Geological Summary

The composite volcano of San Pedro in the arid Atacama desert of northern Chile has a basaltic andesite-to-dacitic edifice and is 6 km W of the older San Pablo. The youngest cone was constructed within an arcuate escarpment left by the collapse of an older edifice, which produced a large debris avalanche to the west, perhaps accompanied by a major pumice eruption. Thick dacitic lava flows with steep-sided fronts mantle the upper portion of the younger cone. Reports of variable reliability mention eruptions in the 19th and 20th centuries, but no corresponding deposits have been identified. The youthful-looking La Poruña scoria cone on the W flank produced an 8-km-long lava flow, but Worner et al. (2000) obtained a Helium surface-exposure age of 103,000 years from a juvenile block of the lava flow. González-Maurel et al. (2019) obtained ⁴⁰Ar/³⁹Ar ages using unaltered groundmass from fresh La Poruña samples of 92 ± 34 and 110 ± 11 ka; for San Pedro, an ⁴⁰Ar/³⁹Ar groundmass age of 96 ± 8 ka was measured.

References

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography.

Casertano L, 1963. Chilean Continent. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 15: 1-55.

de Silva S L, Francis P W, 1991. Volcanoes of the Central Andes. Berlin: Springer-Verlag, 216 p.

Francis P W, Roobol M J, Walker G P L, Cobbold P R, Coward M, 1974. The San Pedro and San Pablo volcanoes of northern Chile and their hot avalanche deposits. Geol Rundschau, 63: 357-388.

Gonzalez-Ferran O, 1995. Volcanes de Chile. Santiago: Instituto Geografico Militar, 635 p.

González-Maurel O, Godoy B, le Roux P, Rodríguez I, Maríne C, Menzies A, Bertin D, Morata D, Vargas M, 2019. Magmatic differentiation at La Poruña scoria cone, Central Andes, northern Chile: Evidence for assimilation during turbulent ascent processes, and genetic links with mafic eruptions at adjacent San Pedro volcano. Lithos, 338–339: 128–140. https://doi.org/10.1016/j.lithos.2019.03.033

IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome, International Association of Volcanology and Chemistry of the Earth's Interior.

O'Callaghan L J, Francis P W, 1986. Volcanological and petrological evolution of San Pedro volcano, Provincia El Loa, north Chile. Journal of the Geological Society, 143: 275-286.

Worner G, Hammerschmidt K, Henjes-Kunst F, Lezaun J, Wilke H, 2000. Geochronology (40Ar/39Ar, K-Ar and He-exposure ages) of Cenozoic magmatic rocks from Northern Chile (18-22° S): implications for magmatism and tectonic evolution of the central Andes. Rev Geol Chile, 27: 205-240.