Séminaire de Suzon Jammes, Texas State University

Deformation of bimineralic materials and their effect on extensional processes at lithospheric scale

Séminaire de Suzon Jammes, 2019

Résumé

Geological observations show that minerals harder than their surrounding matrix tend to remain almost undeformed or to undergo localized fracturing while the rest of the material shows evidence of viscous deformation. In these polymeralic materials the deformation localization is therefore strongly dependent on the mechanical behavior of the dierent phases, the proportion, and the strength contrast between them. If these parameters vary at the scale of a rock sample, they also vary at lithospheric scale when units with dierent lithologies are juxtaposed leading to the strongly heterogeneous crust and mantle. In the lithosphere, moreover, the dependence with depth of the pressure-temperature imposes that the strength ratio between the dierent phases is also dependent on the depth and geotherm.

These observations suggest that a polymineralic assemblage has a strong inuence on deformation processes and localization of the deformation from the microscopic to the lithospheric scale. To investigate the role of bimineralic composition on deformation processes at dierent scales, we perform numerical experiments using an explicit bimineralic composition by
distributing two mineral phases in the materials. Two set of experiments are presented and discussed in comparison with geological observations :

1) Meter scale numerical models with a quartzofeldspathic assemblage using shearing boundary conditions leading to a fracture-like localization
2) Lithospheric scale models in extensional setting using a bimineralic composition in the crust and the mantle to take into account the compositional heterogeneities.

To investigate the effect of crustal heterogeneities inherited from previous tectonic phases on magma-poor rifting processes, mineral phases are distributed in a way that is compatible with the orientation and distribution of kilometric-scale heterogeneities observed in seismic reection data. The results will be compared to the Northeastern Canadian margin and insights on the variability of architecture of the margin is discussed.