Preprints
https://doi.org/10.5194/egusphere-2024-386
https://doi.org/10.5194/egusphere-2024-386
15 Mar 2024
 | 15 Mar 2024
Status: this preprint is open for discussion.

Evolution of fluid redox in a fault zone of the Pic de Port-Vieux thrust in the Pyrenees Axial Zone (Spain)

Delphine Charpentier, Gaétan Milesi, Pierre Labaume, Ahmed Abd Elmola, Martine Buatier, Pierre Lanari, and Manuel Muñoz

Abstract. In mountain ranges, crustal-scale faults localize multiple episodes of deformation. It is therefore common to observe current or past geothermal systems along these structures. Understanding the fluid circulation channelized in fault zones is essential to characterize the thermo-chemical evolution of associated hydrothermal systems. We present a study of a paleo-system of the Pic de Port-Vieux thrust fault. This fault is a second-order thrust associated with the Gavarnie thrust in the Axial Zone of the Pyrenees. The study focused on phyllosilicates, which permit to constrain the evolution of temperature and redox of fluids at the scale of the fault system. Combined X-ray absorption near-edge structure (XANES) spectroscopy and electron probe microanalysis (EPMA) on synkinematic chlorite, closely linked to microstructural observations were performed in both the core and damage zones of the fault zone. Regardless of their microstructural position, chlorite from the damage zone contains iron and magnesium (Fetotal/(Fetotal+Mg) about 0.4), with Fe3+ accounting for about 30 % of the total iron. Chlorite in the core zone is enriched in total iron, but individual Fe3+/Fetotal ratios range from 15 % to 40 % depending on the microstructural position of the grain. Homogeneous temperature conditions about 300 °C have been obtained by chlorite thermometry. A scenario is proposed for the evolution of fluid-rock interaction conditions at the scale of the fault zone. It involves the circulation of a single hydrothermal fluid with homogeneous temperature but several redox properties. A highly reducing fluid evolves due to redox reactions involving progressive dissolution of hematite, accompanied by crystallization of Fe2+-rich and Fe3+-rich chlorite in the core zone.

Delphine Charpentier, Gaétan Milesi, Pierre Labaume, Ahmed Abd Elmola, Martine Buatier, Pierre Lanari, and Manuel Muñoz

Status: open (until 08 May 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-386', Anonymous Referee #1, 08 Apr 2024 reply
  • CC1: 'Comment on egusphere-2024-386', Giacomo Medici, 12 Apr 2024 reply
Delphine Charpentier, Gaétan Milesi, Pierre Labaume, Ahmed Abd Elmola, Martine Buatier, Pierre Lanari, and Manuel Muñoz
Delphine Charpentier, Gaétan Milesi, Pierre Labaume, Ahmed Abd Elmola, Martine Buatier, Pierre Lanari, and Manuel Muñoz

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Short summary
Understanding the fluid circulation in fault zones is essential to characterize the thermo-chemical evolution of hydrothermal systems in mountain ranges. The study focused on a paleo-system of the Pyrenees. Phyllosilicates permit to constrain the evolution of temperature and redox of fluids at the scale of the fault system. A scenario is proposed and involves the circulation of a single highly reducing hydrothermal fluid (~300 °C) that evolves due to redox reactions.