PM 7 Origin of Mountains
Which letter in the graphic labels a symmetrical anticline?
A
What is a batholith, and in what modern tectonic setting are batholiths being generated?
A batholith is a massive pluton that crystallizes at depth within the crust. Batholiths are currently being generated within the North American Cordillera.
How are reverse faults different from thrust faults?
A reverse fault is steeper than a thrust fault; thrust faults have dips that are lower than 45 degrees.
How does the principle of isostatic adjustment account for the changes in the elevation of mountains?
As mountains erode to lower levels, the weight at that point in the crust decreases, causing the crust to rise. As this cycle of erosion and crustal rising continues, the mountain block approaches a normal crustal thickness.
Which correctly describe(s) brittle deformation and ductile deformation? Choose all that apply.
Both types of deformation are permanent. Brittle deformation describes a rock breaking as a result of stress, whereas ductile deformation describes a rock bending or folding as a result of stress.
Which of the following scenarios best describes the deformation that will occur in different parts of the crust?
Brittle deformation is dominant in the shallow crust; ductile deformation is dominant in the deep crust.
When the Indian Plate collided with Eurasian Plate, why didn't it subduct?
Choose all that apply. The Indian Plate is too thick. The Indian Plate is too buoyant.
If strike and dips symbols were placed on a map of a basin, which way would the dips point?
Dips point down toward the center.
How does mountain building at a volcanic island arc differ from mountain building at an Andean-style continental margin?
During island arc-type mountain building, an oceanic plate subducts beneath another oceanic plate, whereas during Andean-type mountain building, an oceanic plate subducts beneath a continental plate.
Which mountain range marks the boundary between the Indian and Eurasian Plates?
Himalayas
What is the orientation of a fold's hinge line with respect to the orientation of plunge?
Hinge line is in the direction of plunge.
Based on what you learned in the video, which of the following statements regarding joints is true?
Joints are fractures in rocks where very little to no movement has occurred.
Imagine a fold has been eroded to a flat surface. In general, how would you know whether this fold is plunging?
Nonplunging folds look like straight lines at the surface, and plunging folds look like wavy lines.
Which type of fault is associated with fault-block mountains?
Normal fault
__________ faults combine elements of strike-slip and dip-slip motions.
Oblique-slip
What is the difference between strain and stress?
Strain is the change in rock shape that results from stress, which is the force that deforms the rock.
Which of the following orogenies helped to create the Appalachian Mountains?
Taconic, Acadian, and Alleghanian
Which correctly describes a passive continental margin?
The presence of an extensive platform of sediments and sedimentary rocks
If the Rocky Mountains were eroded, what would happen to the roots of the mountains?
The roots would rebound upward.
Imagine you are out in the field and have to sketch and label the view below. Based on observations from the previous photo, which of the following sketches is the most accurate?
The sketch shows an older stratum made predominantly of sandstones surrounded by poorly exposed areas. The bedding is oriented along the slopes. A younger stratum made predominantly of carbonates towers at the background.
How will the orientation of a plunging anticline's limbs change in the direction the fold is plunging?
They will close to a point.
What produces plunging folds?
a combination of folding and tilting
What is a syncline?
a fold shaped like a right-side-up U
Which type of fold has rocks folding up in the middle?
anticline
Large circular downwarped structures are called ________.
basins
Which type of force causes folding?
compressional force
What kind of structure is present in Figure 2?
dome
Burial of rocks increases the confining pressure so that deeply buried rocks are more likely to ________ than shallow rocks.
fold
Which of the following is an example of how rocks will respond to compressional stress?
folding reverse faulting
In a monocline, one of the limbs of the fold ________.
is horizontal
What kind of fold is circled in Figure 1?
nonplunging syncline
Grabens are formed by what type of faulting?
normal
Which fault will see the hanging wall move down relative to the footwall?
normal fault
Which fold orientation is visible in Figure 2?
overturned
What is the modern theory for orogenesis?
plate tectonics theory
What kind of fault is visible in Figure 1?
reverse fault
Use the figure below to answer the following question. In the figure, the stress on block 'Z' is ________.
shear
The San Andreas Fault in California and the Alpine Fault in New Zealand are examples of ________.
strike-slip faults
Which kind of fold is visible in Figure 3?
syncline
Batholiths, such as those that make up the Sierra Nevada Mountains of California, form at great depth in the crust. How could they have been exposed at the surface?
uplift and erosion
What kind of tectonic boundary is currently responsible for creating the Himalayas?
Continent-Continent Convergent Boundary
In the plate tectonics model, which type(s) of plate boundary(ies) is(are) most directly associated with Earth's major mountain belts?
Convergent boundary
What is orogenesis?
The collection of processes that produce a mountain belt
What is isostasy?
The concept that the crust floats in gravitational balance in the mantle.
Using what you know about isostasy, how would the crust behave if a large glacier were removed?
The crust would move up in elevation.
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.)
basin
The Appalachians were formed by three phases of ________ orogeny.
collisional
What kind of force would create the fault in Figure 1?
compression
Use the figure below to answer the following question. In the figure, the stress on block 'X' is ________.
compressional
What is the hinge line of a fold?
line of maximum inflection that layers wrap around
Use the figure below to answer the following question. In the figure, which of the deformations appears most similar to what might be expected along a divergent plate boundary?
Y
Use the figure below to answer the following question. In the figure, which of the deformations appears most similar to what might be expected along a transform plate boundary?
Z
What is an anticline?
a fold shaped like an upside-down U
What does the term plunging fold mean?
a fold that is tilted down into Earth
A transform fault is ________.
a strike-slip fault that forms the boundary between tectonic plates
In a(n) ________ fault, the hanging wall block moves up with respect to the footwall block.
reverse
The concepts of "stress" and "strain" are related because ________.
"stress" causes "strain"
The parking lot of Calico Ghost Town in southern California is a great place to study folds due to excellent exposure and easy access. The series of questions below focuses on types of folds and their components. The photo below shows a fold train, composed of two folds, and their features outlined by orange and red lines. Drag the appropriate labels to their respective targets. Not all labels will be used.
Anticline Syncline Shared limb Axial Plane
Which of the following geographic provinces is the newest addition to the North American continent?
Coastal Plain
What is rock deformation, and how might a rock body change during deformation?
Deformation is a rock's reaction to stress, which can cause a rock to change its shape or position.
Which distinguish(es) between anticlines and synclines, domes and basins, and anticlines and domes? Choose all that apply.
Folded rock layers in anticlines arch upward, whereas folded rock layers in synclines arch downward. Folded rock layers in domes upwarp, whereas folded rock layers in basins downwarp. Anticlines have hinge lines, whereas domes are roughly circular when viewed from above.
_____ is the principle that explains why materials uplift to a certain elevation.
Isostasy
How do monoclines form?
Movement along a steep fault in basement rock pushes up a portion of the ductile rock layers above it.
Which of the following statements best describes the orientation of rock layers for a structural dome or structural basin?
Rock layers wrap around a single point.
Imagine a syncline has been eroded to a flat surface. How would the rock age change as you walked across that flat surface?
Rocks would be oldest on the edges and youngest in the middle.
Imagine an anticline has been eroded to a flat surface. How would the rock age change as you walked across that flat surface?
Rocks would be youngest on the edges and oldest in the middle.
In this photo, you can see sedimentary rocks that have been exposed by weathering and erosion. Yellow lines show curved light-colored sandstone beds that are exposed in canyons cut into the anticline. Orange lines point out red- to orange-colored dipping sedimentary beds that have been eroded from the upper part of the anticline. Concentrate on the series of events that led to the formation and exposure of this anticline. Rank the following events in order from OLDEST to YOUNGEST in age.
Sediments are deposited in a horizontal orientation. The sediments are buried and lithified into sedimentary rock. Compressional forces cause the sedimentary rocks to bend into an anticline. Processes of weathering and erosion expose the interior of the anticline.
Which event marked the creation of the supercontinent Pangaea?
The Iapetus Ocean closed during the Alleghanian Orogeny.
Below are a series of sketches that outline both the fracture and sedimentary rock layers. The key includes information from each sketch. Select the correct sketch and corresponding key below.
The figure shows a photo of an outcrop with several additional lines indicated. Yellow parallel lines are drawn along the rock layers and stop at a red line drawn along the huge crack that is almost perpendicular to the yellow lines. Yellow lines. Yellow lines located to the left of the crack are shifted downward with respect to the yellow lines located to the right of the crack. Two half-arrows, an upward and a downward one, are drawn to the right and to the left of the red line, respectively. There is an inset with the key. It is said there that yellow lines represent sedimentary rock layers and the red line represents a fault, with arrows showing the direction of offset.
Which of the following images best describes how a rock in the deep crust would be deformed as a result of shear stress?
The figure shows a side section of a rock. Rocks are subjected to tectonic forces that are parallel, but in opposite directions. The right part is a little raised. There are no any fractures and fissures.
Where and how might magma be generated in a newly formed collisional mountain belt?
The magma intrudes the crustal rocks along the continental margin after an ocean basin closes.
The photo below shows a geologist standing in front of an outcrop of thick sandstone beds. Using what you learned in the video about faults and joints, classify the statements according to whether they are "true," "false," or "not enough information to tell". Drag the appropriate items to their respective bins.
True The cracks in the sedimentary rocks are joints. The fractures are a result of brittle deformation. False The sedimentary rock shown here has been significantly displaced. No cracks exist in this outcrop. Not enough information to tell
Which of the Appalachian Mountain Belt Provinces are visible in the circled area of Figure 1?
Valley and Ridge
When subjected to a differential stress, a very "brittle" material, like glass, will ________.
deform by breaking or elastic bending
Use the figure below to answer the following question. The material in the figure was ________ when the folding occurred.
ductile
Folds are an example of ________.
ductile deformation
The higher the temperature, the more likely it is that a rock will deform ________.
ductilely
Most active faults pose a risk to society because they can potentially produce ________.
earthquakes
_____ are shown in the photo above. They are characterized by _____ sedimentary rock layers.
faults, discontinuous
Monoclines, anticlines, synclines and domes are all examples of ________.
foliation
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"?
strike-slip faults
The boundary between two terranes or two continents that have collided is called a ________.
suture
Which of the following terms best describes the orientation of the fold in Figure 1?
symmetrical
Which tectonic stress will result in a lengthening of the crust?
tension
Use the figure below to answer the following question. In the figure, the stress on block 'Y' is ________.
tensional
What geologic features were created in the Eurasian Plate when India underthrust beneath it?
thrust faults thicker continental crust
