Cerro Porquesa

Cerro Porquesa is an approximately 4,600 metres (15,100 ft) high[1] (800 metres (2,600 ft) above base)[2] rhyodacite lava dome in the Andes.[3] The lava dome is of Pliocene/Pleistocene age[4] with little glacial features on the younger domes indicating young ages.[1]

False colour satellite image of the Cerro Porquesa lava domes (grey-violet) in the centre.

The dome was formed in at least three different eruption stages, with each stage contributing about two or three different lobes. Further, a rhyolitic ignimbrite with 69.5% SiO2 may be linked to the domes. It fills a valley in the south of the complex about 2 metres (6 ft 7 in) thick.[1] This ignimbrite is dated 0.73±0.16 and 0.63 +0.92/-0.63 mya by potassium-argon dating in biotite, although with low precision.[2]

This lava dome is located 20° in a volcanic gap named Pica gap. In this gap volcanic activity younger than 2 mya isn't found and where lead (Pb) isotope ratios in rocks change with the radiogenicity of the isotope ratio decreasing northward. Porquesa has intermediary isotope ratios. The lower ratio was principally imparted by the low-radiogenic Pb upper crust.[3] Samples and the appearance of the domes in aerial photographs indicate a homogeneous composition with about 68% SiO2.[1]

References
  1. Worner, Gerhardt; Moorbath, Stephen; Horn, Susanne; Entenmann, Jürgen; Harmon, Russel S.; Davidson, Jon P.; Lopez-Escobar, Leopoldo (1994). Tectonics of the Southern Central Andes Structure and Evolution of an Active Continental Margin. Berlin, Heidelberg: Springer Berlin Heidelberg. pp. 77–88. doi:10.1007/978-3-642-77353-2_5. ISBN 978-3-642-77353-2.
  2. Wörner, Gerhardt; Hammerschmidt, Konrad; Henjes-Kunst, Friedhelm; Lezaun, Judith; Wilke, Hans (December 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". Revista geológica de Chile. 27. Retrieved 8 December 2015.
  3. Wörner, Gerhard; Moorbath, Stephen; Harmon, Russel S. (1992). "Andean Cenozoic volcanic centers reflect basement isotopic domains". Geology. 20 (12): 1103–1106. doi:10.1130/0091-7613(1992)020<1103:ACVCRB>2.3.CO;2.
  4. Worner, Gerhardt; Lopez-Escobar, Leopoldo; Moorbath, Stephen; Horn, Susan; Entenmann, Jürgen; Harmon, Russel S.; Davidson, Jon D. (1992). "Variaciones geoquimicas, locales y regionales, en el frente volcanico cuaternario de los Andes centrales (17°30'-22°00'S), norte de Chile". Andean Geology. 19 (a). Archived from the original on 22 March 2017. Retrieved 8 December 2015.

"Porquesa". Global Volcanism Program. Smithsonian Institution.

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