Deformation

Deformation - all changes in the original form and/or size of a rock body

Stress - force/area

Strain - change in length/original length

Strain rate - determines whether material behaves in a brittle (breaks) or ductile (plastic faction. Equal to strain/time

3 types of stress orientations - compression, tension, or shear

Compressive forces - squeeze and shorten rocks

Tensional Forces - stretch and pull rocks apart

Shearing forces - shear two parts of a rock formation in opposite directions

Types of deformation - elastic, plastic, brittle

Elastic - temporary deformation in response to applied stress, rock returns to original shape when stress is removed

Plastic  - permanent deformation in response to an applied stress, rocks does not return to original shape

Brittle deformation - rock stressed to point of failure

folding: type of ductile deformation; two types: anticline and syncline

Anticline - ductile; upfolded, or arched, rock layers (A shaped); oldest rock in center

Syncline - ductile; downfolded rock layers (U shaped) youngest rock in center

Symmetrical folds - ductile; have limbs that dip symmetrically from the axial plane

Asymmetrical folds - ductile; have one limb that dips more steeply than the other

Overturned folds - ductile; have limbs that dip in the same, but one limb has been tilted beyond the vertical

Plunging  fold - ductile; has an axis at an angle to the horizontal

Dome - ductile; oldest rocks exposed on the surface and youngest formation at edge

Basin - ductile; youngest rocks in core

fault  - zone of localized, brittle deformation

Dip Slip fault - movement along the inclination (dip) of a fault plane; includes normal, reverse and thrust

Strike slip fault - dominant displacement is horizontal and parallel to the trend or strike

Three types of faults - reverse faulting, normal faulting, strike slip faulting

Reverse faulting - caused by compression; hanging wall block moves up; dips greater than 45

Normal faulting - caused by tension; hanging wall moves down

Strike slip faulting - caused by shearing

Pseudotachylyte - veins of glassy rocks formed from frictional melting during earthquakes, landslides, impact events, and other high friction events.

Slickenlines/fibers - mineral fibers precipitated in open fault zones and/or polished surface and lines gauged by small protrusions

Geologic cross sections - diagrams showing the features that would be visible if vertical slices were made through part of the crust

Strike - the orientation of a horizontal line within a plane

Dip - the angle a layer of rock is tilted with respect to horizontal

Tensional tectonics - extension of continental crust produces normal faults with high dip angles in the upper crust that flatten with depth, forming curved fault surfaces