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Controls on the Southern Andean Nevados de Chillán Geothermal System

John Browning 1, Valentina Mura1, Gloria Arancibia1, David Healy2, Camila López-Contreras 1, Isa Oyarzo-Céspedes1, Jorge Crempien1, Santiago Maza3,^ ^Diego Morata 3,

  • Affiliations: 1Department of Structural and Geotechnical Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile, 2School of Earth and Environment, University of Leeds, Leeds, UK, 3Department of Earth Sciences, University of Chile, Santiago, Chile 

  • Presentation type: Talk

  • Presentation time: Tuesday 09:00 - 09:15, Room S160

  • Programme No: 5.1.3

  • Theme 5 > Session 1

Abstract

The active Nevados de Chillan volcano in the Southern Volcanic Zone of Chile presents evidence of an abundant geothermal reservoir but constraints on its size, form and depth have so far remained elusive. To remedy this, we report on combined results from structural geology surveys, experimental rock physical property analysis, surface temperature monitoring as well as clay mineralogy and finite element method temperature flow modelling. The basement of the volcano consists of four main lithologies; granodiorites with porosities of <2% and stiffnesses around 80 GPa, softer (between 50 to 70 GPa) contact hornfels with porosities <3%, diorites with a large range of porosity from around 3 to 8% and stiffnesses ranging 30 to 65 GPa, and volcaniclastic units with porosities as high as 13 % and stiffnesses as low as 10 GPa.  A series of high-angle sinistral, and low angle reverse, faults appear to control local fluid flow as evidenced by links between high temperatures (95°C) and intense argillic hydrothermal alteration in lineated surface fumarole features. Quantification of fracture attributes, from specimen to outcrop scale, their respective response to crustal stress and their tendency to dilate or slip, allowed us to hypothesize that the current reservoir resides predominantly in granitic rocks of Miocene age. Numerical and analytical modelling indicates heat fluxes ranging from 0.1 to 0.7 W/m^2  ^and the estimated geothermal energy potential of the system is around 39±1 MWe.