Conférence GM & ED Gaïa :

Tracing rock provenance: how to analyse rocks/stones in a non-destructive, portable but quantitative way?

at 14:00 amphi 23.01 campus Triolet – Université de Montpellier

presented by Antoine TRIANTAFYLLOU (Laboratoire de Géologie de Lyon )

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One of the major challenges in geosciences and more specifically in geoarchaeology is to provide a precise fingerprint of rocks or stones and identify their provenance, linking them to a given source (quarry or an erosional site, etc.). Combining multiple analytical methods and diversifying discriminant proxies is the key to improve the distinction of sourcing regions with a higher spatial resolution. Doing these analyses directly in the field can be very useful or mandatory. It is trivial for geoarchaeology studies for which chemical analyses have to be non-destructive and on site. For geology projects, having a portable lab can guide our sampling strategy and/or give us a more continuous records on geological objects. Anyway, here, I will present some methods and nice results we had, using multiple handheld analytical tools from the FAIRE platform I’m overseeing, including portable X-ray fluorescence spectrometer (pXRF), portable Magnetic Susceptibilimeter, portable Laser Induced Breakdown Spectroscopy (pLIBS), and portable Raman spectrometer. I will illustrate some of their advantages/limitations and few applications via different ongoing research projects in geoarchaeology in Crete, Corsica, Rome.

 

Antoine Triantafyllou is Assistant Prof. at the Laboratoire de Géologie de Lyon since 2020. He did his PhD at the University of Nantes and the University of Mons in Belgium, and several post-docs at the ALC in Arizona, the GTime laboratory at the University of Brussels and the Geopetro lab at the university of Liège.

 

 

 

 

Conférence GM & ED Gaïa :

Deformation and hydration state of the mantle wedge corner in subduction zones

presented by Ikuko WADA (University of Minnesota, USA)

at 11:00 amphi 23.01 campus Triolet – Université de Montpellier

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The physical state of the mantle wedge corner in subduction zones affects a range of important processes, such as megathrust earthquakes, tremor and slow slip, and deformation of the overriding forearc lithosphere. The deformation condition of the mantle wedge corner has been inferred from shear wave splitting (SWS) observations, but their interpretation depends on the crystal-preferred orientation (CPO) of minerals in the wedge corner. Further, its physical properties are impacted by the hydration of the mantle rock peridotite into serpentinite. Serpentinization causes density and strength reduction and volume increase of the mantle rock, and its spatial extent depends on fracture networks, which in turn depend on tectonic and reaction-induced stresses. Our project aims to provide a better understanding of the deformation and serpentinization of the mantle wedge corner by addressing (1) the CPO patterns in the mantle wedge corner and their impact on SWS and (2) the effects of tectonic and reaction-induced stresses on fracture formation and the spatial extent of serpentinization in the mantle wedge corner.

 

B.Sc. and Ph.D. from the University of Victoria, Canada; Postdoc at the Woods Hole Oceanographic Institution, MA, and Virginia Tech, VA, USA; Assistant professor at Tohoku University, Japan; Currently Associate professor at the University of Minnesota, USA. The main research field is subduction zone geodynamics. Research topics include heat transfer, mantle flow, lithospheric deformation, and fluid migration.

 

 

 

Conférence GM & ED Gaïa :
Potential, premises, and pitfalls of illite geochronology

by Mathias HUECK

University of São Paulo (Brazil) & University of Bochum (Germany)

at 11:00 amphi 23.01 campus Triolet – Université de Montpellier

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The Ar/Ar and K-Ar dating of illite and clay-sized white mica is a powerful geochronological tool that can provide reliable ages for diverse geological processes such as burial- and fluid-controlled diagenesis and weathering, to low-temperature regional metamorphism and folding, as well as fault activity in the brittle and ductile-brittle regimes. Because of its versatility, it has become an established method that has been used in hundreds of studies around the world, offering valuable insights into the evolution of sedimentary basins and the interplay between deformation and fluid flow in the upper crust. Nonetheless, the interpretation of illite dates is not straightforward, as individual results are often scattered, both in systematic sample sets and in grain-size separated aliquots from the same sample. Hence, special strategies have to be devised for correctly interpreting this kind of data. The talk will present both sides of the equation: the potential and flexibility of illite geochronology in addressing different geological questions, as well as the precautions that should be made when interpreting the resulting ages.

 

Mathias Hueck is a graduate of the University of São Paulo (Brazil), a PhD student at the University of Göttingen (Germany), a post-doctoral fellow at the University of São Paulo, and currently a research associate at the University of Bochum (Germany). His main field of research is the interaction between tectonics, geochronology and petrology, and its application to the reconstruction of regional geological evolutions and the calibration of tectonic processes.

 

 

Conférence GM & ED Gaïa :
Secrets of the sunken basilica on the activity of Middle branch of the North Anatolian Fault

by Julia de SIGOYER

ISTerre, Grenoble

at 11 am amphi 23.01 campus Triolet – Université de Montpellier

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The famous city of Nicaea (where the first Christian Council was held) was established on the shore of Lake Iznik (Turkey), 5 km north of the middle strand of the North Anatolian Fault (MNAF). In 2014, a basilica was discovered in Lake Iznik; it was destroyed and submerged following an unknown catastrophic event. During this conference, we will follow the scientific investigations of an international team of 15 researchers from different disciplines (archaeology, tectonics, sedimentology, geophysics) in order to understand the seismic behaviour of the MNAF and see how it relates to the history of this basilica.

The MNAF is the slowest branch of the NAF, with a slip rate of < 5 mm/year. To reveal the seismic activity of this slow fault, we have developed new methods for investigating the timing and intensity of earthquakes, based on the stratigraphy of archaeological buildings, the dating of repairs and their modelling. The timing of seismicity was acquired independently by bathymetric, seismic and limnological studies of Lake Iznik and by geomorphological and palaeosimological studies of the fault segments on land.

As a result of these studies, two new fault segments were discovered in Lake Iznik, linked to the MNAF. The study of long sediment cores has made it possible to establish a chronicle of regional and local earthquakes over more than 6,000 years, with a recurrence of 1,000 years on the Iznik fault. The last earthquake to rupture the Iznik fault was in 1065 AD, which led to the destruction of the basilica. We have identified a seismic gap on the Iznik fault since 1065, which represents a major risk for the city of Iznik and the surrounding region.

Julia de SIGOYER is Professor in geodynamic at ISTerre, Université Grenoble Alpes. I have been studing the major continental fault zones from a scale of hundred million years to a year since 30 years. The first half of my career focused on long-term deformation of fossil subduction zones and intracontinental faults. Since 10 yrs, I work at short scale of time; developing archaeoseismological tools to get independent calendar of seismicity that is compared with the one from the study of lake and other palaeoseismological data to determine the segmentation, age and magnitude of past earthquakes.

 

 

Conférence GM & ED Gaïa :
Émissions et puits de CO2 dans le contexte des accords de Paris

par Pierre Friedlingstein

l’université d’Exeter

à 14h amphi 23.01 campus Triolet – Université de Montpellier

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La présentation résumera d’abord le cycle du carbone global actuel et l’importance de la perturbation anthropique en cours, décrivant les émissions de CO2 liées à l’utilisation de combustibles fossiles (pétrole, gas, charbon) et les émissions liées au changement d’utilisation des sols (ex. déforestation), ainsi que les puits continentaux et océaniques de carbone, leur dynamique spatio-temporelle et leur vulnérabilité au changement climatique en cours. Ensuite, la présentation abordera la quantification et incertitudes des émissions de carbone future (le « remaining carbon budget », RCB) compatibles avec les ambitions de l’accord de Paris de limiter le réchauffement global à 1.5°C ou 2°C, décrivant d’abord les concepts physiques liés au RCB avant d’aborder les aspects socio-économiques et technologiques tels que dans les scenarios futurs évalués par le GIEC, et pris en compte lors de la dernière Conférence des Parties des Nations Unies, la COP28 de Dubai.

 

Pierre Friedlingstein est Professor fellow de la Royal Society, Professeur à l’université d’Exeter, directeur de recherche CNRS au Laboratoire de Météorologie dynamique. 30 ans d’expérience dans les sciences du climat et cycle biogéochimiques. Membre du Joint Science Committee du World Climate Research Programme (WCRP), auteur pour le 4ème et 5ème rapport du GIEC.

 

 

Conférence GM & ED Gaïa : Observation de la phase pré-sismique du séisme de Gorkha, Mw 7.9 (Népal, 2015) par l’analyse de la micro-sismicité.

par Blandine GARDONIO

ENS, Laboratoire de Géologie de Lyon Terre – Planètes – Environnement

Vendredi 15 décembre 2023 à 11h amphi 23.01 et en ligne

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Ces dernières années, de nombreux séismes majeurs (magnitude supérieure à 7) ont donné lieu à des observations d’une phase pré-sismique. Bien que toujours faites à posteriori, ces études ont permis d’obtenir une meilleure compréhension des processus de nucléation des grands séismes. Lors de cette conférence, je vais présenter ces différentes observations et les questions qu’elles soulèvent. Je vais également montrer, avec l’exemple du séisme de Gorkha, magnitude 7.9, qui a eu lieu au Népal en 2015, comment on peut utiliser la micro-sismicité (magnitude < 3) pour détecter la phase pré-sismique. Nous avons utilisé 1800 séismes régionaux pour fouiller dans le signal sismique continu qui précède le choc principal afin de compléter les catalogues de sismicité. Nous avons mis en évidence une augmentation sur le long terme du taux de sismicité ainsi que plusieurs épisodes de crises sismiques. La crise la plus intense a lieu un mois avant le séisme et compte 38 séismes répétitifs localisés au nord ouest de la zone de rupture. Ces observations suggèrent que le séisme a été précédé par une phase pré-sismique potentiellement liée à la mise en place d’un glissement lent et à la présence de fluides près de la limite nord-ouest de la rupture.

 

Blandine GARDONIO est sismologue, chargée de recherche au CNRS, rattachée au Laboratoire de Géologie de Lyon depuis 2021. Elle a préparé sa thèse à l’ISTerre de Grenoble sur la sismicité de la subduction Japonaise puis elle a effectué un post-doctorat à l’ENS Paris pour travailler sur les analogues aux séismes profonds en laboratoire. Son deuxième post-doc s’est déroulé au CEA où elle a étudié la sismicité au Népal.

Conférence GM & ED Gaïa :
‘Bottom-up’ gas hydrate dynamics and seafloor fluid venting in collapsing deep-sea fans. Examples from the Amazon and Nile

par Daniel PRAEG

Géoazur, Nice.

à 14h amphi 23.01 campus Triolet – Université de Montpellier

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Gas hydrates frozen within deep-sea sediments form the largest reserve of carbon (mainly methane) on Earth. Their stability over time is sensitive to pressure and temperature changes, with strong implications for global methane cycling and continental slope stability. Submarine gas hydrate dynamics are usually seen in relation to ‘top-down’ changes in water column properties (sea level, temperatures), driven from above by climate. However, gas hydrate stability is also influenced from below by fluid migration within sedimentary successions. The Amazon and Nile deep-sea fans are rapidly-deposited depocentres that contain tectonic structures recording their gravitational collapse, as well as gas hydrate provinces associated with seafloor fluid vents. ‘Bottom-up’ changes in fluid expulsion and gas hydrate stability linked to tectonic movements may account for the giant landslides that characterize these and other deep-sea fans. Results are presented from French-Brazilian collaborations involving Géoazur, including initial results from the AMARYLLIS-AMAGAS campaign to the Amazon deep-sea fan in May-June 2023.

 

Daniel PRAEG is a marine geoscientist with interests in sedimentary and tectonic processes on continental margins in relation to geofluids. Originally a glacial geologist (meltwater drainage), his current focus is on the submarine cryosphere (gas hydrates). He is from Canada, and has lived and worked in the USA, Scotland (PhD 1997), Ireland, Italy, Brazil and France.