Propriétés electromagnetiques de l'altération hydrothermale à différentes profondeurs.

par Léa Levy

Projet de thèse en Sciences de la Terre et de l'environnement

Sous la direction de Pierre Briole et de Freysteinn Sigmundsson.

Thèses en préparation à Paris Sciences et Lettres en cotutelle avec l'University of Iceland , dans le cadre de Sciences de la Terre et de l'environnement et physique de l'Univers Paris , en partenariat avec Laboratoire de Géologie de l'Ecole Normale Supérieure (laboratoire) et de Ecole normale supérieure (établissement de préparation de la thèse) depuis le 01-10-2015 .


  • Résumé

    The PhD focuses on hydrothermal alteration and its geophysical signatures. The plan is to address the following questions. (1) What is the electrical response of the different alteration minerals found in high-temperature hydrothermal systems? Beside ionic conduction in pores, processes such as surface conduction, induced polarization, semi-conduction and melt conduction are crucial to understand the bulk conductivity signal. While semi-conduction may occur in presence of pyrite or magnetite, surface conduction and polarization are mainly related to the cation exchange properties of clays and zeolites. The first part of the PhD aims at understanding the various electrical phenomena occuring in different families of clays and zeolites. In the second part, laboratory resistivity measurements of core samples containing high-temperature minerals (chlorite, epidote, actinolite) will be performed in a wide range of temperatures and pressures to study the evolution of their electric properties. (2) How can resistivity surface soundings provide insights on the current activity of hydrothermal systems? Cooled sections of hydrothermal systems are encountered in active volcanic zones. Yet their electrical signature is similar to hotter sections, as most of high-temperature alteration minerals remain stable once they formed. The low-temperature mineralogy signature of such systems is investigated. (3) How can surface alteration be complementary to resistivity soundings to assess the activity of hydrothermal systems? This part of the PhD is more open and will be treated at last, using airborne and satellite hyperspectral mapping of surface alteration.

  • Titre traduit

    Electromagnetic properties of hydrothermal alteration at varying depths.


  • Résumé

    The PhD focuses on hydrothermal alteration and its geophysical signatures. The plan is to address the following questions. (1) What is the electrical response of the different alteration minerals found in high-temperature hydrothermal systems? Beside ionic conduction in pores, processes such as surface conduction, induced polarization, semi-conduction and melt conduction are crucial to understand the bulk conductivity signal. While semi-conduction may occur in presence of pyrite or magnetite, surface conduction and polarization are mainly related to the cation exchange properties of clays and zeolites. The first part of the PhD aims at understanding the various electrical phenomena occuring in different families of clays and zeolites. In the second part, laboratory resistivity measurements of core samples containing high-temperature minerals (chlorite, epidote, actinolite) will be performed in a wide range of temperatures and pressures to study the evolution of their electric properties. (2) How can resistivity surface soundings provide insights on the current activity of hydrothermal systems? Cooled sections of hydrothermal systems are encountered in active volcanic zones. Yet their electrical signature is similar to hotter sections, as most of high-temperature alteration minerals remain stable once they formed. The low-temperature mineralogy signature of such systems is investigated. (3) How can surface alteration be complementary to resistivity soundings to assess the activity of hydrothermal systems? This part of the PhD is more open and will be treated at last, using airborne and satellite hyperspectral mapping of surface alteration.