GEOL 1403 Chapter 2 Plate Tetonics

A very long-lived magma source located deep in the mantle is called a(n) __________.

hot spot

According to the plate tectonics model, the rigid ________ moves over top of the weaker ________.

lithosphere, asthenosphere

Which of the following features results from continent-to-continent convergence?

mountain belt

In what direction is the city of Los Angeles moving relative to the North American plate?

northwest

What type of region is the modern-day Red Sea?

A rift zone that may eventually open into a major ocean if Arabia and Africa continue to separate

Which of the following statements applies to the asthenosphere, but not the lithosphere?

A zone in the upper mantle that deforms by plastic flowage

Which of the following statements about the mid-ocean ridge is true?

All of these statements are true.: - The mid-ocean ridge is the longest topographic feature on Earth's surface. - The mid-ocean ridge winds through all major ocean basins. - The mid-ocean ridge is where oceanic lithosphere is formed.

What causes the linear patterns associated with paleomagnetism on either side of mid-oceanic ridges?

Normal and reversed magnetized strips roughly parallel to the ridge

Part D What is the main material being subducted at an ocean-continent convergent boundary?

Oceanic lithosphere

Where are most transform faults found?

on the ocean floor

Part B Oceanic lithosphere contains oceanic crust and the __________.

outermost part of mantle beneath the oceanic crust

Which of the following ideas about continents and ocean basins is correct?

Oceanic plate material is formed at divergent plate boundaries and consumed at convergent plate boundaries.

How does the age of oceanic lithosphere relate to the angle of its subduction?

Older oceanic lithosphere subducts at a steeper angle than younger oceanic lithosphere.

According to Figure 2.33 in your textbook, which of the following plates is moving at the fastest rate?

Pacific plate

Which of the following is not evidence supporting the theory of plate tectonics?

Shifting plates were caused by changes in the Moon's orbit.

What does the plate tectonic theory state?

The lithosphere of Earth is divided into rigid pieces that move relative to one another.

Why is the study of paleomagnetism possible?

The magnetic minerals in a cooling lava point toward the north magnetic pole.

What evidence did the Deep Sea Drilling Project find about the dates of rocks in the ocean basins?

The ocean basins are relatively young; most ocean basin rocks and sediments are Cretaceous or younger in age.

Which of the following is true of the rocks of the seafloor?

The oldest rocks of the seafloor are younger than the oldest rocks on the continents.

Part C What did the maps of the ocean floor produced by Bruce Heezen and Marie Tharp reveal about seafloor topography?

There are ridges in the middle of the ocean basin floors.

After World War II, what was discovered about the ocean floor?

There is no oceanic crust older than 180 million years old.

Part D Why did Heezen and Tharp have to do "inspired guessing" when creating their maps of the ocean floor?

There were gaps in the data that were used to make the map because the tracks of the ships collecting the data were widely spaced.

Which of the following paleoclimatic evidence supports the idea of the late Paleozoic supercontinent in the Southern Hemisphere?

Tillites (rocks formed by glaciers) in South Africa and South America

A transform plate boundary is characterized by __________.

a deep, vertical fault along which two plates slide past one another in opposite directions

What tectonic feature are the Aleutian Islands of Alaska?

a volcanic island arc

Which force contributes the most to plate motion?

slab pull

What is the typical rate of seafloor spreading in the Atlantic Ocean?

2 centimeters per year

What is the temperature above which magnetite loses its magnetization?

800°C

Part C How is the thickness of the lithosphere going to change as it moves away from a divergent plate boundary?

Lithosphere will thicken as more mantle is added.

What is a modern example of an active continental rift?

East African Rift

Part B Seafloor depth was first determined by what remote sensing technology?

Echo sounder

Glacial striations (scratches) indicate the direction of past ice movement. What do the glacial striations found in South America, Africa, India, Antarctica, and Australia, when these continents are placed together in their pre-drift Pangaea positions, indicate?

Glacial striations indicate that ice movement radiated away from a central point, similar to today's continental ice sheets.

What was the name of the fossil flora that grew on Pangaea during the late Paleozoic?

Glossopteris

How do the fossil remains of Mesosaurus support Alfred Wegener's hypothesis?

Mesosaurus was a freshwater reptile whose fossils are found in Africa and South America.

Part A - Types of subduction zones There are two types of subduction zones: Mariana-type subduction zones and Peru-Chile-type subduction zones. Mariana-type subduction zones occur wherever cold and dense oceanic lithosphere spontaneously subducts into the asthenosphere, as described in the introduction. Peru-Chile-type subduction zones occur wherever oceanic lithosphere is forced prematurely into the asthenosphere by the compressional forces that occur at convergent plate boundaries as shown in the figure below. Subducting slabs in Mariana-type subduction zones typically descend into the asthenosphere at steeper angles than subducting slabs in Peru-Chile-type subduction zones because they are more dense. Rank the density of the lithosphere at points A, B, and C.

Highest Density: A (Mariana-type) C (Peru-Chile type subduction slabs) Lowest Density: B (Peru-Chile type)

What process is evident at oceanic trenches?

Sinking of oceanic lithosphere into the mantle at a subduction zone

What does the Hawaiian Island-Emperor Seamount chain indicate about past movement of the Pacific plate?

The Pacific plate changed direction of movement about 50 million years ago.

The San Andreas Fault that runs through the state of California is the boundary between the Pacific Plate to the west and the North American Plate to the east. The Pacific Plate is moving north relative to the North American Plate, so this is a transform plate boundary, where plates slide horizontally past one another. It is estimated that, with continued plate movement, Los Angeles and San Francisco will be at the same latitude in about 10 million years. Part A - California and Transform Fault Boundaries Some predict that California will eventually sink into the ocean. Is this hypothesis consistent with the theory of plate tectonics and with the type of plate boundary that is present in California? Explain.

The San Andreas Fault represents the transform boundary between two major plates of the Earth's crust (North American and Pacific Plates) which causes strike-slip earthquakes. California will not sink but move laterally along the west coast in the future.

Part E What are two differences between oceanic crust and continental crust?

The continental crust is thicker and less dense than oceanic crust.

Which two scientists proved that a symmetrical magnetic pattern existed in seafloor basalts and related those stripes to spreading at a mid-oceanic ridge?

Vine and Matthews

Complete this statement using the choices below. With regards to ancient climates, Wegener's continental drift hypothesis states that 300 million years ago...

areas in North America, northern Africa, Europe, and Asia produced tropical swamps along the equator while areas in South America, Africa, India, Australia, and Antarctica were glaciated at the South Pole.

What is the name of the hypothesis developed by Alfred Wegener that later gave way to the theory of plate tectonics?

continental drift

What is the typical rate of seafloor spreading?

2 to 15 centimeters per year

When did the supercontinent of Pangaea begin to break apart?

200 million years ago

What causes the volcanoes and deep valleys of East Africa?

A continental rift along parts of the African continent beginning to slowly separate

What type of boundary occurs along the Aleutian Islands in the North Pacific?

A convergent boundary on a volcanic arc above the northward-subducting Pacific plate

What type of plate boundary is usually associated with pull-apart rift zones?

A divergent plate boundary

Part A Which of the following is a layer of the Earth that is classified NOT by composition, but by physical properties?

Asthenosphere

Which of the following was never proposed as evidence supporting the existence of Pangaea?

Islands along the Mid-Atlantic Ridge with rocks dating back from 542 million to 2500 million years ago

Which of the following is not considered one of the seven "major" lithospheric plates?

Juan de Fuca plate

Part A - The Characteristics of Convergent Boundaries Refer to the images in the three scenarios below that show different types of convergent plate boundaries and label items accordingly.

Left: - Oceanic-continental plate convergence - creates abundant volcanic activity on the overriding continental plate Middle: - oceanic-oceanic convergence - creates volcanic activities resulting in volcanoes growing up from the ocean floor Right: - continent-continent convergence - doesn't create volcanic activity

Part A - Types of convergent plate boundaries Identify each type of convergent plate boundary.

Left: Oceanic-continental plate convergence -When an oceanic plate converges with a continental plate, the oceanic plate, being denser, subducts to form volcanic mountains. Middle: Oceanic-oceanic plate convergence -When two oceanic plates converge, the denser of the two subducts into the mantle. The subduction results in the partial melting of lithospheric rock above the area of subduction, leading to the formation of volcanoes. Right: Continental-continental plate convergence -When two continental plates converge, neither of them subducts as they have a density that is much lower than the mantle, resulting in the formation of a collisional mountain chain.

Part B - Geologic features formed due to convergent plate boundaries Depending on the type of plate convergence, different features could result. Examples of these features include volcanic island arcs, continental volcanic arcs, and a collisional mountain chain.

Left: Volcanic Island Arcs Middle: Continental Volcanic Arcs Right: Collisional Mountain Chain

Which of the following statements is true?

Paleomagnetic stripes on the seafloor are mirror images on either side of the mid-ocean ridge.

The former, late Paleozoic supercontinent is known as __________.

Pangaea

Part E As Heezen and Tharp interpreted the ocean depth data, they identified what unusual feature that hinted at continental drift?

The oceanic ridges have a cleft, or rift, in the middle rather than a peak.

Part A What prompted the first widespread mapping of the ocean floor?

The importance of submarine warfare during World War II

Which of the following pieces of evidence supports the plate tectonic theory?

The stripe patterns of high- and low-intensity magnetism are mirror images on both sides of an oceanic ridge

Part B - The features of subduction zones The main features of subduction zones are deep-sea trenches, volcanic arcs, batholiths, accretionary wedges, forearc basins, and back-arc basins. Deep-sea trenches are where the oceanic lithosphere bends as it descends into the asthenosphere. Volcanic arcs are produced by magmas generated from the partial melting of a subducting slab. Batholiths are accumulations of rising magma plutons that harden before they reach Earth's surface. They usually are formed underneath volcanic arcs, but as a result of uplifiting and erosion they can appear on Earth's surface. Accretionary wedges are accumulations of sediment that are scraped off a subducting plate as it grinds past its overriding plate. Forearc basins are the low-lying regions composed of relatively undeformed layers of sediment and sedimentary rocks. They are usually formed next to accretionary wedges. Back-arc basins are formed when a subducting slab increases its angle of descent, which causes its deep-sea trench to migrate away from the overriding plate. This allows the overriding plate to stretch out, which creates a region of thin lithosphere called the back-arc basin. The names of forearc and back-arc basins refer to their position with respect to a volcanic arc. Forearc basins lie in front of volcanic arcs, while back-arc basins lie beyond volcanic arcs. Label the diagrams below with the appropriate subduction zone feature.

Top left Picture- Deep-sea trenches are where the oceanic lithosphere bends as it descends into the asthenosphere. (Group 1) Volcanic arcs are produced by magmas generated from the partial melting of a subducting slab. (Group 1) Top Right Picture- Back-arc basins are formed when a subducting slab increases its angle of descent, which causes its deep-sea trench to migrate away from the overriding plate. This allows the overriding plate to stretch out, which creates a region of thin lithosphere called the back-arc basin. (Group 2) Bottom Picture- Batholiths are accumulations of rising magma plutons that harden before they reach Earth's surface. They usually are formed underneath volcanic arcs, but as a result of uplifting and erosion, they can appear on Earth's surface. (Group 1) Accretionary wedges are accumulations of sediment that are scraped off a subducting plate as it grinds past its overriding plate. (Group 1) Forearc basins are the low-lying regions composed of relatively undeformed layers of sediment and sedimentary rocks. They are usually formed next to accretionary wedges. (Group 2)

The volcanoes and deep valleys of east Africa are related to a ________.

continental rift along which parts of the African continent are beginning to slowly separate

Which type of plate boundary forms a continental volcanic arc?

convergent plate boundary between one oceanic and one continental plate

Which type of plate boundary occurs where two plates move apart, resulting in upwelling and partial melting of hot material from the mantle?

divergent boundary

Which of the below is NOT a technique used when studying plate motion?

exploring oceanic crust by deep sea diving

In what direction was the Pacific plate moving while the Hawaiian Islands were forming?

to the northwest