Crustal Deformation Flashcards
What are stress and strain?
Stress is the directed pressure acting on a rock, and strain is the resulting change in its shape and/or size.
What are the two main types of deformation?
Brittle deformation (resulting in faults and joints) and plastic (ductile) deformation (resulting in folds).
What’s the difference between elastic and plastic deformation?
Elastic deformation is reversible once stress is removed, while plastic deformation is permanent.
Which factors control how rocks deform?
Temperature, confining pressure, rock type, and time.
How do geologists map rock structures?
By measuring strike (the trend of a rock layer’s intersection with a horizontal plane) and dip (the angle of inclination from horizontal), using tools like aerial photos, satellite imagery, and GPS.
What is a fault?
A fracture in rock along which there has been significant displacement, often causing earthquakes.
What characterizes a normal fault?
It forms under tensional stress where the hanging wall moves down relative to the footwall, accommodating crustal extension.
How do reverse and thrust faults differ from normal faults?
They form under compression; reverse faults have dips greater than 45° while thrust faults have dips less than 45° (often at convergent boundaries).
What are strike-slip faults and their subtypes?
They exhibit mostly horizontal movement parallel to the fault’s strike, including right-lateral and left-lateral faults; transform faults are large-scale examples.
What are slickensides?
Polished, striated fault surfaces created as rock blocks slide past one another.
How are earthquakes related to crustal deformation?
They occur from sudden displacement along faults due to brittle failure, with the most destructive events often along strike-slip and low-angle thrust faults.
What causes folds in rocks?
Plastic deformation under compressional stress in deeper, warmer regions of the crust causes layers to bend and form folds.
What are the main types of folds?
Anticlines (upfolded arches), synclines (downfolded troughs), recumbent (overturned) folds, and plunging folds; monoclines are also mentioned.
What are the key parts of a fold?
Limbs (the sides), the axis (line of maximum curvature), and the axial plane (the surface that divides the fold symmetrically).
How do domes and basins form and differ?
Domes are upwarped structures with the oldest rocks in the center, while basins are downwarped with the youngest rocks in the center; both often show circular patterns.
