Fault-Related Controls on Upward Hydrothermal Flow: An Integrated Geological Study of the Têt Fault System, Eastern Pyrénées (France)

Audrey Taillefer,Roger Soliva,Laurent Guillou-Frottier,Elisabeth Le Goff,Michel Seranne,Guillaume Martin

doi:10.1155/2017/8190109

Abstract

The way faults control upward fluid flow in nonmagmatic hydrothermal systems in extensional context is still unclear. In the Eastern Pyrénées, an alignment of twenty-nine hot springs (29°C to 73°C), along the normal Têt fault, offers the opportunity to study this process. Using an integrated multiscale geological approach including mapping, remote sensing, and macro- and microscopic analyses of fault zones, we show that emergence is always located in crystalline rocks at gneiss-metasediments contacts, mostly in the Têt fault footwall. The hot springs distribution is related to high topographic reliefs, which are associated with fault throw and segmentation. In more detail, emergence localizes either (1) in brittle fault damage zones at the intersection between the Têt fault and subsidiary faults or (2) in ductile faults where dissolution cavities are observed along foliations, allowing juxtaposition of metasediments. Using these observations and 2D simple numerical simulation, we propose a hydrogeological model of upward hydrothermal flow. Meteoric fluids, infiltrated at high elevation in the fault footwall relief, get warmer at depth because of the geothermal gradient. Topography-related hydraulic gradient and buoyancy forces cause hot fluid rise along permeability anisotropies associated with lithological juxtapositions, fracture, and fault zone compositions.

Highlights

Studying hydrothermal fluid flow through fault zones is important to understand thermal perturbations of the Earth’s crust and can provide strong constraints on deep geothermal exploration
Mapping of these faults has been mainly derived from topography ruptures observed in digital elevation model (DEM) allowing the author to make the distinction between brittle-Neogene normal faults from ductile Hercynian reverse faults and from brittle to ductilePyrenean reverse faults
We first compile hot spring features with mapping of faults and lithology on a digital elevation model (DEM) to identify which map scale structural parameters control the localization of the springs (Figure 3)

Summary

Introduction

Studying hydrothermal fluid flow through fault zones is important to understand thermal perturbations of the Earth’s crust and can provide strong constraints on deep geothermal exploration. Intense hydrothermal activity corresponding to large elevated surfaces (Figure 6) suggests that footwall elevation above the fault scarp bottom likely controls volume of meteoric water infiltrated on the ranges [10, 19], which should influence flow rates at the emergence. Based on water geochemical analyses, Krimissa [50] concludes that the Vernet-les-Bains, Thues-les-Bains, and Saint-Thomas-les-Bains hot springs are likely sourced from a unique reservoir Both relief compartmentalization related to the Tet fault segmentation, in particular the Py fault (see Figure 6), and differences of sinter compositions (see XRD analysis in Supplementary Material) question the presence of a unique convection cell and suggest the existence of a separate one underneath the Canigou Range related to the Vernet-les-Bains hot springs (Figure 10)

Methods

Results

Discussion

Conclusion