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Geology of Volcán Villarrica
The objective of this page is to provide a brief overview of the geology of Volcán Villarrica, and to give you a view of salient features of the volcano in the field. Emphasis is arbitarily oriented towards my interests, in particular the Pucón Ignimbrite.
Volcán Villarrica is located at 39o25'S, in the central Southern Andean Volcanic Zone (SAVZ). It is the westernmost of three large Quaternary volcanic complexes (the Villarrica-Lanín Chain) located along a prominent, northwest trending offset of the Liquiñe-Ofqui Fault, a major dextral shear zone (López-Escobar and Moreno, 1994a). Hickey-Vargas et al. (1989) and Tormey et al. (1991) describe the petrological and geochemical, and isotopic features of this system of volcanoes, and spatially associated basaltic satellite volcanoes. Hickey-Vargas et al. (1989), López-Escobar and Moreno, 1994, Moreno (1996) and Clavero (1996), defined detailed profiles of the stratigraphy, petrology and geochemistry of Volcán Villarrica itself. The volcano consists dominantly of basaltic to basaltic andesite flows and interbedded tephra. Evolution of volcano is divided into three main phases (V-1, V-II and V-III), consisting of stratovolcano development puntuated by voluminous, caldera-forming eruptions of the 14 Ka Licán and 7 Ka Pucón Ignimbrites (López-Escobar and Moreno, 1994; Moreno, 1996; Clavero, 1996).
Volcán Villarrica is dominantly mafic consisting largely of a compositionally narrow range of basalts and basaltic andesites. The rocks are isotopically primitive, having Sr-, eNd, and O-isotopic ratios of ~0.704, +5, and +5.8, respectively (Hickey-Vargas et al., 1989; Déruelle et al., 1983). López-Escobar and Moreno (1994b) make the important point that eruption of mafic pyroclastic flows correlate with chemically more evolved compositional features (e.g., increased Metal-Oxide/MgO and Al2O3/CaO ratios). However, the extent of chemical evolution chemical is uncorrelated with the volumes of the explosively erupted deposits. Clavero (1996) recently completed an exemplary thesis study of the two most voluminous ignimbrites, focusing on physical volcanology of the deposits, but also including considerable geochemical and petrological characterizations of pyroclasts. Clavero demonstrates that the ignimbrite extends roughly radially 10-15 km from the modern Villarrica cone, and has a volume of 5 km3. The deposit consists of multiple nonwelded massive-flow and pyroclastic-surge-type facies, the later of which is commonly controlled by topographic obstacles.
|Active volcanism in the Andean Mountain Range is segmented into three distinct zones (active volcanoes are shown in red). Volcán Villarrica is located near the center of the southern Andean volcanic zone. South American volcanoes are graphically indexed at the Smithsonian web site.|
A simplified geologic map of the Villarrica-Lanín Volcanic Chain; Volcán Villarrica is shown in red. The region of dispersal of the Pucón Ignimbrite is shown by the blue-line (Clavero, 1996). The bold black lines at the center of the volcano represent outlines of calderas produced during eruption of the Licán (14 Ka) and Pucón (3.7 Ka) Ignimbrites. The current volcanic edifice has largely filled-in the smaller of the two calderas.
Werner Keller and Boris Behncke have published an excellent account of the history of Volcán Villarrica. The detailed account is in Spanish>; however, there is an English summary.
|Summary of the evolution of Volcán Villarrica - Stages I and II.|
|Summary of the evolution of Volcán Villarrica - Stage III.|
|View to the south of Villarrica's northern flank. A slight break in slope denotes the boundary of the original V-II caldera. This 2-km-diameter caldera formed at 3.7 Ka in response to eruption of the Pucón Ignimbrite. The larger, 14 Ka, 5-km-diamter, V-I caldera is obscured by more recent volcanic deposits. Fragments of the eastern part of this caldera are preserved to the east.|
|Diagrammatic cut-away of the volcano illustrating an inferred shallow magma chamber, magmatic plumbing, and associated hydrothermal system.|
|Go to page 2 of the "Geology of Villarrica Photo Album"|
List of References:
1. Clavero, J., 1996, Ignimbritas andesítico-basálticas postglaciales del Volán Villarrica, Andes del Sur (39o25'S). Tesis de Magister en Ciencias, Universdad de Chile, Santiago, 112 pp.
2. Clavero, J. and Moreno, H., 1994, Ignimbritas Licán y Pucón: Evidencias de erupciones explosivas, andesítico-basálticas, postglaciales, del Volcán Villarrica, Andes del Sur, 39o25'S. In Congreso Geológico Chileno, No. 7, Actas, Vol. 1, p. 250-254.
3. Cuadros, J., Caballero, E., Huertas, F.J., De Cisneros, C.J., Huertas, F., and Linares, J., 1999, Experimental alteration of volcanic tuff: smectite formation and effect on 18O isotope composition. Clays and Clay Mineralogy, Vol. 47, p. 769-776.
4. Freundt, A., and Schmincke, H., 1995a, Eruption and emplacement of a basaltic welded ignimbrite during caldera formation on Gran Canaria. Bull. of Volcanology, Vol. 22, p. 193-202.
5. Hickey-Vargas, R., Moreno, H., López, L., and Frey, F., 1989, Geochemical variations in Andean basaltic and silicic lavas from the Villarrica-Lanín volcanic chain (39.5oS): An evaluation of source heterogeneity, fractional crystallization and crustal assimilation. Contributions to Mineralogy and Petrology, Vol 103, p. 361-386.
6. López-Escobar, L., and Moreno, H., 1994a, Geochemical characteristics of the southern Andes basaltic volcanism associated with the Liquiñe-Ofqui fault zone between 39o and 46oS. In Congreso Geológico Chileno, No. 7, Actas, Vol. 2, p. 1388-1393.
7. López-Escobar, L., and Moreno, H., 1994b, Contribution to the knowledge of the postglacial geochemical evolution of the Villarrica Volcano (Southern Andes, 39o25'S). In Congreso Geológico Chileno, No. 7, Actas, Vol. 2, p. 1091-1094.
8. Moreno, H., 1995, Volcán Villarrica: Geología y riesgo volcánico. Manuscrito inédito de Servicio Nacional, de Geología y Minería, 132 pp.
9. Hildreth, W., Christiansen, R.L., and O'Neil, J.R., 1984, Catastrophic isotopic modification of rhyolitic magma at times of caldera subsidence, Yellowstone Plateau volcanic field. Jour. Geophyiscal Research, Vol. 89, p. 8339-8369.
10. Mastin, L.G., and Ghiorso, M.S., 2000, A Numerical Program for Steady-State Flow of Magma-Gas Mixtures Through Vertical Eruptive Conduits. U.S. Geological Survey Open-File Report 00-209, 61 pp.
11. Morimoto, N. Fabries, J., Ferguson, A.K.,Ginzburg, I.V., Ross, M., Seifert, F.A., Zussman, J., Aoki-K., and Gottardi-G., Nomenclature of pyroxenes. American Mineralogist, Vol 73, p. 1123-1133.
12. Rapela, C.W., and Pankhurst, R.J., 1996, Monzonite suites: the innermost Cordilleran plutonism of Patagonia. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 87, p. 193-203.
13. Sisson, T.W., and Grove, T.L., 1993a, Experimental investigations of the role of H2O in calc-alkaline differentiation and subduction zone magmatism. Contributions to Mineralogy and Petrology, Vol. 113, p. 143-166.
14. Sisson, T.W., and Grove, T.L., 1993b, Temperatures and H2O contents of low-MgO high-alumina basalts. Contributions to Mineralogy and Petrology, Vol. 113, p. 167-184.
15. Smith, R.L., 1979, Ash-flow magmatism. In, Chapin, C.E. and Elston, W.E., "Ash-Flow Tuffs," Geological Society of America Special Paper 180, p. 5-27.
16. Taylor, H.P., Jr., 1986, Igneous rocks: II. Isotopic case studies of circumpacific magmatism. In, Valley, J.W., et al., eds., Stable Isotopes in High Temperature Geological Processes, Reviews in Mineralogy, Vol. 16, p. 273-317.
17. Tormey, D.R., Hickey-Vargas, R., Frey, F.A., and López-Escobar, L., 1991, Recent lavas from the Andean volcanic front (33 to 42oS); interpretations of along-arc compositional features. In, Harmon, R.S., and Rapela, C.W., eds., Andean magmatism and its tectonic setting," Geological Society of America Special Paper 265, p. 57-77.
18. Zimanowski, B., 1998, Phreatomagmatic explosions. In, Freundt, A., and Rosi, M., eds., "From Magma to Tephra," Elsevier Science Ltd., Amsterdam, p. 25-51.