Download Mountain Building Chapter 10 Learning Standard: I will analyze the

Mountain Building
Chapter 10
Learning Standard: I will analyze the theories associated with geologic events that change the earth’s
physical environment.
Learning Target: I will compare different types of mt-building processes and the resulting structures of
each process.
Deformation
__________________ is a general term that refers to all changes in the original form and/or size of a
rock body
Most crustal deformation occurs along plate margins
Factors that influence the strength of a rock
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_______________ and confining _________________
_________________ ______________
_____________
•Types of deformation:
•1. _________________ – change that can be recoverable, like a rubber band.
Stress is gradually applied
but when released, earthquakes are generated (elastic rebound)
•2. ________________ – rock fractures,
•temps and pressure are low
•Happens near the Earth’s surface
•3. _______________ – rock changes in size and shape without fracturing
•Temps and pressure are high
•Happens deep under the Earth’s surface
•Brittle and Ductile deal with mountain building processes and occur due to temperatures and confining
pressures.
Folds
Rocks bent into a series of waves
Most folds result from compressional forces which shorten and thicken the crust
Types of folds
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_________________ – upfolded, or arched, rock layers
_________________ – downfolded rock layers
Anticlines and synclines can be
• ________________________ - limbs are mirror images
• ________________________ - limbs are not mirror images
• ________________________ - one limb is tilted beyond the vertical
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Where folds die out they are said to be plunging
Other types of folds
• ____________________
• Circular, or slightly elongated
• Upwarped displacement of rocks
• Oldest rocks in core
• Younger rocks on the outer ends
• ____________________
• Circular, or slightly elongated
• Downwarped displacement of rocks
• Youngest rocks in core
• Oldest rocks on the outer ends
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Illinois is considered a basin.
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Pennsylvanian age rocks (286 million years)
• South-central part of the state
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Mississippian age rocks (320 million years)
Devonian age rocks (362 million years)
Ordovician age rocks (441 million years)
• Northern part of the state
Ozark Dome
– Encompasses most of Missouri
– Oldest rocks start in Southeastern Missouri with the St. Francois Mts.
– Precambrian rocks in the center (544 million years and older)
– Cambrian (505 million years)
– Ordovician (441 million years)
– A little Silurian/Devonian (362-418 million years)
– Mississippian (320 million years)
– A lot of Pennsylvanian (286 million years)
Faults
Faults are fractures (breaks) in rocks along which appreciable displacement has taken place
Types of faults
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___________-______________ fault
• Movement along the inclination (dip) of fault plane
• Parts of a dip-slip fault
• ________________ wall – the rock above the fault surface
• ________________ – the rock below the fault surface
Types of dip-slip faults (Normal and Reverse
• ____________________ fault
• Hanging wall block moves down
• Associated with fault-block mountains
• Grand Tetons of Wyoming
• Prevalent at spreading centers
• Caused by tensional forces
• Create horsts and grabens
• Series of uplifted blocks and downward valleys
Second type of dip-slip fault
________________ and thrust faults
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Hanging wall block moves up
Caused by strong compressional stresses
Reverse fault - dips greater than 45º
Thrust fault - dips less than 45º
______________-__________ faults
• Dominant displacement is horizontal and parallel to the trend, or strike
• Transform fault
• Large strike-slip fault that cuts through the lithosphere
• Often associated with plate boundaries
Other Fractures in the crust
_____________
• Fractures along which no appreciable displacement has occurred
• Most are formed when rocks in the outer-most crust are deformed
Mountain belts
____________________ refers to processes that collectively produce a mountain belt
Mountain building at ________________ boundaries
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Most mountain building occurs at convergent plate boundaries
Aleutian-type mountain building
• Where two oceanic plates converge and one is subducted beneath the other
_______________________refers to processes that collectively produce a mountain belt
These events are called ________________________
______________________ at convergent boundaries
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Types of Mountains:
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1. _______________ Mountains
2. _______________ Mountains
3. _______________ Mountains
4. _______________Mountains
Other Structures
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Most mountain building occurs at convergent plate boundaries
1. _________________
2. _________________ Plateaus
________________________ Mountains
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Mountain ranges made from igneous/volcanic activity
Usually associated with subduction zones
Examples:
• Cascades
• Western Andes
• Japan
• Philippines
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____________________ Mountains
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Occur when rock strata is twisted and folded
Regional, high-grade metamorphism
Associated with some continental-continental convergence
Compressional stresses with reverse and thrust faulting
Anticlines and synclines are present
• Examples: Himalayas, Appalachians, N. Rockies
__________________________________
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Third mechanism of mountain building
Small crustal fragments collide with and accrete to continental margins
Accreted crustal blocks are called terranes
Occurred along the Pacific Coast
_____________________________ Mountains
– Tensional stresses pulling crust apart
– Associated with normal faulting
– Formed by the displacement of rock along a single fault
– Horsts and grabens
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Examples: Grand Tetons (WY), Sierra Nevada (CA), Basin and Range (UT, NM, AZ, CA)
_________________________ Mountains
– Associated with doming episodes
– Associated with reverse faulting and compressional stresses
– Faults on two sides of the mt. range
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Examples: Southern/Colorado Rockies, Black Hills, Adirondacks
Rocky Mountains
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Southern Rockies
– Colorado Rockies, Sangre de Cristo Range in New Mexico, and Big Horns in Wyoming
• Upwarped Mountains
– Different from the Northern Rockies
• N. Rockies are Folded
– Formed during the Laramide Orogeny (60 million years ago)
• Was not associated with mt. building at plate margins
• Orogenesis that occurred within a plate
• Due to nearly horizontal subduction, not vertical
• One of the last Mt. building episodes of western N. America (Cordilleran)
How these Rockies Possibly Formed
A nearly horizontal subducting plate (Farallon plate) moved eastward under western N. America
This type of subduction caused compressional stresses and major thrust faults in western N. America
The plate broke off from the lithosphere and sank into the asthenosphere
As the plate sank, it melted causing hot rock to replace it
This hot rock provided the buoyant force necessary to raise the southern Rockies, the Colorado Plateau,
and The Basin and Range province
This upwelling lifted ancient basement/igneous rocks and provided tensional forces to form high angle
normal faults
Thus leading to a mountainous topography surrounded by sediment filled basins
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Other Structures
– ________________: uplift of flat land with little deformation.
– Generally created behind mt ranges
– Features of plateaus:
• Mesas and Buttes
• Example: Colorado Plateau
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____________________ Plateau
– A highly eroded plateau
– Erosion by streams and rivers cutting through the uplifted area
– Examples
• Ozark Plateau
• Cumberland Plateau
Ozark nonMountains
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Ozark Dissected Plateau
A highland dome
– Encompasses most of Missouri
– Oldest rocks start in Southeastern Missouri with the St. Francois Mts.
• Igneous rocks
• (544 million years and older)
– The surrounding rocks are primarily limestone and dolostone
• Range from 505 million years to 286 million years
• Deposited by a vast sea in the Paleozoic era (540 m.y to 250 m.y)
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Separated into three sections
– Salem Plateau
• Central to SE Missouri
– Springfield Plateau
• SW Missouri
– Boston Mountains
• Northern Arkansas
Mountain belts
Buoyancy and the principle of _____________________________
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Evidence for crustal uplift includes wave-cut platforms high above sea level
Reasons for crustal uplift
• Not so easy to determine
• Isostasy
• Concept of a floating crust in gravitational balance
• When weight is removed from the crust, crustal uplifting occurs
• Process is called ____________________________