GEOL 101 Exam Review 3

Craton

Very old, strong, and stable continental crust, consisting of the oldest rocks on Earth.

Shield

Precambrian igneous and metamorphic rocks exposed at the surface, forming the core of continents.

Orogenesis

The process of mountain formation due to plate interactions, involving convergence and divergence.

Convergence

Mountains form where new crust has been added onto the craton. → ←

Subduction

Process where one tectonic plate moves under another, leading to the formation of volcanic arcs and fold-thrust belts.

Accretion of exotic terranes

Island fragments of continental crust with distinct geological histories merging at convergent margins.

Divergence

Mountains form where crust has been ripped apart from it. ← →

Continental to continental collisions

Convergence of continents leading to high-grade metamorphic rocks and fold-thrust belts.

Rotation

A change in spatial orientation by tilting.

Displacement

A change in location by fracturing. Examples include jointing and faulting.

Distortion

A change in shape by folding.

Brittle

Shallow in crust

Ductile

Deep in crust

Fault

Planar breaks in the crust showing displacement, classified by relative motion and geometry (e.g., normal, reverse, thrust, strike-slip).

Anticline fold

Arch-shaped fold where limbs dip out and away from the hinge.

Syncline fold

Trough-shaped fold where limbs dip inward and toward the hinge.

Dome

Fold resembling an overturned bowl, exposing older rock in the center.

Basin

Fold shaped like an upright bowl, exposing younger rocks in the center.

Stress

Force applied across a unit area, leading to deformation.

Strain

Change in shape or volume in response to stress, with compression, tension, and shear as types of strain.

Mohorovicic discontinuity (Moho)

A distinct boundary between the crust and the mantle where seismic waves are refracted.

Low-velocity zone (LVZ)

Occurs beneath the crust (from 100-200 km) - the asthenosphere.

P-wave shadow zone

Area where P-waves do not arrive at seismometers between 103° and 143° from the epicenter due to refraction.

S-wave shadow zone

Area where S-waves do not arrive at seismometers between 103° and 180° due to inability to travel through liquids.

Paleomagnetism

Studies how Earth's magnetic field is recorded in rocks, aiding in understanding past tectonic movements.

Ridge push

Force driven by gravitational energy associated with the topographic elevation of the mid-ocean ridge.

Slab pull

Force developed due to the denser old oceanic lithosphere sinking into the underlying asthenosphere.

Compression

Deformation shortens and thickens the crust.

Tension

Deformation lengthens and things the crust.

Shear

Deformation neither thickens or thins the crust.

Dip-slip faults

Characterized by blocks that move parallel to the dip of the fault (vertical).

Normal fault

Hanging wall moves down relative to footwall.

Reverse fault

Hanging wall moves up relative to the footwall - high angle > 30°.

Thrust fault

A type of reverse fault but with a low angle dip, < 30°.

Strike-slip fault

When blocks move parallel to the fault plane strike. Tend to be vertical.

Right lateral strike-slip fault

Fault block appears to move sideways and to the right past the observer’s block.

Left lateral strike-slip fault

Fault block appears to move sideways and to the left past the observer’s block.

Folds

Occur where rock has been deformed deep below the surface from tectonic compression (continental to continental convergent boundaries).