(class notes) 14 Rock Deformation and Folding

Deformation

Changes of location, orientation, or shape of a rock

displacement

rocks changed in location

rotation

rocks rotated, change in orientation

distortion

rock’s shape is changed

stress

force per unit area,

usually caused by plate tectonics, can also can be caused by weight of overlying rocks

4 way rocks can react to stress

1. fracturing

2. faulting

3. folding (a wrinkle of a rock layer)

4. flowing

confining pressure

Stress applied uniformly in all directions

compression stress

convergent plate boundary, squishes a rock

tension stress

divergent plate boundary, rips rock apart

shear stress

transform plate boundary, results in slippage

stain

response to stress; stretching, shortening, and shearing

elastic deformation

reversible

plastic (ductile) deformation

bends, not reversible

Heat, high confining pressure, low strain rate, rock types and composition, water (being wet)

Makes rock more likely to have ductile deformation instead of fracturing

hinge line

where the rock bends

axial plane

imaginary plane at hinge line

anticline

top of arch, upfolded

Syncline

bottom of dip, downfolded

Isoclinal Folds

limbs are symmetrical and parallel, more than one fold

Asymmetrical Fold

limbs in fold are not the same

Overturned fold

axial plane is tilted

recumbent fold

extreme overturned, axial plane is horizontal

Chevron Folds

Zig-Zag, straight limbs and sharp hinge

Plunging fold

axial line is plunging into the ground, tilted into the ground

dome

oldest in the center

basin

youngest in the center

monocline fold

just goes up, only one limb, like a ramp