Deck 4: Igneous Rocks and Intrusive Igneous Activity

Question 1

What is viscosity? What is the effect of temperature and composition on the viscosity of magma? At the same temperature, which composition of magma will be the most viscous: felsic, intermediate, or mafic? Which will be the least viscous?

Answer 1

Viscosity is resistance to flow. Higher temperature fluids have less viscosity than lower temperature fluids. In magma, higher silica magmas are more viscous than magmas with less silica. So mafic magmas are the less viscous compared to felsic magmas.

Question 2

What are dikes, sills, and laccoliths?

Answer 2

Dikes and sills are tabular or sheet-like igneous intrusive bodies. Dikes are discordant (they cut across rock layers), and sills are concordant (they parallel the layering in rocks). Laccoliths are sills that inflate, causing the overlying rock to bow upward. A laccolith has a mushroom-like shape.

Question 3

What are the effects of magma mixing on magma composition?

Answer 3

Magmas of different composition coming into contact in the magma chamber will result in mixing of the magmas. The mixing process will result in a magma that is different in composition from the original composition of the magmas but with certain compositional similarities shared during mixing.

Question 4

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

Question 5

Briefly explain batholith formation.

Question 6

How are gabbro and basalt similar, and how are they different? How about diorite and andesite? Granite and rhyolite? How are basalt, andesite, and rhyolite the same and how are they different? How about gabbro, diorite, and granite?

Question 7

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

Question 8

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

Question 9

How does mafic magma originate from ultramafic rock at a spreading ridge?

Question 10

What are the three major types of magmas? How are they defined? What elements increase or decrease in the composition of the three types?

Question 11

What causes volcanism at a subduction zone, and how does Bowen's reaction series explain the composition of the magmas there?

Question 12

What are aphanitic and phaneritic textures, and what do they say about the way the rock formed?

Question 13

What phenomena does Bowen's reaction series help explain?

Question 14

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

Question 15

How do volcanic necks form?

Question 16

What are pegmatites, and how do they form?

Question 17

What causes the volcanism at spreading ridges?

Question 18

Briefly explain why felsic intrusive rocks are actually more common than mafic intrusive rocks.

Question 19

Why does Bowen's reaction series predict that mafic intrusive rocks should be much more common than felsic intrusive rocks?

Question 20

What are the effects of assimilation on magma composition?

Question 21

What does a mantle plume result in?

Question 22

What are flood basalts?

Question 23

How does lava differ from magma?

Question 24

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

Question 25

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

Question 26

What role does stoping play in the emplacement of batholiths?

Question 27

Why do pegmatite mineral crystals grow so large?

Question 28

What is viscosity?

Question 29

What is an igneous rock?

Question 30

How does a dike differ from a sill?

Question 31

How does a batholith differ from a stock?

Question 32

What does a phaneritic (coarse grained) texture tell us about the history of an igneous rock?

Question 33

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

Question 34

Explain how a laccolith is similar to a sill.

Question 35

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

Question 36

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

Question 37

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

Question 38

What two main parameters are used in the classification of igneous rocks?

Question 39

Why does lava retain heat so well?

Question 40

What is a pluton?

Question 41

The presence of country rock inclusions in an intrusive igneous rock is evidence that the rock underwent the process of ____________________.

Question 42

The presence of ____________________, which are incompletely melted pieces of rock within igneous rocks, demonstrates that ____________________ occurs.

Question 43

____________________ are concordant, mushroom-shaped plutons.

Question 44

An igneous rock in which large mineral grains called ____________________ are suspended in a finely crystalline groundmass is referred to as ____________________.

Question 45

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

Question 46

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

Question 47

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

Question 48

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

Question 49

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 50

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

Question 51

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

Question 52

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

Question 53

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

Question 54

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

Question 55

Completion
Igneous rocks of dark color are generally rich in the chemical elements ____________________ and ____________________, while those of light color are generally rich in ____________________ and ____________________.

Question 56

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

Question 57

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 58

According to the Bowen's reaction series ____________________ is the first ferromagnesian mineral to crystallize from a mafic magma.

Question 59

Batholiths are mostly emplaced by _________________ _________________ as magma moves upward into country rock.

Question 60

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

Question 61

Most igneous rocks are classified by:

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

Question 62

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 63

Mantle plumes are found primarily at:

A) divergent plate boundaries.
B) convergent plate boundaries.
C) transform plate boundaries.
D) intraplate regions.
E) none of the above

Question 64

Large crystals found in a fine-grained groundmass can indicate:

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) origin from a magma with an early intrusive phase followed by an extrusive phase AND a rock of mixed volcanic-plutonic origin.
E) origin from a magma with an early extrusive phase followed by an intrusive phase AND a rock of mixed volcanic-plutonic origin.

Question 65

Although all compositions are represented, most plutons are:

A) felsic rocks.
B) intermediate rocks.
C) mafic rocks.
D) felsic and mafic rocks.
E) felsic, intermediate, and mafic rocks.

Question 66

Igneous rocks with a two-stage intrusive-extrusive origin are recognized by a texture that is:

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

Question 67

Most plutons form:

A) well within plates.
B) at plate boundaries.
C) without regard to plate boundaries.
D) at plate boundaries or without regard to plate boundaries.
E) at, well within, or without regard to plate boundaries.

Question 68

The discontinuous branch of Bowen's reaction series includes various compositions of plagioclase, from calcium-rich to sodium-rich.

Question 69

True/False
Erupting lavas generally have a temperature in the range of 700 ° to 1200 ° F.

Question 70

The mineral having the lowest melting point in the Bowen's reaction series is olivine.

Question 71

Aphanitic, phaneritic, and porphyritic are textural terms that:

A) refer to fine-grained, coarse-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) refer to fine-grained, course-grained, and mixed-grained crystal sizes, respectively, AND are indicative of volcanic, plutonic, and mixed plutonic-volcanic origins, respectively.
E) all of these

Question 72

A vesicular felsic rock is called a:

A) pumice.
B) rhyolite.
C) obsidian.
D) basalt.
E) breccia.

Question 73

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 the these

Question 74

Natural glass, such as obsidian, forms when magma:

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 75

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

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

Question 76

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

Question 77

Hot-spot volcanism is likely the result of

A) a subduction zone.
B) rifting.
C) strike-slip movements.
D) a mantle plume.
E) none of these

Question 78

Bowen's reaction series explains the order of mineral formation with decreasing temperature.

Question 79

Multiple Choice 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 ground AND form by crystallization and intrusion of magma into surrounding rocks
E) solidify above the ground AND form by crystallization and intrusion of magma into surrounding rocks

Question 80

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.