Seminars

Isotopic dichotomy of meteorites // Dynamic instability of giant planets (title to be confirmed)
On zoom

Mineralogical and Geochemical approach to deciphering the collisionnal history of the L chondrites
Salle de réunion

Journée Cosmo-planéto
Amphithéâtre CRPG

Planetesimal rings as the cause of the Solar System’s planetary architecture
On Zoom

réunion info chercheurs
Salle de réunion

Discussion d’article
salle de réunion

New Radar Views of the Lunar South Pole Crater
On Zoom

L’hydrogène dans les chondres de chondrites carbonées : concentration, composition isotopique et spéciation
Amphithéâtre CRPG

Cosmic symplectite recorded irradiation by nearby massive stars in the solar system’s parent molecular cloud
Amphithéâtre du CRPG

A large proto-Mercury as the aubrite parent body
Amphithéatre CRPG / Zoom

From grain transport to landscape dynamic

Monitoring landslides in central Nepal using radar image correlation and comparison of Digital Terrain Models

Vitesses et causes du soulèvement du massif d’Oman

Résumé: David nous présentera en préambule différentes observations suggérant un soulèvement récent ou actif. L’ophiolite y est couverte par des sédiments marins tertiaires, ce qui suggère que son relief est récent. La disposition de terrasses alluviales le long des «wadis» suggère aussi un soulèvement récent. Des études sur des terrasses marines montrent un soulèvement de la côte depuis 20 000 à 700 000 ans, avec des taux de soulèvement surprenants et contradictoires (de 0.5 à plus de 6 mm/an!). Il serait intéressant de voir si l’étude des terrasses dans l’ophiolite peut aider à comprendre la cause et l’évolution de ce relief.

Pleistocene evolution of denudation rates of south-western Madagascar

Interferométrie SAR : Séries temporelles et application

Sediment generation and recycling at convergent plate boundaries (Indo-Burman-Andaman-Nicobar and Barbados Ridges)

The sprawl of the Peloponnese or how I learned to stop worrying and love gravity tectonics

Résumé: The Peloponnese (Southern Greece) belongs to the External Hellenides, an alpine orogeny that reached the late phase of its evolution during Miocene times. As it is the case for most of the alpine belts spread along the southern Eurasian margin, its deformation is now dominated by the gravitational collapse of its topography and the subsequent exhumation of deep metamorphic units. Southern Greece, however, is simultaneously located on the overriding plate of the Hellenic subduction, where the slab rollback already delaminated the Aegean part of the chain by a factor of two or more in the Neogene. The Peloponnese, still at a less advanced, more brittle stage of collapse, is therefore a remarkably suitable playground for studying the competition between volume and boundary forces in the early stages of orogeny dismantling.

Lithology and Tectonics: Building the inorganic carbon budget of a young  mountain range

Erica Erlanger, Aaron Bufe, Guillaume Paris, Ilenia D’Angeli, Luca Pisani, Preston Kemeny, Jessica Stammeier, Negar Haghipour, Niels Hovius

Résumé: Mountain building has classically been linked with CO₂ drawdown from chemical weathering of silicate minerals in the critical zone, although recent views on mountain building recognize the importance of rock-derived CO₂ emissions from the weathering of petrogenic organic carbon and inorganic carbonate. However, the focus on near-surface weathering reactions within the orogenic carbon factory does not consider the emission of metamorphic CO₂ from subduction processes in the deep crust and mantle. Such deep carbon sources could dwarf the surficial drawdown and release of carbon, in particular in actively extending mountain ranges that subduct large volumes of carbonate rock. Thus, accounting for weathering processes at depth and in the critical zone in parallel is crucial to fully assess how mountain-range uplift impacts the carbon cycle. Here, we quantify the exchange of CO₂ between rock and the atmosphere from subduction-related processes and from critical zone weathering reactions in two major river systems in the central Apennine Mountains of Italy. The catchments straddle a geodynamic gradient across the subduction zone that is expressed as changes in surface heat flow and crustal thickness, whereas climatic boundary conditions are relatively constant.  At the regional scale, we find that metamorphic CO₂ sources outpace critical zone inorganic carbon sources and sinks by 2 orders of magnitude above a window in the subducting slab that is characterized by high heat flow and low crustal thickness, and could have driven efficient degassing over the last 2 Ma. In contrast, surficial weathering processes dominate the carbon budget where crustal thickness is greater and heat flow is lower. Importantly, the difference in metamorphic degassing fluxes across the geodynamic gradient is multiple orders of magnitude larger than the difference in critical zone weathering fluxes. Thus, modulations of metamorphic decarbonation reactions are the most efficient process by which tectonics can regulate the inorganic carbon cycle in the Apennines. Both near-surface and deep sources of CO₂ must be considered when constructing the carbon budget of orogenic systems that include the subduction of carbonate rock.

Reconstructing topography of the Equatorial Variscan belt

Résumé: The first stable isotope paleoaltimetry estimates have been recently acquired for the internal zones of the eroded Variscan Belt of Western Europe (Limousin region) based on the hydrogen isotope ratios (δD) of muscovite from syntectonic leucogranites that have been emplaced at ~315 Ma. The results point to locally sourced waters that originated at high elevations (3.4 ± 0.7 km) in an area with strong relief, most likely forming a Late Carboniferous topographic high within the Variscan hinterland. Although we are limited in extrapolating isotope elevation relationships into the distant past, our results indicate that this Variscan area was high enough to block air masses from the SE and induces an orographic rainshadow to the North.A minimum mean elevation of ~ 3.4 km is reinforced using a new empirical relationship between elevation and the stable isotope composition of precipitation and surface waters (-1.5‰/km for δ¹⁸O & -14‰/km for δD) established across the Western Southern Ecuadorian Andes, which, like the Variscan belt was during the Carboniferous, is located at (or near) the Equator.

Explorer l’évolution géomorphologique d’un bassin versant de montagne par la modélisation du 10Be in situ dans des profils d’altération à haute résolution, des sols et des sédiments de rivière (Observatoire du Strengbach, OHGE, Vosges, France)

Résumé: Une riche base de donnée combinant des analyses de 10Be in situ dans des profils d’altération à haute résolution spatial, des échantillons de sol et des sédiments de rivière a été interprétée pour explorer l’évolution géomorphologique d’un bassin versant de montagne (Observatoire du Strengbach, OHGE, Vosges, France). La variabilité spatiale des taux de dénudation indique que la géomorphologie du bassin évolue d’une manière dynamique : une érosion fluviale régressive incise la partie aval du bassin versant alors que les zones sommitales s’érodent moins rapidement. L’étude permet également de détecter la présence de régolithe mobile le long des pentes, et montre comment la structure actuelle de la zone critique est impactée par ce processus important. La diversité des approches permet également d’estimer l’impact d’une hypothèse fréquemment réalisée dans la communauté des isotopes cosmogéniques : l’hypothèse d’état stationnaire des concentrations de 10Be. Notre étude montre que les états stationnaires pour les concentrations de 10Be, pour le bilan de masse du régolithe et pour la géomorphologie d’un bassin versant ne sont pas toujours atteint dans la même fenêtre temporelle. Dans le cas du Strengbach, un état stationnaire pour l’épaisseur des sols est atteint avant celui des concentrations de 10Be in situ, démontrant que cette hypothèse d’état stationnaire des concentrations de 10Be in situ doit être prudemment utilisée dans des contextes de montagne.