Geological Structures Flashcards
What is structural geology
Study of rock formation
What is another name for mountain building
orogenesis
What are the two terms used to describe different orientations of a flat surface
Strike and Dip
What does strike mean
the compass direction of the line of intersection on the dipping flat surface of INCLINED PLANES
What is dip
The angle between a horizontal plane and the inclined plane
What angle is the dip measured at
Measured perpendicular to direction of strike
What symbol is used to indicate the direction of the slip
a strait line parallel to the compass direction
What symbol is used to indicate the dip angle
a short tick mark with the angle next to it
what is the definition of stress
the force which causes strain
what are the types of stress
compression, extension, shear
what is shear stress
blocks of rocks SLIDING PAST each other
What are characteristics of compression
thickening material, found at convergent
what are characteristics of extension
thinning material, found at divergent boundaries
what are characteristics of shear stress
rocks neither thickened or thinned but some shape change, found at transform boundaries
what is the definition of strain
how a material reacts when stress is applied
what are key differences between stress and strain
stress is force applied and strain is the resulting deformation
what is displacement
change in location
what is rotation
change is orientation
what is distortion
change in shape
what are the two types of deformation types
brittle and ductile
what does brittle deformation show as
creates cracks
what does ductile deformation show as
creates folds
where does brittle deformation occur
closer to earths surface where temp is COOLER. COLD=BRITTLE
where does ductile deformation occur
deeper in the crust where temps are hotter and FLOW better
What is the other component of deformation types
strain rate. faster force means more likely breakage not flow
What are joints
fractures that have had no movement or shifting
What are characteristics of joints
- can be described by strike and dip
- typically in parallel strips
- result from tensional tectonic stress
- pathways for water and thus chemical weathering
What are faults
planar fractures where rock has been offset or shifted
What are characteristics of faults
- abundant and have variety of scales
- can be active or inactive
- vary by type of stress
what is a dipping fault
fault that is not straight up and down
What is the block above the fault called
hanging wall
what is the block below the fault called
footwall
What is a dip slip fault
when the fault plane is angled and the movement is parallel to the dip
What are the types of dip slip faults
normal, reverse, and thrust
What is the orientation of a normal fault
the hanging wall moves down relative to the foot wall
what causes normal faults
crustal extension (pulling apart)
What is the orientation of reverse and thrust faults
hanging wall moves up relative to the footwall
What causes reverse and thrust faults
crustal shortening (compressive stress)
What determines a fault as reverse or thrust
how steep/shallow the fault is dipping
What angle makes a fault reverse
steeper than 35
what angle makes a fault thrust
less than 35
What is a strike slip fault
fault motion parallel to strike of the fault (back and forth not up and down)
What determines a left or right lateral fault
the block opposite of where the observer is standing moves to either right or left side
What is oblique slip
combo of dip and strike slip motion
what is a hinge line
pint of max curvature along the fold
what is the hinge line/fold axsis
line connecting all the hinge points
what is a limb
less curved sides of a fold
what is an anticline
arch like or A shaped fold LIMBS DIP AWAY FROM HINGE
what is a syncline
U shaped fold LIMBS DIP TOWARD HINGE
what are flexural folds
layers that slip as stratified rocks are bent formed from compressional stress on either side
what are flow folds
non-uniform folds formed by ductile flow of hot soft rock
what rocks commonly have flow folds
igneous or metamorphic rocks
what is a plunging fold
a fold axis that is tilted or not level with ground surface
what is a non plunging fold
a horizontal fold axis level with the ground surface
what is dome
a fold that looks like an overturned bowl where layers dip away from center
