| Title | Fault-Controlled Fluid Flow in Fractured Geothermal Systems: Structural Control on the Development of the Liquiñe Area, Southern Volcanic Zone of the Andes (39ºS) |
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| Authors | Gloria ARANCIBIA, Tomas ROQUER, Julie ROWLAND, Andrés VELOSO, Eduardo MOLINA, Josefa SEPULVEDA, Jorge CREMPIEN, Diego MORATA |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Fault zones and fluid flow, Liquiñe-Ofqui Fault System, Andean Tranverse Faults, Southern Volcanic Andean Zone |
| Abstract | Fault zones and fracture networks control the spatial distribution and development of fluid flow in the upper crust, by acting by conduit or barriers for crustal fluid flow (e.g. magma and groundwater flow). The nature of long and short-term geological conditions for fluid flow in fault zones, is critical to know the tectono-hydraulic behavior on natural fractured systems. We propose the Southern Volcanic Zone (Southern Andes, Chile) as a case study to evaluate the role of the structural permeability in primarily low porosity crystalline rocks of the North Patagonian Batholith. Recently published work propose a relatively well-constrained first-order role of two active fault systems in fluid flow at crustal scales: the arc-parallel (NNE-striking) Liquiñe Ofqui Fault System (LOFS) and the arc-oblique (NW to WNW-striking) Andean Transverse Faults (ATF). Such role depends on the elastic response of the intra-arc in the different phases of the Andean Seismic Cycle. The LOFS is composed of active NNE-striking dextral and dextral-reverse master faults, favorably oriented for vertical fluid flow during long-term stress conditions (Andean interseismic). The ATF include a group of NW to WNW-striking morphotectonic lineaments, and sinistral and sinistral-reverse faults associated with long-lived discontinuities of the Andean basement. The ATF is unfavorably oriented for vertical fluid flow in the long-term stress conditions and would therefore favors the storage of hydrothermal fluids. However, vertical fluid flow would be enhanced at short-term stress conditions for this fault system (Andean co- and postseismic). Preliminary results indicate the occurrence of low-to-medium enthalpy geothermal system, where natural hot springs upwelling from fractured granite or from fluvial deposits overlying granitoids, spatially related to regional mapped faults and morphotectonic lineaments of the faults governing regional tectonics (LOFS and ATF). We now propose to examine the Liquiñe (~39°S) area as a site of interaction between these fault systems, in order to evaluate the naturally fractured geothermal system. We collected and inverted fault-slip data in 2 selected structural sites, Los Añiques (n=70) and Cachim, (n=44), to propose long-term strain tectonic solutions. Each of the studied sites shows 2 tectonic solutions of strain that essentially interchange the orientations of the shortening (P) and extension axes (T) keeping the intermediate axis vertical, compatible with strike-slip regime. In Los Añiques, Solution I has P=240/04 and T=330/25, whereas Solution II has P=300/17 and T=210/02. In Cachim Solution I has P=260/01 and T=170/14, whereas Solution II has P=175/21 and T=265/05. Solution I is kinematically coupled with long-term stress conditions, whereas solution II seems to be decoupled and it is therefore likely related to local and/or sporadic stress perturbations (e.g. Andean Seismic Cycle). Our results confirm that tectono-hydraulic behavior of the geothermal system of Liquiñe is controlled by varying kinematic conditions, rather than by homogeneous strain. |