The island of La Réunion has been created by one of the most active volcanoes in the world. Its well-dated hotspot track leads unambiguously to the Deccan trapps of India, one of the largest flood basalt provinces on Earth, which erupted 65 Ma ago and seems to have had a massive impact on global climate and life at the time. But the genesis and the origin at depth of the mantle upwelling and of the hotspot are still very controversial.

We wish to establish the origin of the heat source that has been fueling this powerful hotspot: Is there a direct, isolated conduit into the deepest mantle, which sources its heat and material from near the core-mantle boundary? An isolated plume conduit connecting to the African superswell at mid-mantle depths? Or might the volcanism reflect merely an upper mantle feature? We also want to study the hotspot’s interaction with the neighboring ridges of the Indian Ocean. There is a long-standing hypothesis, not yet examined seismically, that channelized plume flow feeds the Central Indian Ridge at 1500 km distance. The aseismic Rodrigues Ridge is presumed to be the surface manifestation of this asthenospheric flow channel (though others conted that it is just a leaky transform fault). The goal of the RHUM-RUM experiment is to image a mantle plume – or lack of plume – from the surface down to the core-mantle boundary, and to understand these results in terms of material and heat flow. This comprises the vertically ascending flow in the plume conduit, as well as any lateral flow spreading into the asthenosphere of the western Indian Ocean. For this, we propose to use seismology and gravity methods.

 

This project is particularly ambitious through the scientific objectives we plan to tackle, through the number of broadband instrument we propose to deploy and through the size of the recording system. RHUM-RUM is the largest experiment so far aimed at imaging an oceanic mantle plume. It is fundamentally a German-French collaboration, allowing to tap into complementary scientific expertise, technical capabilities (land and ocean seismometers), and logistics (oceanic vessels). So, we can attain a critical mass which should enable to fulfill our scienitifc objectives of image the Reunion plume with the required resolution.

 

We propose to deploy 57 French and German ocean-bottom seismometers (OBS) over an area of 2000 km x 2000 km² centered on La Réunion Island. The OBS deployment will be augmented by 15 land seismographs in Madagascar, La Réunion and the Iles Eparses, and by 12 stations in the southern Seychelles proposed by our German partners. A data sharing agreement with U.S. collaborators will give us access to 33 additional stations in Madagascar, the Comores and Mozambique. A significant number of OBS placed along the Central and South West Indian Ridges are aimed at lower mantle imaging beneath the hotspot, but also provide independent opportunity for the study of these ridges and plume-ridge interactions.

 

 

 

 

 

 

 

For the end of the ANR program, a workshop has been organized from 28 aug to Sept. 3 s2016, in La Réunion, at the Cité du Volcan in Bourg Murat.

 50 scientists came to La Réunion, from France, Germany, UK, Norway and switzerland. The list of presentation that were presented during the workshop illustrates the works in progress that use the RHUM-RUM geophysical data.

 

 

 

 

Workshop RHUM-RUM

29 aout – 2 sept 2016

Bourg Murat, La Réunion

 

Scientific program

 

 

Villeneuve, N.; The Piton de la Fournaise recent volcanic activity

Ferrazzini, V.; Seismic activity of La Réunion island and the Catalogs and Bulletins from the OVPF

Peltier, A.; Contribution of GNSS to monitor and understand Piton de la Fournaise

BOUDOIRE, G., Y.-A. BRUGIER, A. DI MURO, G. WÖRNER, I. ARIENZO, N. METRICH, L. MICHON, M. PICHAVANT, V. ZANON,; Deep plumbing system and magma transfers at Piton de la Fournaise (La Réunion Island, Indian Ocean): A petrological and geochemical approach

Famin, V., Univ. Réunion; Magmatism and tectonics of Piton des Neiges volcano (La Réunion)

Michon, L., Univ. Réunion; Cenozoic volcanism of East Africa and western Indian Ocean: Mantle plumes and lithospheric deformation

Bissessur, D., J. Dyment & C. Deplus; New constraints on the age and structure of the oceanic lithosphere around the Mascarene Islands 

Deplus, C., D. Bissessur & J. Dyment; Past and present volcanism around La Reunion: insights from submarine volcanic structures

Gaina, C.; Oceanic crust formation in the Egeria Fracture Zone Complex

Dyment, J.,  C. Deplus & D. Bissessur ; Rise and fall of an Island: the Mauritius case

Simon Stähler, Mechita Schmidt-Aursch, Wolfgang Roeder; A self-noise model of OBS in the German DEPAS pool 

Scholz, J.-R. , G. Barruol, F.R. Fontaine; Determining OBS orientations on the ocean floor from P and Rayleigh-waves polarization

Crawford, W., Nicolas Leroy, Alessandro Mazzullo, Martha Deen and Eleonore Stutzmann; Removing the INSU-IPGP BBOBS glitches

Sarah Hable, Céline Hadziioannou, Karin Sigloch; Correction of clock errors in seismic data using ambient seismic noise

Tsekhmistrenko, M., K. Sigloch, K. Hosseini; Multi-Frequency measurements and common corrections of P waves on ocean bottom seismometers

Igel, H.; Towards a 7-C OBS system for seismology

Hable, S., Karin Sigloch, Valérie Ferrazzini;  Localization of widespread seismicity on La Réunion

Miller, S.,; Fluid-driven aftershocks and Omori’s Law

Crawford, W., Martha Deen, Eleonore Stutzmann; Seafloor compliance at the RHUM-RUM sites

Rindraharisaona, E.J. , F. Tilmann, X. Yuan, G. Rümpker, J. Giese, G. Rambolamanana; Crustal structure of southern Madagascar from receiver functions and ambient noise correlation: implications for the crustal evolution

Montagner, J.P.; What is a plate? LAB beneath oceanic and continental plates.

Singh,M., Georg Rümpker; Seismicity, seismic discontinuities and mantle anisotropy of Mauritius and Mascarene regions

Fontaine, F.R. , J.R. Scholz, G. Barruol, G. Rümpker, I. Wölbern; Lithosphere structure around La Réunion hotspot from receiver functions at few RHUM-RUM OBS stations. Preliminary results

Mazzullo, A., Eléonore Stutzmann; "Surface wave Tomography beneath La Réunion Island from RHUM-RUM experiment data"

Scholz, J.-R., G. Barruol, F.R. Fontaine; Anisotropy pattern in the Western Indian Ocean from SKS-splitting measurement  

Reiß, A-S,  Christine Thomas ; Upper mantle seismic discontinuities beneath the Indian Ocean 

Tsekhmistrenko, M., K. Sigloch, K. Hosseini, G. Barruol; Towards finite frequency tomography of mantle structure beneath the La Reunion hot spot

Hosseini, K., Karin Sigloch, Simon Staehler, Tarje Nissen-Meyer, Heiner Igel; Global multiple-frequency seismic tomography using teleseismic and core-diffracted body waves

Mahammadzaheri, A., Karin Sigloch; To what extent could a plume under La Réunion be tomographically visible?

Minakov, A., Carmen Gaina & Jan Inge Faleide; Crustal thickness in the west Indian Ocean using gravity inversion

Tommasi, A. Christel Tiberi; What can joint gravity and seismology inversion tell us about lithospheric structure?

Steinberger, B., Eva Bredow, René Gassmöller, Juliane Dannberg; Why there is a plume from the lowermost mantle rising under La Réunion (and not somewhere else)

Bredow, E., Bernhard Steinberger, René Gassmöller, Juliane Dannberg; Geodynamic models of the Réunion mantle plume

Agrusta,R., Andrea Tommasi, Diane Arcay, Alicia Gonzalez , Anne Davaille, Neil Ribe and Taras Gerya; Partial melting and small-scale convection in a plume-fed sublithospheric layer beneath fast-moving plates

Rümpker, G., Manav Singh; SplitRace : a semi automated tool for shear wave splitting

Farnetani, C.G., T. Duvernay, A. Limare, A.W. Hofmann; Dynamics of mantle plumes carrying viscous and/or denser heterogeneities

Werner, S.C., Steinberger, B. and Rolf, T.; Plumes on Other Planets

Stutzmann, E.; The composition of broadband noise in the indian ocean

Deen, M., Eleonore Stutzmann; Seismic noise recordings in the Indian Ocean: a focus on hum

Barruol, G., Céline Davy, Fabrice Fontaine, Eléonore Stutzmann, Karin Sigloch; Microseismic noise swell signature from the RHUM-RUM data

Andrianasolo, R., Gérard Rambolamanana, Jaona Andriamampandry; Malagasy seismic permanent stations, cyclon detectability and diurnal noise study

Snelling, B., Karin Sigloch, Guilhem Barruol, and Valérie Ferrazzini; Comparing hydroacoustic and T-phases from terrestrial and ocean-bottom recordings around La Réunion Island, Indian Ocean

Geay, B., Alexandre Bouillon, Richard Dreo, Guilhem Barruol, Fabrice Fontaine, Karin Sigloch and John Scholz; Ship noise in the RHUM-RUM data

Royer, JY, E Leroy, E Tsang-Hin-Sun, J. Bonnel & F. Samaran; Ambiant noise and blue whales in the austral Indian Ocean 

Wenner, M., Guilhem Barruol, Heiner Igel and Joachim Wassermann; Whale Detections from RHUM-RUM Ocean Bottom Seismic Observations

Gonzalez, A., Fabrice R. Fontaine, Arnaud Burtin, Guilhem Barruol, Alain Recking, Jean-Lambert Join, Eric Delcher; Monitoring sediment transport during cyclones from seismic noise in two rivers of La Réunion Island