Cerro Purico Ignimbrite Center

Bolivia
Synonyms: None
Location: 22º57'S; 67º45'W
Average/Max Elevation: 4900m/5900m
Caldera Diameter: 3km x 3km
Volume: ~1000 cub. km
Age Range: 1.3 to 0 Ma

Volcano Image

The youngest of the ignimbrite centres which make up the LPC is the Purico Complex (23º00'S; 67º4'W), located approximately 30 km east of San Pedro de Atacama on the northwestern margin of the La Pacana caldera. Its roughly radial symmetry and the low angle dips of the ignimbrite mantled flanks of the complex led Baker (1981) to describe it as an ignimbrite "shield". It seems likely, however, that these dips may reflect the pre-eruption topography and may therefore not be constructional phenomena associated solely with the ignimbrite centre. Two ignimbrite units are present. The older and more extensive is the 1.3 Ma Lower Purico ignimbrite which forms the upper surface of the regional slope west of the center. This ignimbrite now covers an area of ~800 km2 and is up to 100m thick. The Upper Purico ignimbrite occurs mainly on the summit regions of the complex (~4500 - 5000m) and to the east on the caldera wall and moat of the La Pacana caldera. A 0.8 Ma old dacitic dome ('Dome D' of Francis et al., 1984) was the final phase of the upper Purico ignimbrite eruption and lies on the northern side of a 1 km diameter shallow depression which may mark the source vent of the ignimbrites. Schmitt et al. (2001) describes a strong compositional similarity between the domes and the ignimbrites, and reports a slightly older age for Dome D (0.98). Mafic recharge has been implicated as the initiator of the formation of numerous Holocene domes in the complex (Cerros Purico, Negro, Putas, Chascon, Aspero, and El Cerillo; Schmitt et al., 2001).

References

Baker, M.C.W., 1981. The nature and distirbution of upper Cenozoic ignimbrite centres in the Central Andes. J. Volcanol. Geotherm. Res. v11, p293-315.

Francis, P.W., McDonough, W., Hammill, M., O'Callaghan, L.J., & Thorpe, R.S., 1984. The Cerro Purico volcanic complex, north Chile. In: Andean Magmatism - Chemical and isotopic constraints. R.S. Harmon & Barreiro B. (eds.) Shiva publishing, Orpington, UK. p106-123.

Schmitt, A., de Silva, S., Trumbull, R., and Emmermann, R., 2001. Magma evolution in the Purico ignimbrite complex, northern Chile: evidence for zoning of a dacitic magma by injection of rhyolitic melts following mafic recharge. Contributions to Mineralogy and Petrology, 140(6): 680-700.