Deck 4: Magma, Igneous Rocks, and Intrusive Activity

Question 1

What is the geologic definition of texture?

A)How the sample feels to the touch
B)The mineral content of the sample
C)The percentage of silica in a sample
D)Size, shape, and arrangement of mineral grains in the sample

Answer 1

D

Question 2

Which of these textures help geologists determine if a rock is of intrusive origin?

A)Aphanitic
B)Pyroclastic
C)Porphyritic
D)Phaneritic

Answer 2

D

Question 3

Which of the following substances is not a volatile found in magma?

A)O₂
B)CO₂
C)H₂O
D)SO₂

Answer 3

A

Question 4

What three components make up most magmas?

A)Silicon, potassium feldspar, and muscovite
B)Water, melted rock, and solid crystals
C)Lava, ash, and gas
D)Liquid portion, solid portion, gaseous portion

Question 5

What is the term used to describe increased temperature with depth in the Earth?

A)Decompression melting
B)Convection cells
C)Geothermal gradient
D)Hydrothermal alteration

Question 6

Which of the following minerals is not a ferromagnesian mineral?

A)Olivine
B)Potassium feldspar
C)Pyroxene
D)Biotite mica

Question 7

Which of these textures help geologists determine if a rock is volcanic in origin?

A)Pegmatitic
B)Aphanitic
C)Porphyritic
D)Phaneritic

Question 8

Which two minerals define a felsic composition?

A)Pyroxene and amphibole
B)Muscovite and biotite micas
C)Quartz and potassium feldspar
D)Plagioclase feldspar and biotite mica

Question 9

Which of the following statements best describes the relationship between pressure and melting point in the Earth's Interior?

A)Higher pressure leads to lower melting points.
B)Melting points of rocks are not dependent on changes in pressure.
C)Higher melting points are determined by higher pressures.

Question 10

Which igneous texture has visible crystals that are a few millimeters across?

A)Phaneritic
B)Aphanitic
C)Pegmatitic
D)Porphyritic

Question 11

What is a volatile?

A)A hostile person
B)Solid mineral crystals in a melt
C)Gases dissolved in a magma
D)The liquid portion of a magma

Question 12

What substance makes ion migration easier in the later stages of magma crystallization, which allows abnormally large mineral crystals to form and create pegmatites?

A)Water
B)Oxygen
C)Silica
D)Iron

Question 13

________ is a felsic igneous rock with a meringuelike vesicular texture, consisting of very small holes, created by small shards of volcanic glass.

A)Scoria
B)Obsidian
C)Granite
D)Pumice

Question 14

Peridotite is the main constituent of which part of the Earth?

A)Crust
B)Magma chambers
C)Rift zones
D)Upper mantle

Question 15

What creates the small holes found in a vesicular texture?

A)Liquid water
B)Volatiles
C)Soluble minerals
D)Weathering

Question 16

What was the rate of cooling and the environment of formation for an extrusive igneous rock and why?

A)Slow because the magma was insulated below the surface
B)Fast because it was erupted from a volcano
C)Slow because it cooled in a volcanic lava flow far from the vent
D)Fast because it cooled 6 kilometers below the surface

Question 17

________ is molten rock that is below the Earth's surface and retains most of its volcanic gases.

A)Lava
B)Pumice
C)Magma
D)Volatiles

Question 18

Which mineral group makes up most igneous rocks?

A)Carbonates
B)Sulfides
C)Silicates
D)Halides

Question 19

Select the choice below that best describes the role of volatiles in an ascending magma.

A)Volatiles increase the rate of crystallization in intrusive structures.
B)Volatiles will force the magma to contract as it rises.
C)Volatiles will shatter surrounding rocks, making it easier for the magma to rise.
D)Volatiles will expand with decreasing pressure, then melt upward.

Question 20

What role does water play in generating magma?

A)Water lubricates the path for subducting plates, allowing them to subduct deeper.
B)Water lowers the density of the rock, allowing it to melt.
C)Water cools the rock, preventing melting.
D)Water lowers the melting temperature of the rock, allowing it to melt.

Question 21

What magma forms from the partial melting of mantle material?

A)Ultramafic magma
B)Magmatic differentiation
C)Silicic magma
D)Secondary magma

Question 22

Where do ultramafic rocks form?

A)At convergent boundaries
B)In volcanoes
C)At the Earth's surface
D)At the upper mantle

Question 23

A ________ texture includes coarse phenocrysts surrounded by a phaneritic groundmass.

A)pegmatitic
B)porphyritic
C)glassy
D)aphanitic

Question 24

The granitic igneous rocks that make up the Sierra Nevada Mountains in California and Nevada are ________.

A)extrusive
B)intrusive
C)metamorphic

Question 25

Which of the following statements best describes the formation of secondary magmas?

A)Decompression melting creates a mafic magma from mantle material.
B)Iron-rich minerals will form in a cooling magma and leave the remaining melt with a more silicic composition.
C)Partial melting of felsic rocks creates a silica-rich magma.
D)Water dehydrating from a subducted plate will melt mantle material.

Question 26

________ describes how an entire suite of silicate minerals can form from a single basaltic magma as it cools and crystallizes.

A)The theory of plate tectonics
B)Moh's hardness scale
C)Bowen's reaction series
D)The geologic rock cycle

Question 27

When magma forms, it rises up through the crust.Why does magma rise?

A)It is forced upward by pressure from the Earth's interior.
B)It is less dense.
C)It is uplifted by tectonism.
D)It is forced out by volcanism.

Question 28

Which process is thought to generate most felsic magmas?

A)Decompression melting in a continental rift zone
B)Crystal settling during magmatic differentiation
C)Heat from basaltic magma partially melting overlying crust
D)Friction along the crust in a convergent plate boundary

Question 29

What is the name of the preexisting rock through which intrusive igneous bodies intrude?

A)Acid rock
B)Parent rock
C)Stock
D)Country rock

Question 30

________ describes the formation of one or more secondary magmas from a single parent magma.

A)Magmatic differentiation
B)Hydrothermal alteration
C)Decompression melting
D)Partial melting

Question 31

________ will occur when continental collisions occur, thickening the crust and forcing some rocks to a depth where melting can take place.

A)Decompression melting
B)Rifting
C)Extension
D)Partial melting

Question 32

If an igneous rock is heated, which mineral will be the very last mineral left to melt according to the Bowen's reaction series?

A)Quartz
B)Pyroxene
C)Potassium feldspar
D)Olivine

Question 33

Will density increase or decrease with the crystallization of a magma?

A)Decrease
B)Increase

Question 34

Welded tuff consists of ash surrounding large, jagged, irregularly-shaped pieces of material.What is this material and where does it come from?

A)Mineral crystals that formed during cooling
B)Rock fragments that erupted from the volcano
C)Gas pockets from volatiles in the lava
D)Slivers of volcanic glass from the lava

Question 35

The partial melting of mafic rocks would produce what composition of magma?

A)Ultramafic
B)Mafic
C)Intermediate
D)Felsic

Question 36

A ________ is a mushroom-shaped pluton that forms by injecting magma between sedimentary strata, forcing the upper layers to arch upward.

A)dike
B)sill
C)batholith
D)laccolith

Question 37

________ has a large percentage of voids and is lightweight, so therefore has the ability to float in water.

A)Basalt
B)Pegmatite
C)Pumice
D)Scoria

Question 38

A ________ is a tabular, concordant pluton that is nearly horizontal and forms when magma exploits a weakness between sedimentary layers.

A)dike
B)sill
C)batholith
D)laccolith

Question 39

Which of the following best describes a pegmatitic texture?

A)Large crystals that form in a fluid-rich environment late in crystallization
B)Porous texture resulting from escaping volatiles
C)Fine-grained texture composed of microscopic crystals
D)Several large crystals surrounded by a fine-grained matrix

Question 40

If an igneous rock is heated, which mineral melts first according to Bowen's reaction series?

A)Quartz
B)Pyroxene
C)Potassium feldspar
D)Olivine

Question 41

Concordant plutons cut across existing structures while discordant plutons are parallel to existing features.

Question 42

Dikes tend to form as solitary structures.

Question 43

Mineral crystals that form early in the crystallization process will have better-developed crystal faces than later crystals.

Question 44

Refer to the scenario above.Assuming a temperature of 20°C at the ground surface, what is the temperature at a depth of 2 miles?

Question 45

How will mantle-derived magma change when it ponds against crustal rocks?

Question 46

Magmas in the magma chamber of a volcano are often compared to soda to explain how the magma is erupted.How is magma like a bottle of soda? What happens to both substances when the pressure changes?

Question 47

In the process of a magma cooling and crystallizing, if the original melt contained large amounts of iron, why isn't quartz a ferromagnesian mineral?

Question 48

What is the definition of magma mixing?

A)When magma mixes with fluids to become more dilute
B)When rising magma melts surrounding country rock and incorporates it
C)When one rising magma will overtake a second and the two intermix
D)When magma incorporates more dissolved gases

Question 49

Temperatures will decrease with increasing depth into the Earth.

Question 50

What is the role that depth can play on cooling and crystallization of igneous rocks?

Question 51

When teaching about igneous rocks, one trick instructors often implement to help students determine the igneous composition of the samples is to use the color of the rocks as a guide.Explain how the color of an igneous rock can often be used as an indicator of its igneous composition.Be sure to reference specific minerals for each composition.

Question 52

How could a researcher use magmatic differentiation to determine if a batholith is the result of one body of magma cooling and crystallizing or multiple bodies of magma?

Question 53

Peridotite that undergoes partial melting will create a melt enriched in ________.

A)iron, magnesium, feldspars, and silica
B)silica
C)iron and magnesium
D)feldspars and silica

Question 54

Plutonic bodies that have a surface exposure less than 100 km² are called ________.

A)dikes
B)stocks
C)swarms
D)batholiths

Question 55

Refer to the scenario above.How would you expect the geothermal gradient to change if this borehole were drilled near Yellowstone National Park? Why?

Question 56

Most sills are intrusive igneous structures that display a fine-grained texture.

Question 57

The two branches of Bowen's reaction series are the continuous series and the discontinuous series.In what ways do the minerals in the discontinuous series differ from each other? And the minerals in the continuous series?

Question 58

Refer to the scenario above.How does this gradient compare to the average geothermal gradient?

Question 59

Which of the following regions will primarily erupt silica-rich lavas?

A)Oceanic mantle plumes
B)Oceanic rift zones
C)Continental margins
D)Impact craters

Question 60

Igneous rocks with an andesitic composition are found along volcanic island arcs.

Question 61

What are two ways a primary magma can be generated?

Question 62

Of the following substances, which are the common elements in igneous rocks?
Silicon, rubidium, nitrogen, carbon, sodium, manganese, hydrogen, oxygen, potassium, calcium, phosphorous, aluminum, iron, chlorine, magnesium, uranium, helium, gold

Question 63

Magma can form up to 250 km deep in the Earth.If magma forms at such a depth, how can magma at that depth rise through the mantle and the crust toward the surface?

Question 64

At what temperature will peridotite melt along the geothermal gradient?

Question 65

Is the rock in the above image intrusive or extrusive?

Question 66

All rocks are classified according to ________ and ________.

Question 67

Explain the processes occurring in the figure above that are generating magma.At what kind of tectonic boundary are such processes common?

Question 68

Why would rhyolite deposits be less common than granite deposits?

Question 69

List the intrusive igneous textures below.
Phaneritic, aphanitic, glassy, pyroclastic, pegmatitic

Question 70

What would happen to the peridotite if there was a decrease in pressure from that at the depth of 100 km?

Question 71

How does magma differ from lava?

Question 72

Follow the geothermal gradient to the depth of 100 km.In which state of matter will peridotite exist at 100 km?

Question 73

Magma that forms batholiths forms in the mantle and must migrate upward.However, the sedimentary and metamorphic rocks that surround these batholiths are only moderately deformed.How does a rising magma body make its way through several kilometers of solid rock to be emplaced as a batholith? (Start your journey in the mantle.)

Question 74

Slow cooling produces ________ crystals, whereas fast cooling produces ________ crystals.

Question 75

How does the presence of silica affect the temperature and viscosity of magma?

Question 76

In July 1863, Union and Confederate forces fought in a three-day battle at Gettysburg, Pennsylvania.The Confederate position was on Seminary Ridge, an igneous dike.The Union position was on Cemetery Ridge, an igneous sill.Using what you know about the history of the battle, interpret how the geology of the battlefield aided the Union victory.