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![Map of major geographic features of the study area and data acquired during the 2020-2021 SISMAORE cruise. SBP, sub-bottom profiler lines; thin lines, SISRAP, 48-channel seismic reflection; Multichannel seismic (MCS) data, 960-channel seismic reflection Masquelet et al. [2022]; OBS, ocean bottom seismometer. Multibeam echosounder system (MBES) and water column acoustic data were obtained along all black lines Thinon et al. [2020b]. Volcanic islands: GC, Grande-Comore; Mo, Mohéli; A, Anjouan; Ma, Mayotte. Major seamounts and chains: V, Vailheu; J, Jumelles; Z, Zélée Bank; G, Geyser Bank; L, Leven Bank; C, Cordelière Bank. White stars: K, Karthala volcano; FMV, Fani Maore volcano; FaC, Fer à Cheval volcanic complex [Feuillet et al., 2021]. Detailed bathymetry from the compilation of Tzevahirtzian et al. [2021] (surveys listed in references and in Counts et al. [2018]) superimposed on GEBCO regional low-resolution bathymetry [Weatherall et al., 2015]. White outlines correspond to other figures in this paper.](profile/Isabelle-Thinon/publication/366422310/figure/fig2/AS:11431281111168313@1672921710595/Map-of-major-geographic-features-of-the-study-area-and-data-acquired-during-the-2020-2021.png)
Map of major geographic features of the study area and data acquired during the 2020-2021 SISMAORE cruise. SBP, sub-bottom profiler lines; thin lines, SISRAP, 48-channel seismic reflection; Multichannel seismic (MCS) data, 960-channel seismic reflection Masquelet et al. [2022]; OBS, ocean bottom seismometer. Multibeam echosounder system (MBES) and water column acoustic data were obtained along all black lines Thinon et al. [2020b]. Volcanic islands: GC, Grande-Comore; Mo, Mohéli; A, Anjouan; Ma, Mayotte. Major seamounts and chains: V, Vailheu; J, Jumelles; Z, Zélée Bank; G, Geyser Bank; L, Leven Bank; C, Cordelière Bank. White stars: K, Karthala volcano; FMV, Fani Maore volcano; FaC, Fer à Cheval volcanic complex [Feuillet et al., 2021]. Detailed bathymetry from the compilation of Tzevahirtzian et al. [2021] (surveys listed in references and in Counts et al. [2018]) superimposed on GEBCO regional low-resolution bathymetry [Weatherall et al., 2015]. White outlines correspond to other figures in this paper.
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Geophysical and geological data from the North Mozambique Channel acquired during the 2020–2021 SISMAORE oceanographic cruise reveal a corridor of recent volcanic and tectonic features 200 km wide and 600 km long within and north of Comoros Archipelago. Here we identify and describe two major submarine tectono-volcanic fields: the N’Droundé provinc...
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... work has focused on the Comoro Islands, and few papers have treated the offshore parts of the Archipelago (Figure 2). Using bathymetric data, Audru et al. [2006] and Tzevahirtzian et al. [2021] provide overviews of the volcanic structures and slope instabilities on the flanks of the islands. ...
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... Comoros Archipelago includes the four main islands, Grande-Comore, Mohéli, Anjouan and Mayotte, as well as submerged features including the Jumelles seamounts, Vailheu seamount and the Zélée-Geyser banks [e.g., Tzevahirtzian et al., 2021; Figure 2]. Seismic stratigraphy [Leroux et al., 2020] indicates that the main volcanic phase of Mayotte (late Paleogene to Neogene) is much younger than Zélée-Geyser banks (Cretaceous-Paleogene transition), which in turn are younger than the Glorieuses seamounts (Late Cretaceous). ...
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... the northern slope off Mayotte, several small volcanic edifices are part of a longer line of volcanoes trending N140°E from Anjouan to Petite-Terre [ Audru et al., 2006]. On the seafloor east of Mayotte, the MAYOBS monitoring cruises [Rinnert et al., 2019, REVOSIMA newsletter, 2021 during the 2018-2021 Mayotte seismo-volcanic crisis have documented the N110°E trending Eastern Volcanic Chain of Mayotte (EVCM; Figure 2), a line of numerous volcanic structures with a new active volcanic edifice 800 m high and 5 km in diameter at its tip [Berthod et al., 2021a,b, Cesca et al., 2020, Lemoine et al., 2020. This active submarine volcano is called Fani Maor'e volcano (name submitted to the UNESCO's International Marine Chart Commission, Figure 2). ...
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... the seafloor east of Mayotte, the MAYOBS monitoring cruises [Rinnert et al., 2019, REVOSIMA newsletter, 2021 during the 2018-2021 Mayotte seismo-volcanic crisis have documented the N110°E trending Eastern Volcanic Chain of Mayotte (EVCM; Figure 2), a line of numerous volcanic structures with a new active volcanic edifice 800 m high and 5 km in diameter at its tip [Berthod et al., 2021a,b, Cesca et al., 2020, Lemoine et al., 2020. This active submarine volcano is called Fani Maor'e volcano (name submitted to the UNESCO's International Marine Chart Commission, Figure 2). ...
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... analogue modelling of Montanari et al. [2017] shows that the growth of dome-shaped forced folds produces tensional and compressional deformation (normal and reverse faults) in the sedimentary cover. Some of the dome-shaped forced folds in the Mwezi province are accompanied by faults with sub-vertical offsets reaching 10 m (Figure 7a2-a4, b). The disruption of seismic signals under and over the sills may result from the presence of overlying lava flows (acoustic masking) or fluid migration pathways (chimneys) [Masquelet et al., 2022, and references therein]. ...
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... are as long as 10 km and have vertical offsets of up to 10 m (see F 1 , F 2 , F 3 on Figures 5d and 7a3). Some of these escarpments consist of discontinuous, slightly shifted segments (Supplementary Figure S2). Some connect seamounts or domes, and some cut across domes producing vertical offsets of 10-20 m (see F 1 cutting domes D 3 and D 4 on Figure 5d; Supplementary Figure S2). ...
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... of these escarpments consist of discontinuous, slightly shifted segments (Supplementary Figure S2). Some connect seamounts or domes, and some cut across domes producing vertical offsets of 10-20 m (see F 1 cutting domes D 3 and D 4 on Figure 5d; Supplementary Figure S2). We interpret these escarpments as faults with sub-vertical components. ...
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... sets of faults and volcanic structures, both too recent to be covered by sediments, appear to be coeval as they crosscut each other in many cases. Some of the faults cut the surface of the domeshaped forced folds or connect two major structures (e.g., fault Lf1 in Figure 5e, Supplementary Figure S2). They can form graben systems (e.g., Figures 5d, 7a2 7a4) or lines of offset segments (e.g., Figure 6c,d). ...
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... can form graben systems (e.g., Figures 5d, 7a2 7a4) or lines of offset segments (e.g., Figure 6c,d). Most of the faults show sub-vertical offsets reaching 20 m, often with a normal component (Figure 7, Supplementary Figure S2). Strike-slip motion could exist, but is not easy to identify in the seismic profiles. ...
Citations
... Mayotte is the easternmost island of the Comoros volcanic archipelago at the northern entrance of the Mozambique Channel, 300 km west of Madagascar (Fig. 1). The geodynamic context of the Comoros volcanic archipelago is still debated, and the islands either originated from a hotspot track (Emerick and Duncan 1982), a deep lithospheric fault (Nougier et al. 1986;Upton 1982), or an immature plate boundary (Famin et al. 2020;Michon et al. 2022;Stamps et al. 2021;Thinon et al. 2023). The archipelago is composed of four islands (from west to east: Grande Comore, Moheli, Anjouan, and Mayotte). ...
We studied four Quaternary volcanic phonolitic explosive edifices on Petite-Terre Island (Mayotte, Comoros Archipelago, Western Indian Ocean) to quantify magma fragmentation processes and eruptive dynamics. Petite-Terre explosive volcanism is the westernmost subaerial expression of a 60-km-long volcanic chain, whose eastern tip was the site of the 2018–2020 submarine eruption of the new Fani Maoré volcano. The persistence of deep seismic activity and magmatic degassing along the volcanic chain poses the question of a possible reactivation on land. Through geomorphology, stratigraphy, grain size, and componentry data, we show that Petite-Terre “maars” are actually tuff rings and tuff cones likely formed by several closely spaced eruptions. The eruptive sequences of each edifice are composed of thin (cm–dm), coarse, lithic-poor pumice fallout layers containing abundant ballistic clasts, and fine ash-rich deposits mostly emplaced by dilute pyroclastic density currents (PDCs). Deposits are composed of vesiculated, juvenile fragments (pumice clasts, dense clasts, and obsidian), and non-juvenile clasts (from older mafic scoria cones, coral reef, the volcanic shield of Mayotte, as well as occasional mantle xenoliths). We conclude that phonolitic magma ascended directly and rapidly from depth (around 17 km) and experienced a first, purely magmatic fragmentation, at depth (≈ 1 km in depth). The fragmented pyroclasts then underwent a second shallower hydromagmatic fragmentation when they interacted with water, producing fine ash and building the tuff rings and tuff cones.
... Lithospheric-scale fault zones likely affect the mantle, given Mayotte's location on a plate boundary. (Famin et al., 2020;Thinon et al., 2022). Besides, the proximal cluster lies beneath volcanic structures on the seafloor . ...
... For instance, in the Azores (Fig. 2) a plume is involved but it rises beneath a complex plate junction involving the Mid-Atlantic Ridge and the Terceira Rift (Fernandes et al., 2006;Georgen and Sankar, 2010). Magmatism at the Comoros (Fig. 2) is controlled by a fault that connects to the East African Rift system (Michon, 2016;Famin et al., 2020;Michon et al., 2022;Thinon et al., 2022). Volcanism in the Gulf of Guinea (Fig. 2), and on nearby mainland Africa, has taken place at multiple locations, but there is no age-progression (Njome and de Wit, 2014). ...
Mantle-plume hotspot islands are a common focus of biogeographical studies, and models for the growth of their biodiversity often incorporate aspects of their physical evolution. The ontogenetic pathways of such islands have generally been perceived as simple, comprising successive episodes of emergence, growth, peak size, reduction and elimination. In this paper, we improve knowledge of island development by examining key physical data from 60 islands at eight archipelagoes in equatorial to mid-latitude regions of the Atlantic, Indian and Pacific oceans. Such landmasses achieve their maximum sizes within 200-500 kyrs. However, island longevity varies by up to a factor of 5 and is strongly controlled by the speed of the associated tectonic plate as it moves over the narrow, thermally-elevated conduit where volcanism is focused. At moderate to high speeds (40-90 mm/year; e.g., Gal apagos, Hawaii), lifetimes are no more than 4-6 Myrs. In contrast, the oldest landmasses (in the Cabo Verde, Canary, and Mascarene archipelagoes) are built upon slow-travelling plates (<20 mm/year) and date from the Miocene. Notably, Fuerteventura in the Canary Islands, where the rate is c. 2.5 mm/year, has existed since 23 Ma. Two processes likely sustain the sub-aerial elevation of these massifs: heat from the plume expands the underlying lithosphere thus increasing its buoyancy, which in turn inhibits cooling-contraction subsidence; protracted magmatic activity counteracts denudation. Furthermore, the Cabo Verde and the Canary archipelagoes sit within dry climatic regions, which likely reduced erosion and mass-wasting. Consequently, two ontogenetic models are presented, one for the edifices on the intermediate-and fast-moving plates, and a second for the constructions on the slow-moving plates. The development path for the former is similar to the schema that is commonly envisaged (see above) and takes place over c. 5 Myrs, whereas the one for the latter is rather different and involves quasi-continuous surface renewal plus the maintenance of elevation that lasts for c. 10-25 Myrs. The new information should permit a fuller understanding of how a hotspot island's physical development shapes its biota and inform the formulation of related theoretical models.
... The Comoros archipelago, located in the northern Mozambique channel (Fig. 1a) has regained attention from the scientific community since 2018 due to the birth of a fast-building submarine volcanic edifice, 50 km east of Mayotte, Fani Maoré volcano (Lemoine et al., 2020;Feuillet et al., 2021;Berthod et al., 2021a). Marine geophysical surveys have since revealed that the archipelago is only the emerged portion of a much wider province of volcanic ridges and seamounts extending north and east of the islands (Tzevahirtzian et al., 2021;Thinon et al., 2022). The origin of volcanism in the Comoros archipelago remains enigmatic in many aspects since none of the proposed interpretations can explain all the observations. ...
... Bachèlery and Hémond, 2016). The HIMU signature is sought to be introduced in the Comorian mantle reservoir through Rinnert et al., 2019;Ifremer Geo-ocean, 2022;Thinon et al., 2022;Berthod et al., 2021b, and GEBCO data), GNSS plate motions in a no-net rotation (NNR) framework (King et al., 2019). b-Topographic and bathymetric map of Mohéli and the Chistwani ridge showing the location of analyzed samples. ...
... Our results imply that at least two additional flank collapses occurred during the same time interval nearby on Mohéli, with the possibility that all these events might be chronologically or even genetically related. Destabilizations have also been evidenced on the slopes of Mayotte (Audru et al., 2006;Thinon et al., 2022), but their timing relative to Mohéli's and Anjouan's events is yet to be established. ...
The Comoros archipelago has attracted renewed attention since 2018 due to the submarine volcano growing east of the island of Mayotte and the associated ongoing seismic crisis. However, the origin of Comorian magmatism remains controversial, as it is either interpreted as related to a hotspot trail, to a fracture zone, or to a plate boundary. Lying in the central part of the archipelago, Anjouan is a key island to better understand the relationship between volcanism and geodynamics. Together with a careful selection of published whole-rock K–Ar ages, our new set of 13 groundmass K–Ar ages on lava flows and one radiocarbon age on a charcoal from a strombolian deposit, allow us to reassess the volcano-tectonic evolution of Anjouan Island. New groundmass K–Ar ages lie within the last 1 Ma, i.e. from 899 ± 14 to 11 ± 1 ka. They suggest that most of the subaerial volcanism in Anjouan is much younger than previously inferred, and occurred as pulses at 900–750 ka, perhaps 530 ka, 230–290 ka, and since 60 ka, with erosional periods in between. Among our new data, one 14C age of 7513–7089 yrs calBCE (9.3 ± 0.2 ka) and five K–Ar ages younger than 60 ka show that recent volcanism occurred in Anjouan. Moreover, the concentration of eruptive vents along a N150° alignment, parallel to the maximum horizontal stress, suggests a strong link between regional tectonics and volcanism. Considering the presence of active volcanoes on both the western and eastern extremities of the Comoros archipelago, our discovery of Holocene activity on Anjouan provides strong arguments against a chronological progression of volcanism along the archipelago, and therefore contradicts the hotspot hypothesis for the origin of volcanism.
Finally, this study provides a robust geochronological timeframe of the different volcanic stages of Anjouan. It demonstrates that Anjouan is an active island and suggests that volcanism and tectonics can both resume at any time.
... The source of this magma is evaluated to be located at 30-50 km depth into the underlying mantle, with the potential involvement of an intermediate magma chamber at ~17 km depth (Berthod et al., 2021b). This new volcano is an addition to the East-Mayotte Volcanic Chain (EVCM, Thinon et al., 2022), characterized by the emission of magmas falling along an alkaline basanite-to-phonolite magmatic differentiation trend. This volcanic chain is quite complex and characterized by large effusive lava flow fields, and by the presence of more explosive volcanoes ( Fig. 1) (Puzenat et al., 2022;Gurioli et al., 2023;. ...
Following an unprecedented seismic activity that started in May 2018, a new volcanic edifice, now called Fani
Maoré, was constructed on the ocean floor 50 km east of the island of Mayotte (Indian Ocean). This volcano is the
latest addition to a volcanic chain characterized by an alkaline basanite-to-phonolite magmatic differentiation
trend. Here, we performed viscosity measurements on five silicate melts representative of the East-Mayotte Volcanic
Chain compositional trend: two basanites from Fani Maoré, one tephriphonolite and two phonolites from
different parts of the volcanic chain. A concentric cylinder viscometer was employed at super-liquidus conditions
between 1500 K and 1855 K and a creep apparatus was used for measuring the viscosity of the undercooled melts
close to the glass transition temperature in the air. At super-liquidus temperatures, basanites have the lowest viscosity
(0.11–0.34 to 0.99–1.16 log10 Pa⸱s), phonolites the highest (1.75–1.91 to 3.10–3.89 log10 Pa⸱s), while the
viscosity of the tephriphonolite falls in between (0.89–1.97 log10 Pa⸱s). Near the glass transition, viscosity measurements
were performed for one phonolite melt because obtaining pure glass samples for the basanite and
tephriphonolite compositions was unsuccessful. This is due to the formation of nanolites upon quench as evidenced
by Raman spectroscopy. The phonolite viscosity ranges from of 10.19 log10 Pa⸱s at 1058 K to 12.30 log10
Pa⸱s at 986 K. Comparison with existing empirical models reveals an underestimation of 1.2 to 2.0 log units at super-
liquidus and undercooled temperatures, respectively, for the phonolite. This emphasizes (i) the lack of data
falling along the alkaline basanite-to-phonolite magmatic differentiation trend to calibrate empirical models, and
(ii) the complexity of modeling viscosity variations as a function of temperature and chemical composition for alkaline
compositions. The new measurements indicate that, at eruptive temperatures between 1050 °C and
1150 °C (1323–1423 K), the oxidized, anhydrous, crystal-free and bubble-free basanite melt have a viscosity
around 2.6 log10 Pa⸱s. In contrast, the anhydrous phonolite crystal- and bubble-free melt would have a viscosity
around 6–10 log10 Pa⸱s at expected eruptive temperatures, from 800 to 1000 °C (1073–1273 K). Considering that
both basanite and phonolite lavas from the Mayotte submarine volcanic chain contain <6% crystals and a significant
amount of water (1-2.3 wt% and 0.8-1.2 wt%, respectively), such viscosity values are probably upper limits.
The new viscosity measurements are essential to define eruptive models and to better understand the storage
and transport dynamics of Comoros Archipelago magmas, and of alkaline magmas in general, from the source to
the surface.
... from oceanic cruises such as SIS-MAORE (doi:10.17600/18001331), and from the now regular MAYOBS surveys (doi:10.18142/291). In Thinon et al. [2022] for instance, extension of the submarine volcanism in the northern Mozambique channel is evidenced, and the regional geodynamics is investigated by means of marine geophysics. This first part also questions the nature of the lithosphere beneath the Comoros archipelago, by probing its thermal state from literature and newly published heat flow measurements and its structure from teleseismic receiver functions [Dofal et al., 2022]. ...
We shed light on the nature and structure of the crust surrounding the Comoros Archipelago, western Indian Ocean, offering insights into the region's geological history and volcanic island formation. Our comprehensive study encompasses the acquisition of new, deeply penetrating seismic data from the SISMAORE cruise (refraction and reflection seismic), and the subsequent analysis of the characteristics and structure of the crust surrounding the Comoros Archipelago. Both the reflection seismic imaging and the velocity structure using ocean bottom seismometers indicate that the crust of the Comoros Basin exhibits oceanic characteristics, thus resolving previous controversies about its nature. The thickness of the oceanic crust ranges from 5.8 to 6.6 km in the north of the archipelago to 6–7.2 km within the Comoros Basin. The estimated roughness of the top basement in the Comoros Basin ranges from 110 to 200 m values typical of intermediate to slow spreading ridges, such as the extinct spreading centre in the West Somali Basin.
The unloaded basement depth of the Comoros Basin closely matches the expected water-loaded subsidence for a Cretaceous or Jurassic oceanic lithosphere. In contrast, the West Somali Basin to the north of the Comoros Archipelago has shallower basement depths, potentially linked to recent volcanic activity along the archipelago.
We propose that the pre-existing oceanic fracture zones in the West Somali Basin underwent reactivation, first during the Turonian period and later during the Late Eocene. These reactivated fracture zones may have acted as preferred pathways for the emplacement of the volcanic islands of the Comoros Archipelago. The EW trend of the archipelago appears to follow a marked change in the direction of these reactivated fracture zones, suggesting that the associated lithospheric weakening likely played a critical role in facilitating the formation of the Comoros Archipelago.
During the last 10 kyr, significant subsidence and uplift occurred on Mayotte Island in the Comoros archipelago (Indian Ocean), but the role of volcanic processes in Holocene vertical movements has been neglected in the research so far. Here, we show that an abrupt subsidence of 6–10 m occurred between 9.4 and 10 kyr ago, followed by an uplift of the same amplitude at a rate of 9 mm/yr from 8.1 to 7 kyr ago. A comparison of the relative sea level of Mayotte and a reference sea level curve for the global ocean has been conducted using a modeling approach. This shows that an increasing and decreasing pressure at depth, equivalent to the process caused by a deep magma reservoir (50–70 km), was responsible for ~6–10 m subsidence and 6–10 m uplift, whereas loading by new volcanic edifices caused subsidence during the last few thousand years. Surface movements and deep pressure variations may be caused by pulses from the deep mantle, related to superplume activity, but uncertainties and unknowns about these phenomena are still present and further studies are needed. A better understanding of the volcano-tectonic cycle may improve assessments of volcanic hazards.
We describe four Quaternary volcanic phonolitic explosive edifices containing mantle xenoliths on Petite-Terre Island (Mayotte, Comoros Archipelago, Western Indian Ocean) to quantifying magma fragmentation processes and eruptive dynamics. Petite-Terre explosive volcanism is the westernmost subaerial expression of a 60 km volcanic chain, whose eastern submarine tip has been the site of the 2018–2021 sub-marine eruption which saw the birth of a new volcano, Fani Maoré. The scattered recent volcanic activity and the persistence of deep seismic activity along the volcanic chain requires to constrain the origin of past activity as a proxy of possible future volcanic activity on land. Through geomorphology, stratigraphy, grain size and componentry data we show that Petite-Terre tuff rings and tuff cones are likely formed by several closely spaced eruptions forming a monogenetic volcanic complex. The eruptive sequences are composed of few, relatively thin (cm-dm) coarse and lithic rich pumice fallout layers containing abundant ballistic clasts, and fine-ash rich deposits mostly emplaced by dilute pyroclastic density current (PDCs). All deposits are dominated by vesiculated, juvenile (pumice clasts, dense clasts, and obsidian) and non-juvenile clasts from older mafic scoria cones, coral reef and the volcanic shield of Mayotte as well as mantle xenoliths. We conclude that phonolitic magma ascended directly and rapidly from the mantle and first experienced a purely magmatic fragmentation at depth (≈ 1 km deep). The fragmented pyroclasts underwent a second shallower hydromagmatic, fragmentation where they interacted with liquid water, producing fine ash and building the tuff ring and tuff cone morphologies.
