Ascent and degassing of basaltic magmas : case studies in Iceland and in the Chaîne des Puys (France)

• Main Author: Haddadi, Baptiste
• Other Authors: Laboratoire Magmas et Volcans (LMV), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Clermont Auvergne 2017-2020 (UCA 2017-2020 )-Centre National de la Recherche Scientifique (CNRS), Université Blaise Pascal - Clermont-Ferrand II, Didier Laporte, Olgeir Sigmarsson
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2016
• Subjects: Grímsvötn; Holuhraun; Puys de La Vache and Lassolas; Basaltic eruptions; Clinopyroxene; Melt inclusions; Thermobarometry; Puys de La Vache et Lassolas; Eruptions basaltiques; Clinopyroxène; Inclusions magmatiques; Thermobarométrie; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Laki; Iceland
• Online Access: https://theses.hal.science/tel-01674222; https://theses.hal.science/tel-01674222/document; https://theses.hal.science/tel-01674222/file/HADDADI_2016CLF22745.pdf

Explosive basaltic eruptions are rare compared to effusive ones and the underlying physical mechanisms are poorly understood. The goal of this thesis is to study the causes of basaltic magma explosivity by characterizing the volcanic products of the subplinian eruption of trachy-basalt at the Puys de La Vache-Lassolas complex (Chaîne des Puys, France) and of phreatomagmatic and sub-plinian eruptions of tholeiitic magma at Grímsvötn volcano (Iceland). Minerals, matrix glasses and melt inclusions (Mis) were analysed with an electron microprobe to estimate volatile concentrations (initial and final), and pressure (P) and temperature (T) of crystallization using clinopyroxene-liquid thermobarometry. In addition, an experimental study was performed to better understand the limitations of clinopyroxeneliquid thermobarometry at moderate pressures and during magma ascent.Four eruptions were studied at Grímsvötn: two phreatomagmatic (AD1823 and AD2004) and two subplinian (AD1873 and AD2011). The subplinian eruptions have volatile concentrations higher than the phreatomagmatic ones, together with more efficient gas exsolution, leading to significantly higher atmospheric mass loading. Regardless of the eruptive regime, clinopyroxene-liquid (matrix glass or MI) equilibria in Grímsvötn magmas record the same depth of crystallization, namely ~15 km. This suggests that the shallow magma chamber of Grímsvötn plumbing system may only act as a reservoir in which gas exsolved from deeper origin is stored and accumulates between eruptions. The lower variability of clinopyroxene-MI equilibrium T in the 19th century eruptions, suggests important Grímsvötn magma system permeability following the Laki volcano-tectonic event end of 18th century. Average matrix glass-clinopyroxene equilibrium T decreases with time suggesting that Grímsvötn magma plumbing system as a whole may be slowly cooling over the last two centuries.Puys de La Vache-Lassolas products record a deeper magma contribution, from approximately 30 km depth. Initial ...