Localization of magma injections, hydrothermal alteration, and deformation in a volcanic detachment (Piton des Neiges, La Réunion)

Origin and fate of hydrothermal fluids at Piton des Neiges volcano (Réunion Island): A geochemical and isotopic (O, H, C, Sr, Li, Cl) study of thermal springs

“…The spatial repartition of Group 2 springs suggests that the syenite dykes and/or the terminal caldera of the volcano may also act as hydrological barriers isolating the hydrothermal system. In addition, pore clogging by minerals of the phrenite-pumpellyite facies occurs in all the units older than 640 ka that constitute the basement of Piton des Neiges (Chevalier, 1979;Chovelon, 1968;Famin et al, 2016;Join et al, 2016). However, secondary mineral precipitation also occurs in Hawaii and the Azores (Cruz, 2003;Izquierdo, 2014;Schiffman et al, 2006) and thus hardly explains alone the isolation of the hydrothermal system from seawater in our case.…”

“…The hypovolcanic complex of Piton des Neiges is also affected by several phases of low-grade metamorphism and hydrothermal alteration (Chevalier, 1979;Rançon, 1985), resulting in the secondary precipitation of phrenite-pumpellyite facies minerals in rocks of the shield-building stage, followed by carbonate precipitation in differentiated rocks as well as in basic rocks (Famin et al, 2016). This long history of construction and destruction, intrusive activity and secondary mineral precipitation strongly affects the hydrogeology of Piton des Neiges, by limiting the escape of freshwater toward the sea and its downward infiltration in the lowermost, oldest and most impermeable rock units (Join et al, 2005;Violette et al, 1997).…”

“…Studies of secondary minerals at Piton des Neiges report the occurrence of abundant hydrothermal calcite precipitation in the porosity of basalts (Famin et al, 2016;Rançon, 1985), deposited by past episodes of magmatic carbon degassing. Such calcite may represent a significant carbon pool with a magmatic δ 13 C signature.…”

Layered gabbros and peridotites from Piton des Neiges volcano, La Réunion Island

“…Importantly, the current geometry, i.e. igneous bodies surmounted by sills and a breccia, results from one or several volcano flank destabilizations that likely occurred while the plutonic rocks were already solidified (Famin et al 2016). The main 6 features of the four sites are described below.…”

Multitechnique Geochronology of Intrusive and Explosive Activity on Piton des Neiges Volcano, Réunion Island

“…The top of this pluton is sheared and intruded by many sills (Berthod et al., 2016; Chaput et al., 2014; Famin & Michon, 2010), making any observation of the host rock contact impossible. The only chronological criteria available for this pluton is a greenschist to prehnite‐pumpellyite metamorphism (150°–240°C) (Famin et al., 2016), implying a cooling age older than the PN2 period (650–430 ka). The pluton is crosscut by a syenite laccolith, undeformed and unaltered (Berthod et al., 2020).…”