An integrated geochemical spatial and temporal survey of thermal springs to characterize the geothermal resource of a volcano (Piton des Neiges, Réunion Island)

2023

Article référencé dans le Web of Science WOS:001011061600001

Benard B., Famin V., Sanjuan B., Vimeux Françoise, Aunay B., Agrinier P., Lebeau G.

Applied Geochemistry, 2023, 154, 105689 [17 p.] ISSN 0883-2927

Geothermal exploration can be challenging in the absence of obvious surface indicators of a high enthalpy geothermal resource such as geysers, fumaroles or thermal springs with temperatures near 100°C This is the case at the Piton des Neiges volcano (Réunion Island), which displays evidence of hydrothermal activity mostly as thermal springs with temperatures not exceeding 50 °C, affected by mixing and reequilibration, and emerging in a complex geological framework, resulting from the polygenic history of this dormant volcano. Yet, these thermal springs keep a partial record of the reservoir geochemistry. Here, we propose an exploration method to set this thermal signature apart from the contribution of other processes and trace back the equilibrium conditions, enabling us to locate thermal fluid circulations, and evaluate their temperature and availability. We report its application at Piton des Neiges volcano. We led an extensive geochemical survey which nearly doubled the number of thermal springs reported on the volcano and dramatically extended the existing geochemical database in space and time. In tandem, we also monitored ?18O and ?D values in rainwaters and thermal springs over two years to compare their temporal variations. Our surveys show that the repartition of thermal springs is controlled by only one of the volcanic rift zones (the N30°E axis), which is thus identified as the heat source of hydrothermal circulations. This N30°E rift zone is also a preferential pathway for the degassing of mantellic CO2. In addition, the composition of thermal waters is influenced by syenite intrusions along the rim of the caldera, acting as drains for the uprise of hydrothermal waters. O, H and Sr isotopic signatures of springs show that the geothermal resource of Piton des Neiges is in fact made of two independent and unconnected hydrothermal systems on the northern and southern circular depressions of the volcano (the cirques of Salazie and Cilaos, respectively). ...

Hydrologie [062] ; Géophysique interne [066]

REUNION

Fonds IRD [F B010088127]

fdi:010088127