Deck 4: Igneous Rocks and Plutons

Question 1

What phenomena does Bowen's Reaction Series help explain?

Answer 1

Bowen's Reaction Series explains how felsic magmas and rocks can come from mafic magmas,the order of mineral formation in a cooling magma,how the mineral composition of a magma changes with magma temperature,how magmas become enriched in Si,Al,and K,and the mineral associations that are common in igneous rocks.

Question 2

What is a mantle plume,and what causes one to erupt?

Answer 2

A mantle plume is a cylindrical plume of hot rock that rises through the mantle,most likely from the core-mantle boundary.As the rock rises,the pressure on it declines and the melting temperature of the rock decreases.Melting begins and creates magma.

Question 3

Briefly explain why Bowen's reaction series predicts that mafic intrusive rocks should be much more common than felsic intrusive rocks.

Answer 3

If crystal settling produces the magma,there would need to be about ten times as much mafic magma present to yield the amount of felsic rock.

Question 4

When looking at a hand sample of an igneous rock,how would you tell if it is plutonic or volcanic?

Question 5

What are the "scratches" on Devil's Tower,Wyoming?

Question 6

What is the average geothermal gradient for Earth?

Question 7

Give one reason why rhyolite flows are less common than basalt flows.

Question 8

Briefly explain how it is possible for a single magma to yield rocks of felsic,intermediate,and mafic composition.

Question 9

List three processes by which felsic and intermediate igneous rocks can be formed from more mafic magmas.

Question 10

Name some common uses of granitic rocks.

Question 11

Why can an intruding mafic magma assimilate felsic country rock,but an intruding felsic magma cannot assimilate mafic country rock?

Question 12

Briefly explain batholith formation.

Question 13

What does a phaneritic texture tell us about the history of an igneous rock?

Question 14

What is a pluton?

Question 15

Is the process of partial melting more likely to produce magmas which are more mafic or more felsic? Why?

Question 16

How did Shiprock,New Mexico form?

Question 17

How does lava differ from magma?

Question 18

What two types of volcanic features result from volcanism above a mantle plume? How are hot spots related to plate boundaries?

Question 19

What are flood basalts?

Question 20

Why does lava retain heat so well?

Question 21

The only minerals in the continuous branch of Bowen's reaction series are the ____________________.

Question 22

What role does stoping play in the emplacement of batholiths?

Question 23

Trapped gases in cooling lava form cavities called ____________________.Cinder cones may contain large amounts of ____________________ which contains more of these cavities than it does rock.

Question 24

Explain how batholiths and stocks formed via plate tectonics.

Question 25

Rapid cooling of magma results in a(n)____________________ grained texture called ____________________.

Question 26

Briefly explain how pegmatites form.

Question 27

Why do pegmatite mineral crystals grow so large?

Question 28

____________________ is the first ferromagnesian mineral to crystallize from a mafic magma.

Question 29

What does a glassy texture tell us about the history of an igneous rock?

Question 30

An igneous rock in which large mineral grains called ____________________ are suspended in a finely crystalline groundmass is called a(n)____________________.

Question 31

The two main categories of igneous rocks are ____________________ and ____________________.

Question 32

The increase in Earth's temperature with depth is called the ____________________.

Question 33

An example of a glassy igneous rock is ____________________.

Question 34

Partial melting of basalt,together with the processes of assimilation,____________________settling,and ____________________ mixing are believed to explain the generation of felsic intrusive magmas from ____________________ magmas.

Question 35

How do the holes form in vesicular igneous rocks,such as scoria and pumice?

Question 36

Igneous rocks having a phaneritic texture have ____________________ grains that ____________________ be seen easily by the naked eye.

Question 37

Explain how a laccolith is similar to a sill.

Question 38

How does a batholith differ from a stock?

Question 39

According to Bowen's reaction series,crystal settling should result in the magma being separated in lower layers rich in the early-formed ____________________ minerals,and upper layers enriched in later-formed ____________________ minerals.

Question 40

Basalt and gabbro are compositional equivalents,which means that they are made up of the same ____________________ but have different ____________________.

Question 41

____________________ are concordant,mushroom-shaped plutons.

Question 42

Intrusive igneous (plutonic)rocks ____.

A) solidify below the surface of the ground
B) solidify above the surface of the ground
C) form by crystallization of magmas intruded into surrounding rocks
D) solidify below the surface AND form by crystallization of intruded magmas
E) solidify above the surface AND form by crystallization of intruded magmas

Question 43

The ultramafic rock composed predominantly of ____________________ is known as peridotite and is likely the rock that makes up the part of Earth known as the ____________________.

Question 44

When magma cools slowly,crystal growth proceeds at a relatively ____________________ speed,and the resultant rock is ____________________ in texture.

Question 45

Although all compositions are represented,most plutons are ____.

A) felsic rocks
B) intermediate rocks
C) mafic rocks
D) felsic and mafic rocks
E) none of these

Question 46

Igneous rocks with a two-stage intrusive-extrusive origin are recognized by a texture which is ____.

A) aphanitic
B) porphyritic
C) glassy
D) phaneritic
E) pyroclastic

Question 47

The most widely accepted explanation for chains of volcanoes in the oceans and lines of volcanoes on land is that they formed at ____.

A) divergent plate boundaries
B) normal faults
C) hot spots
D) convergent plate boundaries
E) transform faults

Question 48

The largest intrusive bodies are called ____________________ and by definition,they must have at least ______ square kilometers of surface area.

Question 49

Most igneous rocks are classified by what?

A) texture
B) composition
C) size
D) texture and composition
E) size and composition

Question 50

Rhyolite and granite are extrusive and intrusive rocks formed by volcanism and ____________________,which form at or near plate boundaries as the result of ____________________ and/or ____________________ of plates.

Question 51

The process of assimilation ____.

A) includes melting and incorporation of inclusions
B) includes the inclusion of country rock in an intrusive magma
C) can explain some of the felsic mineral enrichment of a mafic magma
D) results in the cooling of a magma body
E) all of these

Question 52

Concordant tabular sheetlike plutons are called ____________________,whereas discordant tabular plutons are called ____________________.

Question 53

The Columbia Plateau basalts issued from fissures which are now preserved as ____________________.

Question 54

A dark colored igneous rock with no visible crystals cooled ____.

A) slowly in a magma chamber
B) quickly in a magma chamber
C) slowly on the Earth's surface
D) quickly on the Earth's surface
E) none of these

Question 55

Aphanitic,phaneritic,and porphyritic are textural terms that ____.

A) refer to fine-grained, course-grained, and mixed grained crystal sizes, respectively.
B) refer to formation by slow cooling, fast cooling, and mixed cooling rates, respectively.
C) are indicative of volcanic, plutonic, and mixed plutonic-volcanic origins, respectively.
D) are fine-grained, coarse grained, and mixed-grained crystal sizes respectively and are indicative of volcanic, plutonic and mixed plutonic-volcanic origins respectively
E) all of these

Question 56

Large crystals found in a fine-grained groundmass can indicate what?

A) origin from a magma with an early intrusive phase followed by an extrusive phase
B) origin from a magma with an early extrusive phase followed by an intrusive phase
C) a rock of mixed volcanic-plutonic origin
D) intrusive slow cooling
E) origin from a magma with an early intrusive phase followed by an extrusive phase; a rock of mixed volcanic-plutonic origin

Question 57

Batholiths and stocks can be important sources of minerals such as ____________________ and ____________________.

Question 58

Andesite and ____________________ are respectively,____trusive and ____trusive rocks formed in volcanic chains along ____________________ plate boundaries.

Question 59

Most plutons form ____.

A) well within plates
B) at plate boundaries
C) without regard to plate boundaries
D) above the land surface
E) all of these

Question 60

Where are mantle plumes primarily found?

A) divergent plate boundaries
B) convergent plate boundaries
C) transform plate boundaries
D) not at plate boundaries
E) none of these

Question 61

Bowen's Reaction Series explains the order of mineral formation with decreasing temperature.

Question 62

Any individual volcano always erupts magmas of the same type.

Question 63

Granite and rhyolite are extrusive and intrusive igneous rocks of the same composition.

Question 64

The process of assimilation includes the incorporation of felsic country rock.

Question 65

Natural glass such as obsidian forms when magma does what?

A) cools too rapidly for crystals to form
B) cools rapidly and very tiny crystals form
C) cools too slowly for crystals to form
D) doesn't cool
E) none of these

Question 66

Batholiths are emplaced by forceful injection as magma moves upward through country rock.

Question 67

Pegmatites are rocks of felsic composition that are similar to granite.

Question 68

Laccoliths are sills that inflate,causing the overlying rock to bow upward.

Question 69

What is a vesicular felsic rock called?

A) pumice
B) scoria
C) obsidian
D) tuff
E) volcanic breccia

Question 70

The process of assimilation partly explains why felsic intrusive rocks are much more common than mafic intrusive rocks.

Question 71

Igneous rocks with a texture that is so fine-grained that the crystals are too small to see is ____.

A) aphanitic
B) porphyritic
C) glassy
D) phaneritic
E) pyroclastic

Question 72

Igneous rocks formed by explosive volcanic activity have a texture that is termed what?

A) aphanitic
B) porphyritic
C) glassy
D) phaneritic
E) pyroclastic

Question 73

Geologists agree that hot-spot volcanism results from a rising mantle plume.

Question 74

Bowen's Reaction Series explains why Si-rich minerals are the last to crystallize from a magma.