Tectonics & Mountain building
Associated with plate tectonics
Most common at Plate boundaries
Two (or more) plates interact along huge linear zones of faulting
Tectonic activity is common here
The amount of energy involved here is immense
The movement of large areas of the crust vertically & horizontally
Immense stresses at an extremely slow rate (2nd Law of GeoFantasy)
Different sections of the crust are moving at different velocities
Therefore they interact at their edges - plate margins
All this up and down involves distorting the crust
Several things can happen
Break - fractures & joints
Break & slip - faults
Fold
What happens depends on
Rock type
Temperature
Type and magnitude of the force (stress)
When cold rock moves, it can break
Must be relatively cold and brittle
Called fractures, or joints
Breakage without movement
Faults: A fracture where the sides have moved relative to each other
Usually a planar surface
Hangingwall vs. footwall
Several types of faults, based on the relative sense of motion
Normal faults - hanging wall down
Usually the result of tension and crustal lengthening
Horst & Graben (see fig. 8-13; pg. 171)
Actually Valley Building, not Mountain Building
Reverse Fault - hanging wall up
Common at convergent boundaries
Results in shortening of the crust
Strike-slip faults
Offset spreading centers
Folding as a result of directed stress at depth
Below the Brittle-Ductile Transition Zone
Generally associated with convergence & shortening of crust
Push a rug against the wall
Anticline/syncline
Come in sets - rarely alone