Magma Chamber Associated to Deep Faults in Copahue Active Volcanic Complex, South America, Suggested by Magnetotelluric Study

E. Borzotta, A. T. Caselli, M. J. Mamani


Magnetotelluric studies were carried out in 1993 and 2008 inside the caldera of Copahue Volcanic Complex, located in South America, at the border between Chile and Argentina (37°45ʹ S; 71°10.2ʹ W). The main effusive centre of this complex is the Copahue Active Volcano, which constitutes an important geothermal zone. The study of the crust and the investigation of possible magma chambers were the objectives of this survey. Six magnetotelluric soundings were interpreted taking in mind the geologic and tectonic background. Two 2D bimodal modelling along two profiles approximately perpendicular to geological strike were performed. In addition, two magnetovariational studies were made, using two magnetic variometers. Induction (Wiese) vectors were thus estimated for three MT sites. Among the results, the lithosphere in the region is suggested to be 60—66 km thickness, with upper and lower crusts of 8 km and 10 km thickness respectively. A magma chamber is suggested at lower crust with top at 3—8 km depth, with 1 Ωm of resistivity, thus indicating partial-melting or melted-rocks. Data suggest this chamber could be genetically associated with a deep fault system into the caldera. Heat flows of 130—278 mW/m2 were estimated at surface, above magma chambers, using empirical formulas linking depths of thermal conductive layers, in the crust and upper mantle, with heat flows values measured at surface. The estimated heat flows, thus obtained, are rather consistent with heat flows measured in wells drilled into the caldera.

Taking into account that magnetotelluric soundings, at present, are not usual in volcanic studies, the present work may give valuable information about this active volcano, (which at present is in yellow alert), mainly because there are people living at about 15 km from the volcano or less in Argentina and Chile. In addition this study is important from geothermal point of view, for the possibility to obtain energy without air contamination.


Copahue volcano; magnetotelluric study; magma chamber; heat flows; Earth’s crust

Full Text:



Adám, A. (1978). Geothermal effects in the formation of electrically conducting zones and temperature distribution in the Earth. Physics of the Earth and Planetary Interiors, 17(2), 21—28.

Berdichevsky, M. N. & Dmitriev, V. I. (1976). Basic principles of interpretation of magnetotelluric sounding curves. In: A. Adám (ed.), Geoelectric and Geothermal Studies, KAPG Geophysical Monograph (pp. 165—221). Budapest: Akadémiai Kiadó.

Berdichevsky, M. N., Chernyavsky, G. A. & Alperovich, I. M. (1976). Deep magnetotelluric surveys in Sakhalin. In: A. Adám (ed.), Geoelectric and Geothermal Studies, KAPG Geophysical Monograph, (pp. 702—707). Budapest: Akadémiai Kiadó.

Berdichevsky, M. N., Vanyan, L. L. & Dmitriev, V. I. (1989). Methods used in the U.S.S.R. to reduce near-surface inhomogeneity effects on deep magnetotelluric sounding. Physics of the Earth and Planetary Interiors, 53(3-4), 194—206.

Brasse, H., & Soyer, W., (2001). A magnetotelluric study in the Southern Chilean Andes. Geophysical Research Letters, 28(19), 3757—3760.

Brasse, H., Kapinos, G., Li, Y., Mutschard, L., Soyer, W. & Eydam, D. (2009). Structural electrical anisotropy in the crust at the South-Central Chilean continental margin as inferred from geomagnetic transfer functions. Physics of the Earth and Planetary Interiors, 173(1-2), 7—16.

Feldman, I. S. (1976). On the nature of conductive layers in the Earth’s crust and upper mantle. In: A. Adám (ed.), Geoelectric and Geothermal Studies, KAPG Geophysical Monograph (pp. 719—730). Budapest: Akadémiai Kiadó.

Folguera, A., Ramos, V. A. & Melnick, D. (2003). Recurrencia en el desarrollo de cuencas de intraarco. Cordillera Neuquina (37°30’—38°S). Revista de la Asociación Geológica Argentina, 58(1), 3—19.

Gonzalez Diaz, E. F. (2005). Geomorfología de la region del volcán Copahue y sus adyacencias (centro-oeste del Neuquén). Revista Asociación Geológica Argentina, 60(1), 72—87.

Jones, A. G. (1992). Electrical conductivity of the continental lower crust. In: D. M. Fountain, R. J. Arculus & R. W. Kay (Eds.), Continental Lower Crust (Chapter 3, pp. 81—143). Elsevier.

Mamani, M. J., Borzotta, E., Venencia, J. E., Maidana, A., Moyano, C. E. & Castiglione, B. (2000). Electric structure of the Copahue Volcano (Neuquén Province, Argentina), from magnetotelluric soundings: 1D and 2D modellings. Journal of South American Earth Sciences, 13(1-2), 147—156.

Mas, L., Mas, G. & Bengochea, L. (2000). Heat flow of Copahue geothermal field, its relation with tectonic scheme. Proc. World Geothermal Congress. Kyushu-Tohoku, Japan, May 28—June 10 (pp.1419—1424).

Melnick, D., Folguera, A. & Ramos, V. A. (2006). Structural control on arc volcanism: The Caviahue-Copahue complex, Central to Patagonian Andes Transition (38° S). Journal of South American Earth Sciences, 22(1-2), 66—88.

Muñoz, M., Fournier, H., Mamani, M., Febrer, J., Borzotta, E. & Maidana, A. (1990). A comparative study of results obtained in magnetotelluric deep soundings in Villarrica active volcano zone (Chile) with gravity investigations, distribution of earthquake foci, heat flow empirical relationships, isotopic geochemistry 87Sr/86Sr and SB systematics. Physics of the Earth and Planetary Interiors, 60(1-4), 195—211.

Naranjo, J. A. & Polanco, E. (2004). The 2000 AD eruption of Copahue Volcano, Southern Andes. Revista geológica de Chile, 31(2), 279—292.

Pesce, A. H. (1989). Evolución volcano-tectónica del Complejo Efusivo Copahue-Caviahue y su modelo geotérmico preliminary. Revista Asociación Geológica Argentina, XLIV(1-4), 307—327.

Radic, J. P. (2010). Las cuencas cenozoicas y su control en el volcanismo de los Complejos Nevados de Chillán y Copahue-Callaqui (Andes del Sur, 36—39°S). Andean Geology, 37(1), 220—246.

Rokityansky, I. I. (1982). Geoelectromagnetic Investigation of the Earth’s Crust and Mantle. Springer.

Stern, Ch. R. (2004). Active Andean volcanism: its geologic and tectonic setting. Revista geológica de Chile, 31(2), 161—206.

Wannamaker, P. E., Stodt, J. A., & Rijo, L. (1987). Finite element program for solution of magnetotelluric responses of two-dimensional Earth resistivity structure. Earth Science Laboratory, University of Utah, Research Institute.


  • There are currently no refbacks.

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Creative Commons License
Geofizicheskiy Zhurnal is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Flag Counter