41 terms

Earth Science ch 7&8

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Orogeny
process of mountain-belt formation
Deformation
process during which rocks bend, break, or flow
Geologic structures
features produced by deformation, joints, faults, folds, and foliation
Displacement
change in location
rotation
change in orientation
distortion
change in shape
Strain
a measure of the amount of distortion during deformation
Plastic deformation
the process by which objects change shape without visibly breaking, creating folds in rocks
Temperature
Heat makes materials softer and more prone to plastic deformation.
Pressure
Greater pressures cause rocks to behave more like plastic and less prone to brittle deformation
Deformation rate
Sudden changes make materials more prone to brittle deformation, whereas slower change allows more plastic deformation
compression
takes places when an object is squeezed
tension
occurs when opposite ends of an object are pulled in an opposite direction
shear
develops when one surface of an object slides relative to the other surface.
pressure
occurs when an object feels stress on all sides
Dip-slip faults
Slip is vertical and takes place along the dip line of the fault. (Reverse and thrust &Normal)
Strike slip
Slip is horizontal and occurs along the strike line of the fault. (Left-lateral &Right-lateral)
Hanging wall
the wall above the fault line
Footwall
block below the fault line
Fault scarps
displacement along a fault that offset the ground surface
Slickensides
polished fault surfaces
Slip lineations
linear grooves on fault surfaces
fold
a curve in the shape of a rock layer
Anticline
arch-like fold where the limbs (sides of the fold) dip away from the hinge (line along which the fold has its greatest curvature)
Syncline
trough-like fold where the limbs dip toward the hinge
Monocline
fold shaped like a carpet draped over a stair step
Dome
shaped like an overturned bowl
Basin
shaped like an upturned bowl
Foliation
occurs where stress causes elongate or platy grains to align parallel to one another, such as in slaty cleavage textures
Convergent-boundary orogen
compression causing the crust to shorten and thicken
Collisional orogen
when relatively buoyant continental plates collide with one another
Accretion
occurs when smaller blocks are sutured to larger blocks. This process can widen a mountain belt
Rifting
caused by stretching, which creates normal faults. Movement along these faults causes blocks to drop down and tilt.
Isostasy
the balance between the forces that pull the lithosphere down and the forces that push it up
Cratons
continental lithosphere that has not been affected by mountain building events for at least the last 1 billion years
Shields
where Precambrian metamorphic and igneous rock are exposed at ground surface
Cratonic platforms
where a relatively thin layer of younger Phanerozoic sediments covers the Precambrian rocks
faults
fractures along which sliding or slip takes place
Focus (hypocenter)
location where the generation of seismic waves begins
Low-velocity zone
100-200 meters below surface
Seismic velocity discontinuities
abrupt stepping up of seismic velocities