The Link between Fluid Flow, Structure and Hydrothermal Inputs in Central Chile: An Interdisciplinary Approach for Low-Enthalpy Andean Hydrogeothermal Modeling

Abstract:

The interaction between fault zones and hydrogeological domains are an open challenge and require the understanding of the complex relationship between structure, fluid flow and hydrothermal transport and processes. Faults stimulate hydraulic conductivity when acting as conduit, but it can also be a barrier by mineral precipitation and comminution. Structural heterogeneity of fractured lithology induces a flow partition within the aquifer system creating preferential flows paths and some fracture connectivity. We propose an interdisciplinary approach from hydrogeological and structural point of view, in a low-enthalpy aquifer system in the central valley of Central Chile, where several low-temperature thermal springs are spatially related to regional long-lived fault zone (Pocuro Fault Zone). Pocuro Fault zone is a kilometric NS-striking steeply dipping fault zone, with at least 50 km long. Metric wide fault core includes gouge and cataclastic rocks, whereas decametric damage zone consists of intensely fractured and hydrothermal altered Meso-Cenozoic volcanic and volcaniclastic host rocks, crossed by centimetric to milimetric subvertical NE-striking veins. Preliminary results of vein infill clays minerals and zeolites from damage zone, suggest P-T conditions interpreted as an exhumed fossil high-temperature (120º-230ºC) geothermal system. Currently, only low-temperature thermal springs are discharging with different geochemical patterns (bicarbonate to chlorine and sulphate dominant ions) and a homogeneous temperature range (20º-25ºC). This is an interesting study case, to better understand the permeability evolution of geothermal system and the link between internal fault architecture, hydrogeology and hydrothermal inputs.