Geology Chapter 2A

Which of the following statements about lithosphere and asthenosphere is true?

Lithosphere consists of the crust and the upper mantle and behaves like a rigid layer that breaks or bends rather than flowing like the asthenosphere.

The rate of plate motion

can be expressed as relative plate velocity, which describes movement of one plate in relation to another plate.

This diagram shows how the tilt of a magnetic needle changes with latitude. Which component of the Earth's magnetic field does this tilt represent?

inclination

Oceanic crust

is covered by a thin blanket of sediment that thickens away from the ridge axis.

Magnetic anomalies are

places where the magnetic field strength is either greater or less than the expected strength.

A global map of seismicity shows seismic trends indicating the location of

plate boundaries.

According to current plate tectonics theory,

plates are composed of the crust and the uppermost part of the mantle.

During World War II, the military imaged the seafloor by sending pulses of sound waves down through the water and measuring the time it took for the sound to bounce off the seafloor and return to the receiver. This method is called

sonar

Accretionary prisms form due to what process?

subduction

Oceanic lithosphere

that is 10 million years old is cool enough to be denser than the asthenosphere, so it can sink down into or through the asthenosphere.

Order the steps that lead to seafloor spreading.

the asthenosphere beneath diverging plates rises and melts a magma chamber forms beneath the ridge axis Magma rises to the surface and erupts via submarine volcanoes newly formed crust is moved laterally away from the ridge

The Earth's magnetic field is created by

the flow of liquid iron in the Earth's molten outer core.

The global occurrence of earthquakes reveals that

they occur on the boundaries of plates or at hotspots

Order the steps in continental rift formation.

1) The lithospheric mantle begins to stretch horizontally and thin vertically. 2) The crust fractures, and faults develop. 3) Large fault blocks of crust slide down into the widening rift. 4) Magma erupts as lava, creating volcanoes along and near the center of the rift.

Order the steps of volcanic island arc formation.

1. a subduction trench forms where the subducting plate bends downward into the mantle 2. an accretionary prism begins to form 3. magma, created by flux melting of the mantle, rises through the overriding plate. 4. Lava erupts onto the surface, forming volcanoes.

Order the steps of continental volcanic arc formation.

1. a subduction trench forms where the subducting plate bends downward into the mantle2. an accretionary prism begins to form3. Magma, created by flux melting of the mantle, rides through the continental lithosphere.4. Lava erupts onto the surface, forming volcanoes.

Modern plate tectonic theory was developed in what decade?

1960s

The chain of the Hawaiian Islands can be used to calculate the rate of movement of the Pacific Plate over the last few million years. The island of Hawaii currently sits on the hot spot, and is therefore 0 million years old. The island of Kauai used to sit on the hot spot; it is approximately 5.1 million years old and is now approximately 473 km away from the hot spot, to the northwest. Given these parameters, what is the average rate of motion of the Pacific Plate in centimeters per year? (Remember to convert your units properly!)

9 cm per year

As the map below shows, the oldest seafloor is generally less than 200 million years old. Why?

All oceanic lithosphere eventually gets subducted beneath the continents by the time it is 200 million years old.

Identify the true statement associated with this diagram.

Apparent polar-wander paths for different continents do not match, so each continent must be moving independently of the others.

Identify statements true of Pangaea.

Pangaea was one of several supercontinents that have formed and broken up during Earth's history. Rates of seafloor spreading in the Atlantic Ocean are compatible with what is known about the breakup of Pangaea. The regional-scale folds visible in the Appalachian Mountains are remnants of Pangaea's formation.

Identify the true statement.

Plates shift the continents around as they move, so Earth's surface is constantly changing.

Identify the true statement.

Positive magnetic anomalies occur where seafloor basalt has the same polarity as Earth's present-day magnetic field.

Identify the true statement.

Some magma generated during seafloor spreading erupts from submarine volcanoes to form basalt.

Of the choices below, select the one that accurately pairs the feature with the type of plate boundary at which it occurs.

Trenches occur at subduction zones.

The Himalayas are growing because

a continental plate is colliding with another continental plate there.

The island of Hawaii is the youngest, and the islands get progressively older to the northwest. Plate tectonic theory explains this as

a hot spot currently sitting under Hawaii and the Pacific Plate moving across it in a northwesterly direction.

Seafloor spreading is driven by volcanic activity that occurs

along mid-ocean ridges.

Wegener's theory of continental drift took decades to be accepted

because Wegener couldn't explain how continents moved.

Sort outcomes of continental collision versus those related to ocean-ocean (oceanic) convergence.

continental collision: - crustal thickening - mountain building oceanic convergence: - subduction - volcanism

According to the theory of plate tectonics, the plates are:

discrete pieces of lithosphere which move with respect to one another moved by the creation of new crust and subduction of old crust

Which of the following variables could influence the width of marine magnetic anomalies on the floor of the ocean?

duration of the magnetic polarity event rate at which the plates are moving away from the mid-ocean ridge

Plate movement is influenced by each of the following EXCEPT

mantle plumes, which are created when hot rock rises up from the deep mantle and creates melting at the base of the lithosphere.

The center of a mid-ocean ridge is where

new oceanic lithosphere is being created

Sort the following processes those likely to be related to a transform boundary or those likely associated with other boundary types.

transform boundary: - earthquakes other boundary: - divergence - convergence - subduction

Sometimes more than two plates come together at a special kind of plate boundary, as shown in the figure. What type of plate boundary feature is shown here at the intersection of the African, Indian, and Antarctic plates?

triple junction