Etude géophysique de la structure interne d'un dôme volcanique : le Puy de Dôme et son environnement (Chaîne des Puys, France)

Abstract : Volcanic domes are associated to violent volcanic eruptions and high explosivity indexes. Observation and monitoring of active domes (e.g. St. Helens, Unzen, Montserrat) underlined growth patterns characterized by extrusion phases, explosions and collapse events, involving the complex inner structure of these volcanic edifices. The study of the Puy de Dôme volcano (French Massif Central), a 11,000 years old trachytic lava dome, through geophysical imaging and data modelling, as well as a detailed morpho-structural analysis, allowed to build a precise model of the inner structure of the dome and provided new constraints about its growth and its evolution. The analysis of the high resolution Digital Terrain Model (0.5 m) allowed to identify distinct morphological units on the dome, as well as volcano-tectonic structures on the neighboring volcanic edifices (Petit Puy de Dôme and Puy des Grosmanaux). Different geophysical methods (Electrical Resistivity Tomography – ERT -, gravity and magnetism) have been implemented in order to study the inner structure of the dome and to characterize the initiating mechanisms of the deformations areas identified in the Puy de Dôme vicinity. The use of several methods allowed to study different, but complementary physical parameters, although the overall interpretation of the geophysical results is sometimes difficult in the case of a volcanic edifice so complex. The 2D and 3D geophysical models obtained indicate that the Puy de Dôme is based on preexisting volcanic edifices, a cluster of strombolian volcanoes whose the presence and/or the exact extension were partially unknown until now. The internal structure of the edifice, highly heterogeneous, is composed of a massive central part, encompassed of collapse breccia, and its summit part highlights evidences of a strong hydrothermal alteration, characteristic feature of volcanic domes. The upper part of the dome is defined by a carapace of consolidated rocks, a few meters thick, whereas the base of the edifice forms a talus composed of collapses and pyroclastic flows deposits associated to the dome growth. Finally, gravity and magnetic data pointed out the presence of intrusions beneath the Petit Puy de Dôme and the Puy des Grosmanaux edifices. The geometry of these intrusions, determined through different modelling approaches, and the nature of the rocks that composed them, indicate complex emplacement processes.
Document type :
Theses
Complete list of metadatas

https://tel.archives-ouvertes.fr/tel-01330753
Contributor : Abes Star <>
Submitted on : Monday, June 13, 2016 - 8:46:56 AM
Last modification on : Thursday, November 21, 2019 - 2:33:13 AM
Long-term archiving on: Wednesday, September 14, 2016 - 10:21:49 AM

File

PORTAL_2015CLF22647.pdf
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-01330753, version 1

Citation

Angélie Portal. Etude géophysique de la structure interne d'un dôme volcanique : le Puy de Dôme et son environnement (Chaîne des Puys, France). Sciences de la Terre. Université Blaise Pascal - Clermont-Ferrand II, 2015. Français. ⟨NNT : 2015CLF22647⟩. ⟨tel-01330753⟩

Share

Metrics

Record views

897

Files downloads

1473