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Séminaires internes 2021 - 2022

Contact : Jessica Flahaut (jessica.flahaut@univ-lorraine.fr)

Attention !!! A partir du lundi 27 Septembre 2021, les séminaires internes reprendront en présentiel dans l’amphi (avec jauge).

- 13 Septembre 2021 : Carolina Dantas Cardoso - Continuous isotopic tracing of crustal fluids transfer related to natural (seismic/volcanic) or anthropogenic hazards

Summary : Noble gases, unlike most stable isotopes or major elements used as geochemical tracers, are less susceptible to water/rock interactions and display widely variable ratios among the Earth reservoirs, making them good tracers of source and fluid interactions. 3He/4He ratios from groundwater in Italy are monitored by INGV through discrete sampling at seismically and volcanically active zones where they identified correlations between variations in 3He/4He ratios and earthquakes and eruptions. An uninterrupted sampling system has the potential to improve the monitoring at sites of interest, providing key information on processes of short timescales and their long-term geochemical backgrounds. Continuous sampling is possible using SPARTAH, an apparatus for automatic groundwater sampling. This project aims to comprehend the exchange and transfer of fluids to the surface in short timescales. With this knowledge, we hope to better constrain the sources and mechanisms involved in volcanic and seismogenic systems and potentially improve the forecasting of such hazards. Our current targeted areas are in northern (borehole HA-01) and southern (boreholes BA-01 and TH-13) Iceland. In the latter sites, monitoring is recent and we do not yet have any results. At HA-01, we started discrete weekly sampling in June 2020, shortly after an earthquake swarm, and continuous sampling with SPARTAH in September 2020. In addition to the monitoring, we surveyed the area around HA-01 for δ34S, δ18O, δ2H, δ13C, 3He/4He, 4He/20Ne, and major and trace elements to better characterize the region and interpret our monitoring data. In this presentation I’ll show you some of our preliminary results from Iceland, besides going briefly over some of our next projects.

- 27 Septembre 2021 : Maxime Piralla - Origin and chronology of the first solids in the early solar system

Summary : Chondrules, one of the first igneous objects formed in the protoplanetary disk, are powerful proxies of the processes that occurred during the formation of solar system. They appear to have formed during 4 Ma but the dynamic and the nature of the production processes (time, continuous or discrete, efficiency) and the importance of the recycled precursors on their isotopic compositions and formation ages are largely under-constrained. Besides, the genetic and temporal links between CAIs, AOAs and chondrules are as well poorly known. Knowing the duration and chronology of the chondrule-forming processes are crucial for our understanding of the dynamic of the protoplanetary disk. The objectives of my PhD are to couple high precision 26Al-26Mg dating of chondrules with in situ oxygen isotope analyses in order to constrain the timing, conditions and efficiency of primordial solid formation in the protoplanetary disk. During this presentation, I will show you a comprehensive study of chondrules from ordinary chondrites with petrographic and isotopic evidences that explain their formation processes. Meanwhile, we explore a new method for chondrule dating using spinel from various chondrite groups. This shows a clear dichotomy between CAIs/AOAs and chondrules ages, with chondrules seeming to be formed during a similar period.

- 11 Octobre 2021 : Marius Huber - Dynamics of giant landslides and their contribution to Himalayan erosion

Summary : Mountain ranges are affected by deep-seated landsliding which displays extremely variable sizes and rates of evolution, including rapidly failing rock slides and slow moving Deep-Seated Gravitational Slope Deformations (DSGSDs). The mechanics and kinetics of deep-seated landsliding remain relatively unknown, especially in the Himalayas, despite the fact that they represent a source of natural hazards and a major contribution to long term mountain erosion. The aims of the thesis is to investigate deep-seated landslides, whether they are very slow and of progressive nature, or fast moving and of catastrophic character, by using isotopic dating techniques and comparing their structural prerequisites with numerical models. This will lead to a better understanding of the causes and the evolution of deep-seated landslides, and will allow more insight into deep-seated landslide hazard, as well as into their consequences for erosion of mountain ranges.

- 25 Octobre 2021 : Yujin Jegal - Development of reference materials for in-situ Rb-Sr isotopic dating by laser ablation ICP-MS/MS and its application to W-Sn deposits in the French Massif Central

Summary : Rb-Sr dating techniques have been widely used as a geochronological tool to date and constrain the cooling history of geological events. However, in-situ dating using the 87 Rb- 87 Sr beta decay system is severely limited by the isobaric overlap of 87 Rb on 87 Sr. Recent developments in in-situ Rb-Sr isotopic techniques by laser ablation inductively coupled plasma mass spectrometry equipped with a collision/reaction cell (LA-ICPMS/MS) can resolve this problem, if appropriate reaction cell gases are used (O 2 , N 2 O and SF 6 ). In-situ Rb-Sr dating of minerals by LA-ICP-MS/MS requires calibration with well-certified matrix-matched reference materials with precisely known Rb/Sr ratios and Sr isotopic compositions. However, such well-characterized reference materials for in-situ Rb-Sr dating, in particular Rb-rich minerals such as micas, are currently limited.

In this study, reference materials suitable for in-situ Rb-Sr geochronology of high-Rb minerals (i.e., micas and feldspars) are firstly established and characterized. Four CRPG geostandards, phlogopite Mica-Mg, biotite Mica-Fe, glauconite GL-O and potash feldspar FK-N, were selected as potential mineral standards based on their broad compositional range, covering the compositional variation of micas and feldspars from granitic rocks. I will present the measured 87 Sr/ 86 Sr and 87 Rb/ 86 Sr values of the standards obtained by the isotope dilution method using multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) and thermal ionization mass spectrometry (TIMS) for Rb and Sr isotope measurements, respectively. The second goal is to examine the selected Rb-Sr standards using an Agilent 8900 ICP-MS/MS coupled with a LA system and to use them as reference materials for dating of unknown samples. Towards this goal, the in-situ Rb-Sr isochron ages of micas from W ± Sn deposits in the French Massif Central will be compared against their already known U- Pb ages (Harlaux et al., 2018b).

- 15 Novembre 2021 : Nicolas Schnuriger - Redox conditions of the formation of chondrules and their precursors

publié mercredi 31 août 2016