Large circular downwarped structures are called ________.
answer
basins
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A circular to elliptical structure developed by upward arching of the central strata is a(n) ________.
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dome
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Part A - The style of deformation
What type of deformation is shown in the Gigapan image?
answer
ductile
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Interpretation of the folds of this outcrop can provide the geological history of this region. They tell a story about what happened years ago. What is the order of events and the result of stress and deformation? Note that a rock layer is a single layer, which could be overlain or underlain by another layer, but anticlines and synclines are a series of rock layers.
Drag the appropriate labels to their respective targets.
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L to R - Anticline (top - Younger rock), Bottom (older rock), Right - Syncline
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Now, examine the outcrop in the Gigapan image again. Observe each side, or limb, of each fold. Compare the steepness of each limb's dip to determine whether the fold is symmetrical or asymmetrical.
Next, review the statements below, and indicate which are correct for the style of folding present in the Gigapan image.
Select all that apply.
answer
One side of the anticline dips more steeply than the other.
At least one of the folds in this outcrop is asymmetrical.
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Which of the following statements best describes the orientation of rock layers for a structural dome or structural basin?
answer
Rock layers wrap around a single point.
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If strike and dips symbols were placed on a map of a basin, which way would the dips point?
answer
Dips point down toward the center.
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Based on the ages of the rock layers in the cross-section, what kind of fold is in Figure 1? (Note: In map view, this feature would have a bull's-eye pattern.)
View Available Hint(s)
answer
basin
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What kind of structure is present in Figure 2?
View Available Hint(s)
answer
dome
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Which type of fold has rocks folding up in the middle?
answer
anticline
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Which of the following terms best describes the orientation of the fold in Figure 1?
answer
symmetrical
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Which fold orientation is visible in Figure 2?
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overturned
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Which kind of fold is visible in Figure 3?
answer
syncline
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What is the hinge line of a fold?
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line of maximum inflection that layers wrap around
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What is the orientation of a fold's hinge line with respect to the orientation of plunge?
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Hinge line is in the direction of plunge.
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How will the orientation of a plunging anticline's limbs change in the direction the fold is plunging?
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They will close to a point.
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What kind of fold is circled in Figure 1?
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nonplunging syncline
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Tensional forces normally cause which one of the following?
answer
normal faults
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The ________ in California is the boundary between the North American and Pacific plates.
answer
San Andreas strike-slip fault
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In thrust faulting, ________.
answer
the crust is shortened and thickened
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A graben is characterized by ________.
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A hanging wall block that has moved down between two normal faults
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In a normal fault ________.
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the hanging wall block above an inclined fault plane moves downward relative to the other block
break in rock caused by tension forces, where rock above the fault surface moves down relative to the rock below the fault surface
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A horst is ________.
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an uplifted block bounded by two normal faults
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Part A - Types of dip-slip faults
Sort the following features and descriptions according to the two dip-slip faults shown.
Drag the appropriate items to their respective bins.
answer
Diagram 1 - Hanging wall moves up relative to the footwall (see yellow on the right is higher than the left - the right is the hanging wall and the left is the footwall)
Reverse fault (when the top rock is going up instead of down, the top rock, aka hanging rock here).
Diagram 2 - the exact opposite of diagram 1. Hanging wall moves down relative to footwall, normal fault, caused by tensional forces.
So in other words the lower rock is pushing on the upper rock, forcing it to go down beneath it.
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What is a scarp?
answer
the trace of a fracture called a normal fault, where a portion of crust slides down the fault surface
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Alluvial fans are composed of material built up from sediment from the foot of the mountains to the valley floor. They are evidence that __________.
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Death Valley is a tectonically active region
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The Basin and Range consists of north-south trending mountain ranges separated by basins. What causes this distinct topography?
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Extension due to normal faulting causes valley floors to sink.
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The split cinder cone along the Southern Death Valley Fault is evidence that __________.
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The split cinder cone along the Southern Death Valley Fault is evidence that __________.
the Pacific and North American plates are moving alongside each other along strike-slip faults
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Which fault will see the hanging wall move down relative to the footwall?
answer
normal fault
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What kind of fault is visible in Figure 1?
answer
reverse fault
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What kind of force would create the fault in Figure 1?
answer
compression
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__________ faults combine elements of strike-slip and dip-slip motions.
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Oblique-slip
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The ________ are a geologically old mountain range folded and deformed during the Paleozoic.
answer
Appalachians in the eastern United States
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A good example of a present-day, passive continental margin is the ________.
answer
east coast of North America
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A(n) ________ is a thick accumulation of sediments and small, tectonic blocks formed of material scraped off a descending, lithospheric plate.
answer
accretionary-wedge complex
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Folded limestones that occur high in the Himalayas were originally deposited as sediments in a ________.
answer
marine basin between India and Eurasia
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Which of the following orogenies helped to create the Appalachian Mountains?
answer
Taconic, Acadian, and Alleghanian
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Which event marked the creation of the supercontinent Pangaea?
answer
The Iapetus Ocean closed during the Alleghanian Orogeny.
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Which of the Appalachian Mountain Belt Provinces are visible in the circled area of Figure 1?
answer
Valley and Ridge
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Which of the following geographic provinces is the newest addition to the North American continent?
answer
Coastal Plain
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Which mountain range marks the boundary between the Indian and Eurasian Plates?
answer
Himalayas
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What kind of tectonic boundary is currently responsible for creating the Himalayas?
answer
Continent-Continent Convergent Boundary
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What geologic features were created in the Eurasian Plate when India underthrust beneath it?
answer
thicker continental crust
thrust faults
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As India moves northward, China and Southeast Asia are being relocated to the east and southeast because of "escape tectonics." What feature is allowing them to "escape"?
answer
strike-slip faults
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When the Indian Plate collided with Eurasian Plate, why didn't it subduct?
answer
The Indian Plate is too buoyant.
The Indian Plate is too thick.
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A terrane is __________.
answer
a mass of rock that formed elsewhere and was added to a continent
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Which tectonic boundary is associated with the addition of terranes to a continent?
answer
convergent boundary
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What is the name of the process by which terranes are added to continents?
answer
accretion
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Using the map in Figure 1, determine which of the named terranes accreted earliest to North America.
answer
Yukon-Tanana
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The map in Figure 2 is a cross-section of the North American continent 600 million years ago and after the break-up of Pangaea approximately 200 million years ago. Which material(s) had been accreted to North America as terranes?
answer
Iapetus Ocean Island Arc and sediments, the Avalon Terrane, and a remnant of Africa
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Which of the following scenarios could result in the development of a compressional mountain belt?
answer
two landmasses collide
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Which geologic features would be present in compressional mountain belts? (Note: There may be more than one answer.)
answer
folds
thrust faults
intrusive igneous rocks
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Which of the following rocks are characteristic of compressional mountain building?
answer
schist
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Using the map provided in Figure 1, in which province would the Rocky Mountains of the United States be located?
answer
young mountain belts
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