GEOL1030 Ch. 4: Plate Tectonics

What has the average rate of spreading along the Mid-Atlantic Ridge (along 20° S, from approximately 14° W to 10.3° W) been during the past 10 million years in centimeters per year?

1.9 cm/yr

Which of the following is the oldest oceanic crust?

180-280 m.y. at 37 ° N, 19° E

What is a typical rate for seafloor spreading?

2 cm/yr

Oceanic ridges represent ________ percent of the earth's surface.

20

Which of the following locations shows signs of having spread the fastest during the period 60-70 m.y.a. (million years ago), and how many kilometers of new crust were formed during that period?

7° S, 77° E, 590 km measured north-south

What was the rate of spreading 40-50 m.y.a. on the Nazca Plate off La Paz from 24.5° S, 80° W to 21° S, 72.6° W?

8.5 cm/yr

What has the average rate of spreading in the Pacific, along 20° S from approximately 121° W to 104° W, been during the past 10 million years?

8.6 cm/yr

What is a scientific revolution?

A major breakthrough discovery that alters scientists' view on how the earth works

What is a hot spot?

An area of volcanism created by a mantle plume

At which type of convergent plate boundary did the Himalaya mountain belt form and why?

At a continental-continental convergent boundary because the two continental plates buckled and thickened vertically when they collided

Where does new lithosphere form?

At divergent plate boundaries

Which ocean formed as a direct result of the breakup of Pangaea?

Atlantic

How did core samples drilled from various locations in the ocean floor support the concept of seafloor spreading?

Cores containing younger sediment were located closer to the ridge crest than were cores containing older sediment, meaning that older material is continuously being pushed away from the ridge.

Which one of the following is an important fundamental assumption underlying the plate tectonic theory?

Earth's surface area has been essentially constant over time.

Which of the following locations is a modern-day example of an active continental rift?

East Africa and the Red Sea

Which supercontinent contained Africa and South America?

Gondwanaland

________ is the youngest island of the Hawaiian Island chain.

Hawaii

Where is continental rifting currently taking place?

In the East African Rift Valley

________ was (were) never proposed as evidence supporting the existence of Pangaea.

Islands of Precambrian rocks along the Mid-Atlantic Ridge

What was the main view of how the world worked geologically prior to the 1960s?

It was generally believed that mountains were produced by vertical forces.

What were the names of the two smaller super continents that formed when Pangaea broke apart?

Laurasia and Gondwanaland

Why do scientists think that lithosphere has to be destroyed somewhere on or in the earth?

Lithosphere is created at divergent boundaries and the earth is not getting any larger.

What happens to the lithosphere at transform plate boundaries?

Lithosphere is neither destroyed nor created, simply maintained or conserved.

What do you think will happen to the location of Los Angeles with continued activity along the San Andreas Fault over a long time span?

Los Angeles will slide to the northwest.

Which of the following statements explains why the presence of Mesosaurus in both South America and Africa supports the continental drift hypothesis?

Mesosaurus was a freshwater aquatic reptile with fossil remains in both South America and Africa.

Which of the following statements about tectonic plates is true?

Most tectonic plates contain both oceanic and continental lithosphere.

Which of the following is in a place where continental rifting is occurring today?

Mt. Kilimanjaro in East Africa

Geologists from which continent were initially the least receptive to the continental drift hypothesis?

North America

In which direction is the Pacific Plate moving as the Hawaiian Islands are forming?

Northwest

Where would you expect to see deep ocean trenches?

Oceanic-oceanic convergent boundaries

Which of the following plates is getting significantly smaller?

Pacific

The largest lithospheric plate is the ________.

Pacific Plate

Why are volcanic chains associated with convergent boundaries?

Partial melting occurs due to subduction.

Why are oceanic ridges more elevated than the rest of the sea floor?

Ridges are elevated because the rocks are hot.

Which fault in Southern California was created by the sliding of the Pacific Plate past the North American Plate?

San Andreas Fault

Before the 1960s, how did geologists view the ocean basins and continents of the Earth?

Scientists believed that all ocean basins and landmasses were permanently fixed in their positions.

Which two plates are growing in size, and which plate is shrinking in size?

The African plate and the Antarctic plate are growing in size, whereas the Pacific Plate is shrinking in size

Which modern ocean basin started forming through the separation of two continents when Pangaea began to break up?

The Atlantic, by the separation of North America from Africa

Which of the following describes the movement of the North American and Caribbean Plates?

The Caribbean Plate is moving to the east and the North American Plate is moving to the west.

Which parts of Pangaea broke apart first?

The United States and Africa

What evidence first indicated to scientists that the continents were once connected?

The apparent jigsaw-like fit of continents together, as in the case of South America and Africa

Part complete Why does oceanic lithosphere subduct under continental lithosphere, whereas continental lithosphere does not subduct under oceanic lithosphere?

The oceanic lithosphere is thinner and denser than the continental lithosphere, which is thicker and less dense.

At a subduction zone where oceanic lithosphere meets continental lithosphere, which would subduct and why?

The oceanic lithosphere would subduct because it has a higher density at 3.0 grams per cubic centimeter.

How old are the oldest sediments that have been recovered by deep-sea drilling? Are they younger or older than the oldest continental rocks?

The oldest ocean sediments are 180 million years old and are far younger than the oldest continental rocks on Earth

What is the average rate of seafloor spreading occurring in the Atlantic Ocean and in the Pacific Ocean at the East Pacific Rise?

The rate of seafloor spreading at the Mid-Atlantic Ridge is 2 centimeters per year, whereas the rate of seafloor spreading at the East Pacific Rise is 15 centimeters per year.

Which two geologic processes result from vertical circulation within the mantle?

The upwelling of hot rock along oceanic ridges is the result of the mantle's upward circulation, whereas the subduction of oceanic plates at trenches is the result of the mantle's downward circulation.

Which of the following statements about the movement of the Indian Plate and the Eurasian Plate along the transect is correct?

They are converging at 48 mm/yr today, and they were converging at a rate of 59 mm/yr 60-70 m.y.a.

What is the relationship between continent edges and plate boundaries?

Very few plate boundaries follow the edges of continents.

The Himalayas formed as a result of ________.

a continent-continent convergence

A transform boundary is characterized by ________.

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

What was the Tethys Sea?

a piece of the Panthalassa Ocean that existed after the Pangaean supercontinent formed

What was Pangaea?

a supercontinent that began to break apart about 200 million years ago

The San Andreas Fault zone in California is an example of ________.

a transform plate boundary

A major problem with Wegener's Continental Drift Hypothesis was that he could not find ________ to explain his theory.

a viable mechanism

With regard 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, whereas areas in South America, Africa, India, Australia, and Antarctica were glaciated around the South Pole

The Himalayan Mountains are the tectonic product of a ________ between ________ and Eurasia that began 50 million years ago and still continues.

collision; India

Alfred Wegener developed the theory of ________.

continental drift

What kind of boundary is offshore?

convergent

What type of plate boundary is the oldest crust on Earth near?

convergent

Which type of tectonic boundary is the result of two tectonic plates colliding with each other?

convergent

Part complete Compared to the Earth's asthenosphere, the Earth's lithosphere is _______________________.

cooler and more rigid

Material that was once considered to be asthenosphere can change to lithosphere by ________.

cooling so that it will break

Name the correct order of rifting events.

crustal upwarp, rift valley, linear sea, ocean

An identifying characteristic of convergent boundaries is ________.

deep, linear trenches in the seafloor

The greater the ________, the ________-the angle of descent for the subducting slab.

density; steeper

When two plates move together, lithosphere is ________.

destroyed

The timing of __________ and continental breakup strongly correlate.

flood basalt formation

The lithosphere is the outer layer of the earth characterized by ________

hard rocks that break

Wegener's work is a good demonstration of the scientific method because ________.

his hypothesis did not pass all of the scientific tests to become a theory

Which of the following is not a type of plate boundary?

hot spot

The Hawaiian Island-Emperor Seamount chain formed as a result of ________.

hot spot activities

New York and London are on two separate plates so the distance between the cities is ________.

increasing

Some ________-rich minerals will align themselves with the existing magnetic field when they ________ from a magma

iron; cool

Iceland is a good example of a(n) ________.

island arc

All of Earth's ocean basins are ________.

less than 200 million years old

The Gulf of Aden represents which part of the rifting sequence?

linear sea

Plate tectonic boundaries were first identified by ________.

mapping earthquakes and volcanoes

Lithosphere is ________ at transform plate boundaries.

neither generated nor destroyed

The ________ is an example of an active, continent-continent collision.

northward movement of India into Eurasia

Japan and the Aleutian Islands have formed from a(n) ________ to ________ convergent boundary.

ocean; ocean

Oceanic lithosphere subducts (sinks into the asthenosphere) because ________.

old oceanic lithosphere is more dense that the asthenosphere

Which of the plates listed is the largest plate on the Earth?

pacific plate

The former late Paleozoic supercontinent is known as ________.

pangaea

What feature connects the South American Paraná and African Entedeka flood basalts?

seamount chain

Deep ocean trenches are surficial evidence for ________

sinking of oceanic lithosphere into the mantle at a subduction zone

The asthenosphere is the second layer of Earth characterized by ________.

soft rocks that flow easily

Which of the following features is considered a destructive plate margin?

subduction zone

Which of the following plate boundaries is moving the fastest?

the Pacific Plate at Samoa and Tonga

Which of the following major discoveries was not made near or after World War II?

the apparent "fit" of the coastlines of Africa and South Africa

What caused the formation of the Himalayas?

the collision of India with Asia

Evidence that tensile stresses are actively pulling the lithosphere apart in an ocean ridge system is given by ________.

the existence of a rift valley in a ridge system

Most deformation occurs along plate boundaries because ________.

the plates are in constant motion and as a result the boundaries are where they interact

When two continents converge, ________.

the sediments trapped between them are pushed up and deformed to make a mountain range

What was Panthalassa?

the single ocean that existed after the Pangaean supercontinent formed

At a location of plate convergence, a deep-ocean trench will form instead of a shallow ocean trench because _______________________

the subducting oceanic plate at a deep-ocean trench is older, cooler, and denser than a subducting plate at a shallow trench

In Wegener's time, scientists thought that the occurrence of fossils of the same organism in two different, disconnected continents was proof that ________.

there had once been land bridges separating the continents

Transform faults are different from convergent and divergent plate boundaries because _______________.

there is neither the creation nor the destruction of lithosphere at a transform fault, and plate movement is parallel to the length of a transform fault.

Wegener thought that ________.

there was once one big continent that later broke into several pieces

The San Andreas fault in California is a good example of a(n) ________ plate boundary.

transform

Which type of tectonic boundary is the result of two tectonic plates sliding past each other?

transform

At divergent plate boundaries, _________________

two plates move away from each other

The most obvious evidence of a plate boundary where two plates move apart is(are) ________.

upwelling of hot material from the mantle

The change from thinking the continents are stationary to understanding that the outer layer of the earth moves slowly nearly all of the time occurred primarily because ________.

we began to make global observations that required recognition that the continents and oceans had not always been in their current positions

As the South Atlantic basin ________ by seafloor spreading, Africa and South America are moving ________.

widens; further apart

Oceanic ridges are ________-than most mountain belts.

wider

Mount St. Helens and the other Cascade volcanoes are ________.

young, active stratovolcanoes built on a continental margin above a sinking slab of oceanic lithosphere

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

zone in the upper mantle that deforms by plastic flowage