The dynamics of the plumbing system and its consequence on the deformation of the volcanic edifice are two key issues for GéoSciences Réunion.
We consequently develop a multi-disciplinary approach combining geophysics, magmatology, geodesy and structrural geology.
Combined analysis of whole rocks, melt inclusions and matrix glasses of Piton de la Fournaise products unravel three stages of magmatic differentiation. The deepest (> 7.5 km depth) is dominated by clinopyroxene crystallization (Line 1). Above (2.5 km), fractionation is dominated by olivine, yielding steady state basalts at the top of the chamber and picrites at its bottom (Line 2). In shallow cooling dykes and subsurface pockets of magma, melts become more differentiated by clinopyroxene+plagioclase fractionation (Line 3). The shift from one differentiation line to the next is pressure dependent.
Famin et al. (2009)
One of the 8 crystal populations of olivine observed in the samples of the December 2005 eruption: Closed hopper-shaped olivine microcryst with three pairs of melt inclusions symmetrical about the centre of the grain.
Interpretative sketch of magma dynamics during the December 2005 eruption in the shallow reservoir of Piton de la Fournaise. Olivine and clinopyroxene microcrysts crystallize mostly at the cooler top margin of the chamber, and are then transported by convection to the hotter and more homogeneous interior, in which clinopyroxene is destabilized whereas olivine con- tinues to grow. Given the small size of the microcrysts, the convection cells are probably small-scale and short-lived, suggesting a low Rayleigh number barely above the critical value. Plagioclase microcrysts crystallize in the conduit during the ascent of the magma.
Welsch et al. (2009).
| ||Synthetic cross section and structural data from inner part of Piton des Neiges volcano, as observed in Mât River (outcrop M-2). Stereo diagrams are equal area, lower hemisphere. Magmatic layering and dikes are represented as poles in scatter and Kamb contour plots, and faults as striated planes. Orientations and plunges of principal stresses (five-, four- and three-legged stars represent σ1, σ2, and σ3, respectively) were computed from fault data using statistical method of Angelier (1984).|
Famin and Michon (2010)
3D view of the Fossa area showing the 2D high resolution electric resistivity tomography section performed in May 2002 by Revil et al. (2004). The Sectors 4 and 7 correspond to the 2002–2003 network of fractures in the Fossa area and to the increase of the soil concentrations of CO2 between the Sciara del Fuoco sector collapse boundary and the Pizzo crater, respectively. These sectors were already identified in May 2002, 7 months before the beginning of the 2002–2003 eruptive crisis, thanks to the inverted resistivity cross-sections. On these cross-sections, these sectors were associated with two major electric resistivity discontinuities. The labels 1 to 9 (in white) represent the different sectors of fluid flow identified along Profile A–A′.
Finizola et al. (2009)
Staff involved: Patrick Bachèlery, Marie Chaput, Vincent Famin, Anthony Finizola, Fabrice Fontaine, Laurent Michon, Nicolas Villeneuve.