Séminaire ISTerre

The emergence of proto-plate boundaries from lithospheric drips with grain-damage

mercredi 7 octobre 2026 - 11h00
Pr David Bercovici - Yale University
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The emergence of plate tectonics in the early Earth may have started with convective downwellings or drips, which induced localized damaged zones in the lithosphere that eventually accumulated and organized into a network of weak plate boundaries. To address the question of how early downwellings might have localized into damage zones, we explore a simple theory for dripping lithosphere with two-phase grain damage. This model involves only a gravitationally unstable lithosphere overlying a relatively inviscid asthenosphere, and underlying a mobile floating layer of crust that can pile up over downwellings or thin over upwellings. The lithospheric layer has a composite rheology with dislocation creep and grain-size sensitive diffusion creep; grain-size evolves according to the theory of two-phase grain-damage with Zener pinning. Linear stability analysis of the model displays mode selection at finite wavelengths, and the peak growth rate and least-stable wavelength are strong functions of crustal mobility. Nonlinear solutions to the full model predict that, for a range of simple or random initial conditions, self-organizing and highly localized, lineated upwellings, downwellings and weak zones emerge by connecting proximal drips (or upwellings) to each other. Results suggest that essential localized weak zones leading to lineated plate tectonic boundaries can spontaneously arise from post-Hadean lithospheric drips.

Equipe organisatrice : Géodynamo

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

Statistical physics of creep rupture of heterogeneous materials

jeudi 15 octobre 2026 - 11h00

JUAN CARLOS VERANO ESPITIA  - ISTerre - Aalto University (Finlande)

Equipe organisatrice : Mécanique des failles

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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The Seismic Response of Faults to Weak Perturbations: A New Probe Into Earthquake Physics and Fault State

vendredi 6 novembre 2026 - 11h00

Eric Beaucé - ISTerre

Equipe organisatrice : Cycle sismique et déformations transitoires

Salle Dolomieu, Maison des Géosciences, 38400 Saint Martin d'Hères

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TBA

vendredi 13 novembre 2026 - 14h00

Farzaneh Mohammadi - ENS Paris

Equipe organisatrice : Cycle sismique et déformations transitoires

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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Effects of iron and volatile elements on the local structure and density of deep silicate melts

lundi 23 novembre 2026 - 14h00

Lucie Canet (Thesis defense) - ESRF

Equipe organisatrice : Géodynamo

Amphithéâtre Killian, Maison des Géosciences, 38400 Saint Martin d'Hères

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