GEOL Module 8 Homework
When did Pangea begin to break into smaller fragments?
180 million years ago
How far apart are points A and B in meters? If the fault has been moving at 3.4 cm/yr, how long ago were the two points together?
200 m; 5900 years
Select the Ruler tool and set it to Path. What is the distance along the San Andreas Fault between the two locations in kilometers, and what has been the rate of movement on the fault in cm/yr over the past 23 million years?
310 km; 1.35 cm/yr
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.
The Appalachian Mountains in North America were formed by a continent-continent collision in the Paleozoic, and are an example of a(n) ________-type orogeny.
Alpine
What is an accretionary wedge, and how does it form?
An accretionary wedge is an accumulation of deformed, thrust-faulted sediments and scraps of ocean crust. This wedge is plastered against the edge of the overriding plate from the subducting plate.
Which statement(s) below distinguish(es) between anticlines and synclines, domes and basins, and anticlines and domes? Select all that apply.
Anticlines have hingelines, whereas domes are roughly circular when viewed from above. 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.
Now we can apply our observations to considering how this mountain range was built. Review the statements below, and select the best answer regarding the geologic history of mountain building forces in the Canadian Rockies.
Compressional deformation dominates the Canadian Rockies at the regional scale.
What kind of tectonic boundary is currently responsible for creating the Himalayas?
Continent-Continent Convergent Boundary
Which mountain range marks the boundary between the Indian and Eurasian Plates?
Himalayas
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?
Iapetus Ocean Island Arc and sediments, the Avalon Terrane, and a remnant of Africa
_____ is the principle that explains why materials uplift to a certain elevation.
Isostasy
Double-click the Fault Trace placemark. Which of the following statements about the San Andreas Fault is correct?
It is a right-lateral strike-slip fault caused by shear stress.
Which best describes the difference between a joint and a fault?
Motion occurs along faults, but not joints.
How do mountainous regions experience gravitational collapse?
Mountains that have risen to extreme heights experience ductile spreading at depth and normal faulting as well as subsidence in the upper, brittle portion of Earth's crust.
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.
________ faults form in response to horizontal, tensional stresses that stretch or elongate the rocks.
Normal
Which of the following examples best illustrates the effects of ductile deformation?
Rocks along a convergent plate boundary are subjected to compressive force for millions of years and are permanently folded.
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.
Which of the below choices supports the concept of crustal uplift?
Seismic tomography has shown a superplume centered below the southern tip of Africa. This is thought to explain the high topography of the area, which consists of an expansive plateau with an elevation of 1500 kilometers.
At which types of plate boundaries do the three types of differential stress occur?
Shear stress occurs at transform boundaries, compressional stress occurs at convergent boundaries, and tensional stress occurs at divergent boundaries.
Which of the descriptions below accurately describe(s) the various types of differential stress? Select all that apply.
Shear stress, which moves one part of a rock body past another, changes rock shape and can break rocks apart. Compressional stress, which squeezes rock, generally shortens rocks horizontally and thickens them. Tensional stress, which pulls rock apart in opposite directions, horizontally stretches and lengthens rock bodies.
Why are terranes added to continental margins, rather than subducting under them?
Terranes are too buoyant to subduct.
When viewed from the air, the Bighorn River cuts across the Sheep Mountain anticline. As Sheep Mountain is a topographic high and barrier to streamflow, how was the river able to establish itself and eventually erode through the anticline?
The Ancestral Bighorn River established a course over the landscape while the anticline was still buried at depth.
When the Indian Plate collided with Eurasian Plate, why didn't it subduct?
The Indian Plate is too thick. The Indian Plate is too buoyant.
Using what you know about isostasy, how would the crust behave if a large glacier were removed?
The crust would move up in elevation.
Why was the continental crust of Asia deformed more than the continental crust of India during the formation of the Himalayas?
The edge of the continental crust of Asia was an active margin and thus was more easily deformed than the passive continental margin of India that consisted of a thick plateau of sedimentary rocks.
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.
Which of the following statements about terranes is most accurate?
The margins of many continents have grown through the accretion of terranes.
If the Rocky Mountains were eroded, what would happen to the roots of the mountains?
The roots would rebound upward.
Where do the youngest rocks in an eroded basin outcrop? Select all that apply.
The youngest rocks of a basin are on top of all the other rock layers in the center of the basin in cross-section. In top view, the youngest rocks of a basin are in the middle of the basin.
Match the orientation line images below with positions of the folds located at A, B, and C on the image of the Mt. Kidd outcrop below. The orientation lines show the fold limbs (solid lines) relative to the axial plane of the fold (dotted line).
This outcropping shows great examples of folds that can be characterized as both anticlines and synclines.
How does the plate tectonics theory help explain the existence of fossil marine life in rocks on top of compressional mountains?
When two plates collide at their continental margins, the deformable seaward rock containing marine organisms crumples up to the top of the resulting mountains.
Using the map in Figure 1, determine which of the named terranes accreted earliest to North America.
Yukon-Tanana
What does a turbidite sequence consist of?
a blanket of sand overlain by a sheet of mud
What produces plunging folds?
a combination of folding and tilting
What is a syncline?
a fold shaped like a right-side-up U
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 terrane is __________.
a mass of rock that formed elsewhere and was added to a continent
What is a terrane?
a slice of lithosphere that has been added to the margin of a continent during plate collision
What is the name of the process by which terranes are added to continents?
accretion
Return to the Gigapan image, and study the area indicated in the thumbnail below. What type of structural deformation is present in the outcrop at this location?
an asymmetrical fold
Which of the following will increase the likelihood of ductile deformation in a rock? Choose all that apply.
an increase in rock temperature an increase in confining pressure
A horst is ________.
an uplifted block bounded by two normal faults
Large circular downwarped structures are called ________.
basins
Which type of force causes folding?
compressional force
Terrane accretion generally occurs along a ________ boundary between a continental plate and an oceanic plate.
convergent
Which tectonic boundary is associated with the addition of terranes to a continent?
convergent boundary
The Black Hills of South Dakota are a good example of a(n) ________.
dome
Folds form as a result of ________.
ductile deformation
A good example of a present-day, passive continental margin is the ________.
east coast of North America
The anticline that makes up Sheep Mountain is rather small and restricted in extent. What other local feature might be present that would constrain this fold to a small geographic area?
faults in the basement rock beneath the anticline.
Which process can decrease the height of a mountain?
gravitational collapse
Which of the characteristics below make(s) a rock very strong as opposed to very deformable? Select all that apply.
having a very low temperature being a metamorphic rock composed of quartz having a very high confining pressure having force suddenly applied to it
Where does most terrane accretion occur?
in association with a continental-oceanic subduction zone
Examine the words and/or phrases below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern. reverse fault joint normal fault thrust fault
joint
What are stromatolites?
mats of blue-green algae that grew in mounds up from the sea floor
Rock deformation mostly occurs ________.
near the centers of plates
Which type of fault is associated with fault-block mountains?
normal fault
A series of synclines and anticlines is oriented with the hinge lines of the folds trending east-west. From which directions did the force come to create these folds?
north-south
The term ________ refers specifically to geologic mountain building.
orogenesis
A(n) ________ fault has little or no vertical movements of the two blocks.
strike slip
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
What caused metamorphism to occur in the Blue Ridge District during the Alleghanian Orogeny?
strong differential stress generated by compressional stress as rocks were thrust westward
Which of the following processes resulted in the deformation of sedimentary units in the American West during the Jurassic Period?
subduction of the Farallon plate beneath the North American plate
What is the geologic term for folded rocks with the bend at the bottom?
syncline
The mountains and valleys of the Basin and Range Province of the western United States formed in response to ________.
tensional stresses and normal-fault movements
What is orogenesis?
the collection of processes that produce a mountain belt
Which of the following are mountain-building processes? Choose all that apply.
the collision of two pieces of continental crust oceanic lithosphere subducting beneath continental crust the rifting of the continental crust oceanic lithosphere subducting beneath oceanic crust
Isostasy refers to ________.
the concept that rocks of the crust and upper mantle are floating in gravitational balance
In thrust faulting, ________.
the crust is shortened and thickened
In a normal fault, ________.
the hanging wall block moves downward relative to the other block
What geologic features were created in the Eurasian Plate when India underthrust beneath it?
thicker continental crust thrust faults
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
Which one of the following is an example of an isostatic movement?
uplift of areas recently covered by thick, continental ice sheets
