The Shallow Plumbing System of Piton de la Fournaise Volcano (La Réunion island, Indian Ocean) Revealed by the Major 2007 Caldera Forming Eruption (Invited)

The 2007 eruption represents a major event in the recent history of Piton de la Fournaise volcano because it produced: i) the most voluminous lava field (at least 0.21 km3), ii) the most intense lava fountaining activity (>200 m high), iii) the largest SO2 plume (>230 kt), iv) the largest summit collapse (1 km wide x 0.34 km deep) and v) the main flank slip event (up to 1.4 m eastwards) ever documented at PdF. The bulk magma volume extruded during the 2007 eruptive sequence is similar to that emitted during the entire 1998-2006 period. As a whole, the volume of magma emitted during the whole 1998-2007 activity cycle is remarkably close to that estimated (~0.35 km3) for the shallow plumbing system of Piton de la Fournaise. The 2007 eruptive sequence consisted of three successive phases (February, March and April). The main caldera forming phase of April ended a 9 years long period (1998-2007) of continuous edifice inflation and frequent eruptive activity (3 eruptions per year on average). On the contrary, post-2007 activity punctuates a trend of continuous deflation and consists of small-volume summit eruptions of moderate/low MgO magmas and frequent shallow magma intrusions. The 2007 lavas and pyroclasts cover the complete range of textures and crystal content an composition typically found in PdF products. The broad range of textures and the large volumes of pyroclasts, lava and gas emitted in 2007 provide an unique and exceptional record of the time-integrated evolution of PdF magma, and represent an unique opportunity to image the volcano plumbing system and bring new constraints on the processes controlling its magmatic and volatile budget. We here address these issues by using an unprecedented geochemical dataset (major, volatile and trace elements, Sr-Nd isotopes) on bulk rocks, minerals, glass inclusions and glass matrices from a very detailed sample set, representative of the time evolution of extruded magma during the entire 2007 eruptive sequence.