GEOL 101

This diagram shows a convergent plate boundary. Which of the following statements is true? qs 8 hw 1

This is an example of ocean-continent convergence; the plate on the right is being subducted.

Order the steps that lead to assimilation.

1. a magma forms and begins to migrate through the crust 2. blocks of the surrounding silica-rich crust break off and become incorporated into the magma 3. Incorporated crustal blocks within the magma melt, mixing with the magma. 4. The amount of silica in the magma increases and the magma composition changes accordingly

Which of the following statements is FALSE? Mafic minerals

form rhyolite and granite.

Earth's core

generates Earth's magnetic field.

Alfred Wegener's idea of continental drift was rejected by American geologists because

he could not conceive of a valid mechanism that would cause continents to shift positions.

Identify the factors that cause melting and thus the formation of magma.

heat transfer addition of volatiles decompression

A moving, glowing cloud of hot gases and volcanic pieces

is called a pyroclastic flow or nuée ardente.

Which of the following statements is FALSE? Felsic (or silicic) magma

is less viscous than mafic magma.

Identify the FALSE statement. Continental crust

is thinner than ocean crust.

One type of volcanic hazard buries crops, spreads toxic chemicals, and destroys moving parts in machinery . This type of hazard is

pyroclastic ash.

Which of the following is a mineral?

salt (NaCl)

Which plate boundary is associated with transform boundary

shear stress

Sort outcomes of ocean-ocean (oceanic) convergence.

subduction volcanism

"Wet" igneous rock melts at a lower temperature than the "dry" version of that same rock because

the addition of volatiles in "wet" rocks lowers their melting temperature.

The global occurrence of earthquakes reveals that

they usually occur on the boundaries of plates or at hot spots.

Which of the following is NOT an intrusive igneous structure?

pillow lava

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

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

Identify the FALSE statement. Lava of low viscosity

. is most often a "cool" temperature lava.

Which of Earth's layers accounts for most of the volume of Earth?

the mantle

Which of the following was NOT a line of evidence used by Wegener to develop this theory that continents drift?

the presence of earthquakes in seismic belts along trenches, ridges, and fracture zones

Radiometric dating of a magnetic anomaly stripe of rock that is 225 km away from the mid-ocean ridge axis gives an age of 4.5 million years. Assuming a constant rate, seafloor spreading in this area occurs at a rate of

. 5 cm per year.

Order the steps involved in fractional crystallization.

1. Magma, after entering through the bottom of the magma chamber, reaches the top of the chamber where temperatures are lower. 2.Magnesium- and iron-rich minerals begin to crystallize 3. Mineral crystals, having a higher density than liquid magma, sink to the bottom of the magma chamber. 4. The magma shifts toward a more intermediate composition

Outline the progression of hot spot related seamount formation.

1. a volcanic forms over a hot spot 2. the volcano is carried away from the hot spot source by the movement of the tectonic plate, causing it to go extinct. 3. as the island ages it cools and subsides 4. the island is eroded until it is no longer emergent and becomes an underwater seamount

Order the steps in supercontinent formation and breakup.

1. subduction consumes an ocean basin 2. continents collide and form a supercontinent 3. rifting takes place 4. seafloor spreading produces new lithosphere, and continents move apart.

Order the steps that lead to seafloor spreading.

1. the asthenosphere beneath diverging plates rises and melts 2. a magma chamber forms beneath the ridge axis 3. Magma rises to the surface and erupts via submarine volcanoes 4. newly formed crust is moved laterally away from the ridge

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

Rank the following steps describing how a clastic sedimentary rock forms from its pre-existing parent rock

1. weathering 2. erosion 3. transportation 4.deposition 5.lithification

Plate tectonics theory was widely accepted by scientists in what decade?

1960s

Over 20 million years, the total offset across the fault is 480 kilometers. What is the average rate of motion along the fault?

2.4 cm per year

The chain of Hawaiian Islands extends northwest across the Pacific as shown in the figure. The island of Hawaii is the youngest, and the islands get progressively older to the northwest. How does plate tectonic theory explain this?

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

How is a lahar different from a pyroclastic flow?

A pyroclastic flow is a mixture of debris and air, whereas a lahar is a fast, liquid flow.

Contrast continental collision and volcanic island arc formation.

Continental collision: involves continental crust Volcanic island arc: involves volcanism, involves oceanic crust, involves subduction

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.

Order the steps of continental volcanic arc formation.

Convergence begins 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, rides through the continental lithosphere. 4. Lava erupts onto the surface, forming volcanoes.

Order the steps of volcanic island arc formation.

Convergence begins 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.

Which plate boundary is associated with divergent boundary

Crustal thinning

Which of the following statements are true about partial melting?

Felsic components of the parent rock tend to go into the liquid state first during partial melting. Partial melting results in magmas that are more felsic in composition than the parent rock. As more of the rock melts during partial melting, the magma becomes more mafic than the original melt that formed.

How does subduction trigger melting?

Flux melting of the asthenosphere above the subducting slab creates a rising melt.

Granite

Is felsic in composition

Which of the following is NOT a characteristic of a rock?

It has a definable chemical composition.

Why does magma rise from depth to the surface of the Earth?

It is less dense than the rocks that surround it. The surrounding rock creates pressure that pushes it upward.

Select statements true of the Hawaiian Hot Spot.

It produced the Hawaiian Islands. It produced the Emperor Seamounts.

What does grain size generally indicate about the cooling of a melt?

Larger crystals indicate the melt cooled gradually.

Which statements are true about lava?

Lava is molten rock that has been erupted onto the surface of the Earth. Lava composition can vary greatly among different types of volcanoes

What composition of magma is produced by melting at lower temperatures? At higher temperatures?

Lower temperatures: 1. felsic 2. intermediate 3. mafic 4. ultra mafic Higher temperatures

The boundary separating the crust from the mantle is called the

Moho

Mt. St. Helens erupted explosively in 1980. Geologists find evidence of many eruptions of Mt. St. Helens, dating back 37,000 years. The mountain is huge and is composed of layers of lava and pyroclastics. Which of the following is therefore most likely TRUE?

Mt. St. Helens is a stratovolcano (or composite volcano).

The apparent tendency of the north (or south) magnetic pole to vary in position over time is termed

Polar wander

Identify statements true of Pangaea.

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

Why are there so many different types of magma?

The source rock from which magmas form may differ. Different magmas may mix to form a new magma

Which of the following does NOT describe a structural feature of a volcano?

Vesicle

A mineral, as geologists understand the term, is a naturally occurring solid substance with a definable chemical composition and

a fixed crystalline structure.

The presence of pillow lava is evidence of what volcanic circumstance?

a submarine volcano

a lahar is

a volcanic mud flow that resembles fluid concrete

Bowen's reaction series

allows a geologist to predict what minerals will be found in a given igneous rock.

Seafloor spreading is driven by volcanic activity that occurs

along mid-ocean ridges.

The chain of volcanoes along the west coast of South America (the Andes Mountains) exists because

an oceanic plate is subducting under the western edge of the South American Plate.

Which plate boundary is associated with convergent boundary

andesitic volcanism crustal thickening

Which of the following statements is FALSE? Igneous rocks

are coarse-grained if they cool extrusively.

Pillow basalts

are formed in a submarine environment.

A black, fine-grained tabular intrusion between two layers of horizontal sedimentary rock must logically be a

basaltic sill.

Alfred Wegener proposed the idea of continental drift after he observed evidence from fossils, glacial deposits, and the fit of the continents that suggested all of the continents were once

combined to form a supercontinent (which he termed Pangaea) in the late Paleozoic through the Mesozoic.

Which is NOT a tectonic setting for igneous activity?

continental transform fault zones

The distinctive vertical joints seen in this basalt flow most likely formed as a consequence of which of the following?

contraction into hexagonal forms during the final stage of cooling

The Moho is the boundary between Earth's

crust and mantle

Sort outcomes of continental collision

crustal thickening mountain building

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.

Choose the most likely product of partially melting a rock of intermediate composition.

felsic magma

The image shows Mount St. Helens two years after its 1980 eruption. Given the shape of the volcano and presence of a lava dome (source of the steam), what is the most likely composition of the associated magma? (HW 4 qs 4)

felsic to intermediate

Earth's magnetic field is created by

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

Marine magnetic anomalies result from seafloor spreading in conjunction with

magnetic polarity reversals.

Which of the following are methods used by geologists to predict a volcanic eruption?

measuring an increased incidence of earthquakes observing changes in the shape of a volcano measuring an increased occurrence of gaseous emissions measuring an increase in heat flow

Lava is

molten rock that cools and hardens on earth's surface

The center of a mid-ocean ridge is where

new oceanic lithosphere is being created.

Which of the following statements is FALSE? Volcanic arcs

occur at divergent plate boundaries.

The San Andreas fault is

one of the few transform faults that cut across continental lithosphere.