Gas Geochemistry at Grande Comore and Mayotte Volcanic Islands (Comoros Archipelago), Indian Ocean

Abstract

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The composition of gas emissions at Petite Terre (Mayotte, Comoros): inference on magmatic fingerprints

“…4 He/ 40 Ar * ratios at Petite Terre do not show systematic variations as a function of location or time. Liuzzo et al [2021] suggest that this homogeneous signature reflects that all bubbling spots are related to a single degassing source and pressure, likely related to magmas stored close to the mantle-crust underplating depth (15-20 km depth), as observed in other magmatic systems [e.g., Reunion, Boudoire et al, 2018]. This depth range corresponds to the shallower part of the magmatic plumbing system below Mayotte, where evolved basanitic magma differentiate to form phonolitic melts [Berthod et al, 2021a,b, Foix et al, 2021.…”

“…The Comoro Islands form an archipelago located in the Mozambique Channel between the east coast of Africa and the north-western coast of Madagascar. The formation of a huge submarine volcanic edifice since 2018, about 50 km offshore east of Mayotte, has focused the attention of the volcanological community with an increasing number of geophysical, petrological and geochemical studies [Bachèlery et al, 2019, Berthod et al, 2021a,b, Cesca et al, 2020, Lemoine et al, 2020, Liuzzo et al, 2021.…”

“…The islands of the Comoros archipelago are located within a particularly complex geodynamic region, whose volcanic and tectonic features are yet to be definitively constrained [Coffin et al, 1986, Gaina et al, 2013, Lemoine et al, 2020, Phethean, 2016. In this complex frame, only limited information exists on the signatures and sources of fluids and their potential link with the recent volcano-tectonic activity [Liuzzo et al, 2021].…”

Magmatic and phreatomagmatic contributions on the ash-dominated basaltic eruptions: Insights from the April and November–December 2005 paroxysmal events at Karthala volcano, Comoros

“…2). The absence of extended hydrothermal alteration on these nonjuvenile particles suggests that they are fragmented within the upper 1 km of the volcano (corresponding to the thick water-satured rock unit), as the hydrothermal system is located deeper and represent a weak activity in the Choungou-Chahalé crater area (Lénat et al, 1998;Savin et al, 2001Savin et al, , 2005Bernabeu et al, 2018;Liuzzo et al, 2021).…”

“…Furthermore, these newly emitted lavas represent a new thermolithological boundary within the crater floor, which can significantly drag hydrothermal fluids from the crater center towards peripheral areas (Bernabeu et al, 2018). Interestingly, the northern caldera lobe and the northern rift area hosts the strongest hydrothermal activity (fumaroles and soil degassing) of the volcanic system (Liuzzo et al, 2021) and produce dominantly effusive activities (e.g., 1965; 1972; 2007), whereas the hydrothermal activity is much weaker in the area of the central Choungou-Chahalé crater that feeds the most violent explosive activity (e.g., 1918; 1991; 2005). This geographical pattern suggests that, in the whole 2005-2007 Karthala activity, hydrothermal activity did not contribute to modulate the degree of explosivity.…”