Deformed rocks Flashcards
Mountains/Mountain building
Mountain Building
Orogenesis
Uplift
Deformation
Metamorphism
Mountain building events are called “orogenies”
Evidence of tectonism
Mountain belts are (geologically) temporary and ever-changing
Constructive and destructive processes
ask yourself what tectonic process might have made it. Is it active now or was it a long time ago?
deformation
rocks deform in response to directional stress
Ductile deformation: (more bendy)
High temperatures
Long periods of time
Brittle deformation (spaghetti noodles we broke)
Low temperatures
Short periods of time
brittle deformation
Brittle
Fast
Cold
Stress exceeds the breaking point
Irreversible break
ductile deformation
Ductile
Slow
Warm
Stress does NOT exceed the breaking point
Irreversible change in size and/or shape (when pressures are removed it doesn’t snap back)
Volume and density may change
undeformed/deformed rocks
Undeformed rocks have horizontal beds, spherical sand grains, no folds and faults, have to have them to have deformed rocks
Deformed rocks show tilted beds, metamorphic alteration, folding and faulting
displacement
rotation
distortion
dis: slide down
rotate
distortion: stretch, bend, etc.
strain types
Stretching(divergent)
Elongation
Shortening(convergent)
Contraction
Shear(transform)
Opposing forces
stress
Strain is the result of deformation
Deformation is caused by force acting on a rock and that force is called stress
Type of stress
Compression
Tension
Shear
Pressure
compression
convergent
Material is squeezed
Shortens and thickens
Drives collision and orogenesis
causes most of our mtn building events
tension
divergent
Material is pulled apart
Stretches and thins
Drives crustal rifting
causes our mtn range building
shear
transform
Surfaces slide past each other
Neither thickens nor thins
pressure
Equal stress on all sides
like a diver under water
Measuring and communicating the geometry of the geologic structure:
strike and dip
Orientation of imaginary planes
(No, not Wonder Woman’s)
Dip
Angle of inclination downward (steepness of the inclined plane)
(if you spit on it which way would the spit roll)
Strike
Compass direction (such as 95 degrees from North) of a horizontal line (pretend to fill with water which creates a horizontal line, direction is where the line aligns with the inclined plane)
Where the inclined plane intersects an imaginary horizontal plane
helps us understand what caused the deformation
structural features: joints
Brittle deformation
No displacement or shear
Usually formed as overburden is removed
Also formed by cooling of igneous rocks
Significance?
Fluid flow, groundwater, oil, ore, weathering into beautiful Bryce Canyon…
structural features: veins
Joints allow groundwater flow
Mineral-rich groundwater can deposit veins of minerals in the joints
Example: limestone from Rock Canyon
cracks happened, and those are filled with minerals (ex: dark rocks with white veins)
structural features: faults
Brittle
Fractures where displacement has occurred
Two blocks are defined
One on either side of the fault
Strike-slip: Right lateral vs Left lateral
Imagine yourself standing looking over the fault to the other side. Which way did the other side move relative to you?
fault practice
find hanging wall:
if it moves down: normal
moves up: reverse
stustural features: folds
Rock layers are warped due to ductile deformation
Horizontal compression (orogenies)
Can have multiple episodes of folding
Classification
Strike of the hinge line
Dip of the limbs
Anticlines, Synclines, Monoclines, etc
anticline
Warp upward
Dips away from middle
Strike is horizontal to ground surface
Makes a frown or an “A”
Oldest layers exposed in the center
syncline
Warp downward
Dip toward middle
Strike is horizontal to the ground surface
Makes a smile or a “U”
Youngest layers exposed in the center (bottom is oldest layers)
monoclines
Dip only in one direction
Strike is horizontal to ground surface (doesn’t dip below ground)
plunging fold
Strike (or fold axis) is dipping or “plunging”
Can be anticlines or synclines or even monoclines
“Plunging anticline” etc.
Sheep Mountain, WY
Virgin Anticline, Hurricane, UT
quail creek resevoire** cool to visit
domes and basins
Generally occur in continental interiors
Broadly warped regions
Roughly circular patterns
Domes
Oldest strata in middle (upside down bowl, water runs down to edges away from middle)
Basins
Youngest strata in middle
all comes down in the middle, (water gathers in the middle) multiple pressures in areas farther away from specific pressure points
the richat structure (woah beautiful)
Sahara Desert of Mauritania
At first believed to be an impact crater
Now has been mapped as a structural dome
know how to tell which layers are older
Mountains– Continental-Continental Convergence
most pervasive or largest mtns in the world
Mountains—Divergence
rift margins rise to form mountains
rifts and horsts
mt timp
