Crustal Deformation & Mountain Building

• Deformation is a general term that refers to all changes in the original form and/or size of a rock body.
• Most crustal deformation occurs along plate margins.

• Temperature
• Confining Pressure
• Rock Type
• Time

Force per unit area or the force applied to rocks

• Compression
• Tension
• Shear

Action of oppositely directed forces acting towards each other at the same time

Action of coinciding and oppositely directed forces acting away from each other.

Action of coinciding and oppositely directed forces acting parallel to each other across a surface

• Rocks bent into a series of waves
• Most folds result from compressional forces that shorten and thicken the crust

• Anticline
• Syncline

Can be symmetrical, asymmetrical, overturned, or plunging.

Upfolded or arched rock layers; a sequence of folded rocks with the oldest rocks on the inside of the fold.

Downfolded rock layers; a sequence of folded rocks with the youngest rocks on the inside of the fold

Limbs are mirror images

Limbs are not mirror images

One limb is tilted beyond the vertical

Where folds die out or tilt

• Dome
• Circular
• Oldest
• Basin
• Downwarped
• Youngest

Circular or slightly elongated

circular displacement of rocks

Oldest rocks in core

Circular or slightly elongated

downwarped displacement of rocks

Youngest rocks in core

• Strike
• Dip

compass direction of an inclined rock layer as it intersects with a horizontal surface

Acute angle between the rock layer and the horizontal surface, measured perpendicular to the strike of the inclined rock layer (amount of tilting of the rock layer)