GEO 1111 Lecture Notes - Lecture 12: Orogeny, Shear Stress, Flattening

• School: University of Ottawa
• Department: Geology
• Course: GEO 1111
• Professor: David Schneider

Document Summary

Deformation: orogenesis applies force to rocks, causing deformation (bending, breaking, shortening, stretching, and shearing), change in shape via deformation is called strain. Deformation strain creates geologic structures: folds are bends in layered rock that form by shearing and or by slow plastic flow. Joints are fractures that have no offset: other geologic structures include faults (fractures that are offset) and foliation (a planar metamorphic fabric), deformation changes the character of the rocks and is often easy to see. Undeformed (unstrained) rocks display horizontal beds, spherical sand grains, no folds or faults. Deformed (strained) rocks show tilted beds, metamorphic alteration, folding, and faulting: deformation can include displacement, rotation, and distortion. Rotation is a change in spatial orientation. Distortion is a change in shape. (develop fault) Brittle deformation: there are two major deformation styles: brittle and ductile, the type of deformation depends on t and p conditions. In brittle deformation, which occurs in the shallower crust, rocks break by fracturing.