Room: 407 Tel: Patrice Rey

Lecture 2: Plate boundaries, Stress, and Lithospheric deformation Aims: Review the consequences of lithospheric deformation Plate boundaries are the privileged locus for deformation. We will see that 3 sorts of plate boundaries can be defined each having a particular stress regime. We will see that under the action of stresses rocks deform in different manners: Elastic (like rubber), brittle (like glass), and plastic (like putty).

Topography and seismicity are the two most obvious consequences of lithospheric deformation......Zone of Seismicity => High topography

Crustal thickness gradient => High topography and seismicity

Isostasy and surface topography

Area of large topography occur at convergent plate boundaries

Regions of large topography gradient Convergent plate boundaries

Regions of large topography gradient Convergent plate boundaries

Regions of large topography gradient Divergent plate boundaries

Transform fault, and strike slip fault boundaries

Area of large topography are not restricted to thickened crust The Basin and Range Province (West US)

Where plates interact, rocks are subjected to stress. Stress is the force per unit area. Compression occurs at convergent plate boundaries Stress and deformation at plate boundaries Deformation is a response to stress. There are three main stress regimes:

Tension occurs at divergent plate boundaries Shearing stress occur at transform boundaries Stress and deformation at plate boundaries Type of structures that accommodates deformation depends on the stress and therefore on the tectonic regime.

When subjected to stresses, rocks strain in different ways: Types of deformation: Elastic, Brittle, and Plastic deformation Some factors affecting deformation: Lithostatic pressure, temperature, and time.

Tectonic regimes and deformation

Lecture 2 at a glance Three types of plate boundaries: Convergent, divergent, transform, each characterized by a particular stress regime. Three types of stress regimes: Compression, tension, shear Three types of deformation: Elastic, brittle, plastic. Convergent plate boundaries: Compression Reverse faults, and thrusts Folds (fold and thrust belt) Divergent plate boundaries: Tension Normal faults, (horst and graben) Volcanism Transform plate boundaries: Shear stress Strike slip faults