ISOTRAPIK Formation

This workshop is a national training action funded by the CNRS for students, technicians, engineers and researchers for the analysis of trace elements and isotopes by ICP-AES, HR- (LA) -ICP-MS, ICP-Q -MS, MC-TIMS, MC-ICP-MS, EA-IRMS, KIEL IV Carbonate-IRMS. The following modules will be covered: operation, maintenance, sample preparation, optimization, analysis, data processing.

More information at the following address: http://www.pso-brest.org/Actualites/ISOTRAPIK

Seminar of Mathieu Rosbapé

Interactions between magmatism and high temperature hydrothermalism under the ocean ridges: the example of Oman ophiolite

An important part of the chemical and thermal exchanges between the internal and external envelopes of the Earth (mantle, crust, hydrosphere) takes place at the level of the ocean ridges, in particular at the transition between mantle and oceanic crust (MTZ for Moho Transition Zone). MTZ acts as a reactive filter: the reactions between fluids and / or magmas resulting from the deep partial melting of the mantle and residual harzburgites lead to the resorption of the restitic orthopyroxenes and to the formation of a residue essentially formed of olivine, the dunites . This reaction is accompanied by an increase in porosity which favors the migration and extraction of magmas towards the crust.

Recent work on the study of Oman ophiolite has shown that high temperature hydrothermal processes, transient between anhydrous magmatism and late low temperature weathering, have affected MTZ and the upper part of the mantle section (Python et al., 2007, 2011; Akizawa et al., 2016; Rospabe et al., 2017). The occurrence of orthopyroxene and amphibole among the mineral impregnation phases within the MTZ (ie products of fractional crystallization from the interstitial magmas) provides information on the hydrated nature of the magma (s) enriched in silica. parent (s), contrasting with the MORB character expressed in crustal cumulates and mantle veins. The spatial distribution of these phases, more abundant near the base of the crust, suggests more crystallisation from a hybrid magma between ascending MORB and downstream hydrothermal front rather than a magma resulting from the partial melting of a deep hydrated source (Rospabé et al., 2017; Rospabe et al., 2018b). The correlation between spatial variation of the geochemical signatures and the presence of faults or synmagmatic fractures, which can be related to the process of accretion to the dorsal, provides information on the early establishment of these tectonic accidents, and on their important influence on structuration. Petrology and geochemistry of MTZ (Rospabé et al., submitted). The drilling of the CM1A and CM2B cores (400 + 300 m) through the Oman Oversight Oman Drilling Project (MTZ) aims at a sampling resolution never reached so far for this interface, as well as better quantification of elementary fluxes, in particular Cr, involved during such hybridization processes.

Thesis defense of David DELLONG

Active rifts and deep structure of the Eastern Sicilian margin

The Ionian basin in the central Mediterranean is exposed to several destructive earthquakes, sometimes accompanied by tsunamis, which were recorded in the past (Catania in 1693, Messina in 1908). However, the identification of faults and the tectonic regime related to these events is still debated in the scientific community. Moreover, from a geodynamic point of view, the importance of this basin lies in the fact that it shelters a subduction undergoing a “withdrawal of the diving plate” towards the Southeast since the last 35 Ma. This phenomenon is designated as responsible for the movements of large continental Mediterranean blocks such as the Corso-Sardinians (Corsica and Sardinia) and Calabro-Péloritain (Sicily and southern Italy). Mechanisms related to these large movements (over 700 km) are not fully understood and are the subject of much scientific debate. My thesis aims to identify some major flaws and improve the understanding of this subduction system and the East-Sicilian margin.

The DIONYSUS campaign, which took place in October 2014 aboard the German ship R / V Meteor, was a project led by four European institutes: Ifremer and CNRS-UBO (in France), Geomar (Germany) and INGV Rome (Italy) . This campaign collected wide-angle seismic data with 153 deployments of OBS (for Ocean Bottom Seismometer or Sea-bottom Seismometers), multitrace seismic reflection and bathymetry, along five profiles in the basin (see map). This type of data will make it possible to study the deep structure of the Ionian basin and the eastern Sicilian margin (up to 30 km deep). Two theses are currently in progress and model the OBS data of three profiles at Geomar and two in France between Ifremer and CNRS-UBO.

The velocity models obtained by modeling the two profiles (named DYP1 and DYP3) make it possible to identify several major structures. First of all, the probable position of a great fault called STEP (for Transform Edge Propagator) which is a great lithospheric tear fault, and which is related to the withdrawal of the diving plate. These models also allow us to image the deep structure of the oceanic cost of the basin as well as the Maltese Escarpment which is interpreted as an old transforming margin. This results are important for understanding the geodynamics of the basin.

Keywords

Active rifts, earthquakes, Seismic Wide-angle, Mediterranean, Italy, Sicily, Calabria, Eastern-Sicilian Margin, Geodynamics, Deep Structure, Crustal

Thesis Director (s): Frauke Klingelhoefer (Ifremer) & M-A Gutscher (LGO)

Sémardi de Jean Lecoulant

Modélisation 3D des ondes acoustiques (ondes T) générées par les séismes sous-marins

Les dorsales médio-océaniques étant généralement éloignées des réseaux sismologiques à terre, leur activité sismique de faible intensité et les mécanismes associés restent mal connus. Le déploiement d’hydrophones pour enregistrer les ondes hydro-acoustiques générées par les séismes sous-marins – dites ondes T – permet d’exploiter les excellentes propriétés acoustiques de l’océan, qui pallient l’atténuation rapide des ondes sismiques dans la croûte. Pour mieux comprendre la production d’ondes T, nous utilisons un code 3D  – SPECFEM3D –, qui modélise conjointement la propagation des ondes sismiques dans la croûte et celle des ondes sonores dans l’océan. Les résultats présentés porteront sur la propagation des ondes T, les effets 3D à la génération et les conséquences de ces effets 3D sur la localisation de l’épicentre grâce à un réseau d’hydrophones.

3D-modeling of the acoustic waves (T-waves) generated by submarines earthquakes

Mid-oceanic ridges are generally remote from the seismographers networks deployed on land, hence their low-amplitude seismic activity and the associated focal mechanisms remain poorly known. Deploying hydrophone to record hydro-acoustic waves generated by sub-marine earthquake – T-waves – make possible to exploit the excellent acoustic property of the ocean, overcoming the fast attenuation of seismic waves within the crust. To better understand the T-waves emission, we use a 3D-code – SPECFEM3D –, jointly modeling the propagation of seismic waves in the crust and the one of acoustic waves in the ocean. The presented results will deal with the T-waves propagation, the generation 3D-effects and their consequences on the localisation of the epicenter by using a hydrophones network.

voir la vidéo

Sémardi de présentation des nouveaux doctorants 2018/2019

Claire Charles
Etudes géochimiques et minéralogiques des encroutements ferromanganésifères en vue de reconstructions paléocéanographiques et paléogéodynamiques du canal du Mozambique.

voir la vidéo

Vincent Coussin
Transect Méditerranée occidentale-orientale : palynologie marine et gradients climatiques (continentaux et hydrologiques) au cours de l’Holocène.

voir la vidéo