Geol 101 Online HW ch.11

When a rock is under undue stress and fractures but there is no movement to either side of the fracture, the feature is a called a __________. If, however, there is movement, it is called a ______________.

1) Joint 2) Fault

Geologists often look at various characteristics of terrane to determine whether it is accreted or not. Terranes formed in different places will have different geologic histories and mineralogies, animal and plant life, and magnetic signatures. After accretion, which tools could a geologist use to differentiate between a terrane and the continent onto which it accreted? (Select two that apply.)

1) Look for fossils that are distinct from those of the continent. 2) Look at the rock types and determine if they are distinctly different from the continent.

Which of the following is an example of how rocks will respond to compressional stress? (Check all that apply.)

1) Reverse faulting 2) Folding

When the Indian Plate collided with Eurasian Plate, why didn't it subduct? (Choose all that apply.)

1) The Indian Plate is too buoyant. 2) The Indian Plate is too thick.

What geologic features were created in the Eurasian Plate when India underthrust beneath it? (Choose all that apply.)

1) Thicker continental crust 2) Thrust faults

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

Anticline

A portion of a fold that appears to arch upwards, with the limbs of the fold dipping away from one another.

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

If a rock undergoes folding and is compressed to form an upward arch, this is a(n) ___________ type fold

Anticline

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.) (Image: 1 million years in center, 10 million years in the outer edge)

Basin

Imagine two rocks. Under enough stress, rock A will experience plastic strain, whereas rock B will experience brittle strain. Which of the following statements about rocks A and B is true?

Both rock A and rock B will experience elastic strain before plastic or brittle strain sets in.

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.

Joints

Brittle deformations (fractures) in a rock along which there has been no movement.

Faults

Brittle deformations (fractures) in a rock mass along which movement has occurred.

Which of the following geographic provinces is the newest addition to the North American continent?

Coastal Plain

Which type of force causes folding?

Compressional force

Which type of force is responsible for reverse fault formation?

Compressional force

What kind of tectonic boundary is currently responsible for creating the Himalayas?

Continent-Continent Convergent Boundary

Which tectonic boundary is associated with the addition of terranes to a continent?

Convergent boundary

Thrust faults

Dip-slip faults where the dip of the fault is less than 45∘∘, causing the movement of the hanging wall to be nearly horizontal to the fault surface.

Normal faults

Dip-slip faults where the hanging wall block moves down relative to the footwall block, and they occur when the crust is extended, or lengthened.

Reverse faults

Dip-slip faults where the hanging wall block moves up relative to the footwall block, and they occur during compressive shortening of the crust.

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.

What kind of structure is present in Figure 2? (Image: Circle, with layers moving downward on side, underground)

Dome

Folds

Ductile deformations where a bent rock layer or series of layers that were originally horizontal are subsequently deformed.

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.

_____ are shown in the photo above. They are characterized by _____ sedimentary rock layers.

Faults, discontinuous

Tensional stress

Forces pull a body of rock outward, resulting in elongation of the body.

Compressional stress

Forces push a body of rock inward, resulting in compression of the body.

What is a fault?

Fractures along which rocks move

Using the map of present-day oceanic plateaus and other submerged crustal fragments below, determine which feature is most likely to be accreted onto a continent. Use the information on the map above to guide you with regards to active margins.

Galapagos Rise

Which mountain range marks the boundary between the Indian and Eurasian Plates?

Himalayas

Where does most terrane accretion occur?

In association with a continental-oceanic subduction zone

_____ is the principle that explains why materials uplift to a certain elevation.

Isostasy

Spectacular joints can be observed in the Alabama Hills of Owens Valley, California. The joints occur in granite bedrock. 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.

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?

Lapetus Ocean Island Arc and sediments, the Avalon Terrane, and a remnant of Africa

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.

Large rifts or valleys, which can often have very large _________ faults, are created by tensional forces.

Normal

Shear stress

Opposing forces push different ends of a body of rock in opposite directions, resulting in displacement of one end of the body with respect to the other.

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.

Which type of force is responsible for normal strike-slip formation?

Shear force

Which type of fault has NO vertical motion of rocks associated with it?

Strike-slip fault

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

A trough, or downward fold, called a(n) ____________ is formed when a rock is deformed through folding.

Syncline

Which of the following orogenies helped to create the Appalachian Mountains?

Taconic, Acadian, and Alleghanian

Which tectonic stress will result in a lengthening of the crust?

Tension

Which type of force is responsible for normal fault formation?

Tensional force

Why are terranes added to continental margins, rather than subducting under them?

Terranes are too buoyant to subduct.

Which event marked the creation of the supercontinent Pangaea?

The Iapetus Ocean closed during the Alleghanian Orogeny.

What is strain?

The amount of deformation that results from an applied force

Using what you know about isostasy, how would the crust behave if a large glacier were removed?

The crust would move up in elevation.

What are rocks below and above a fault called?

The footwall below and the hanging wall above

What is stress?

The force exerted to cause deformation

Which of the following statements about terranes is most accurate?

The margins of many continents have grown through the accretion of terranes.

Syncline

The part of the fold where the limbs dip towards one another, similar to a trough.

What happens when stress exceeds a plastic rock's yield strength?

The rock will experience flow.

What happens when stress exceeds a brittle rock's yield strength?

The rock will experience fracture.

Elastic deformation

The rock will return to nearly its original size and shape when the stress is removed.

If the Rocky Mountains were eroded, what would happen to the roots of the mountains?

The roots would rebound upward.

Imagine two rocks. Rock A is weaker than rock B. Which of the following statements about rocks A and B is true?

The yield strength of rock A is lower than that of rock B.

Monocline

There's just one limb of a fold

Brittle deformation

This involves the fracturing of rock and is associated with rocks near the surface.

Ductile deformation

This is a type of solid state flow that produces a change in the size and shape of a rock body without fracturing. It occurs at depths where temperatures and confining pressures are high.

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 of the Appalachian Mountain Belt Provinces are visible in the circled area of Figure 1?

Valley and Ridge

Using the map in Figure 1, determine which of the named terranes accreted earliest to North America.

Yukon-Tanana (the one closest to the coast/land of canada)