km diameter caldera of an older, pre-Holocene volcano. Post-glacial activity was initiated at a centre just to the south, as evidenced by several short young lava flows, but the youngest activity is represented by the pristine, dark lava flows of Sairecabur (L), which extend about 2.5km to the NW. Escalante has a large, slightly degraded summit crater containing a small lake, and has morphologically youthful lava flows on its flanks. It is also largely post-glacial, although activity there has not been as recent as at Sairecabur. Unamed Centre 1 has a pristine summit crater and fresh but not dark lava flows. 2 lacks a crater but also appears to have been a prolific lava producer in post-glacial times.
Low-albedo lavas from Sairecabur represent the most recent activity from this chain. No contemporary fumarolic activity has been reported , but extensive earlier fumarolic activity is indicated by altered material washing down the eastern flanks. An active sulphur mine is located at Saciel, north of Sairecabur.
No activity at the present day is known; the whole chain appears to be dormant.
The lavas from Escalante and Sairecabur are very similar and are typically grey to black, porphyritic, pyroxene andesites (Deruelle,1978; Marinovic & Lahsen, 1984). Phenocryst contents vary from 20-40%, and are dominantly plagioclase (An34-52), Ca-augite, bronzite and opaques with rare hornblende, biotite and quartz. Reconnaissance work by Harmon et al (1984) show that Sairecabur lavas (59.4 - 60.6% SiO2) are characterized by d18O of 9.0, 87Sr/86Sr of 0.70821-0.70865, and Pb isotopic ratios of 18.83, 15.65, and 38.81 (206/204, 207/204, 208/204 respectively) which are typical for CVZ lavas.
Deruelle, B., 1978., Calc-alkaline and shoshonitic lavas from five Andean volcanoes (between latitudes 21°45' and 24°30'S) and the distribution of the Plio-Quaternary volcanism of the south-central and southern Andes. Jour. Volcanol. Geotherm. Res. 3:281-298
Harmon, R.S., Barreiro, B.A., Moorbath, S., Hoefs, J., Francis, P.W., Thorpe, R.S., Deruelle, B., McHugh, J., and Viglino, J.A., 1984. Regional O-, Sr- and Pb-isotope relationships in late Cenozoic calc-alkaline lavas of the Andean Cordillera. J. Geol. Soc. Lond., 141:803-822
Marinovic, N. & Lahsen, A., 1984. Hoja Calama. Carta Geologica de Chile No. 58. S.N.G.M. Santiago, Chile.