Deck 4: Igneous Rocks and Intrusive Igneous Activity

Question 1

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

Answer 1

Basalt and gabbro are both felsic rocks,but basalt is aphanitic due to rapid cooling and gabbro is phaneritic due to slower cooling.The same is true for composition but not cooling rate of andesite,the fine-grained,and diorite,the coarse-grained,equivalents.Rhyolite is a fine-grained,rapid cooling felsic rock,and granite is a coarse-grained,slow cooling felsic rock too.Basalt,andesite,and rhyolite are increasingly felsic fine-grained rocks,and gabbro,diorite,and granite are increasingly felsic coarse-grained rocks.The first set is extrusive,and the second set is intrusive.

Question 2

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

Answer 2

Felsic magma has more than 65% silica,mafic magma is less than 52% silica,and intermediate magma falls in between.Sodium,potassium,and aluminum are higher in the more silica-rich magmas.Calcium,iron,and magnesium are lower in the more silica-rich magmas.

Question 3

What are pegmatites,and how do they form?

Answer 3

Pegmatites are composed of mostly felsic minerals,close in composition to granite.The minerals in pegmatites are enormous,at least 1 cm across and up to many centimeters or even meters.Pegmatites are found near large granite plutons and form from the water-rich magma that remains after most of the granite crystallized.The water-rich magma travels through cracks and has time to cool slowly,creating enormous minerals.

Question 4

What are the effects of assimilation on magma composition?

Question 5

What are the effects of magma mixing on magma composition?

Question 6

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

Question 7

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

Question 8

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

Question 9

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

Question 10

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

Question 11

How do volcanic necks form?

Question 12

Briefly explain batholith formation.

Question 13

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

Question 14

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

Question 15

What are dikes,sills,and laccoliths?

Question 16

What causes the volcanism at spreading ridges?

Question 17

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

Question 18

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?

Question 19

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

Question 20

What phenomena does Bowen's reaction series help explain?

Question 21

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

Question 22

Why does lava retain heat so well?

Question 23

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

Question 24

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

Question 25

What is an igneous rock?

Question 26

What is a pluton?

Question 27

What are flood basalts?

Question 28

How does a batholith differ from a stock?

Question 29

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

Question 30

What is viscosity?

Question 31

Explain how batholiths and stocks formed via plate tectonics.

Question 32

Explain how a laccolith is similar to a sill.

Question 33

How does lava differ from magma?

Question 34

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

Question 35

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

Question 36

How does a dike differ from a sill?

Question 37

What role does stoping play in the emplacement of batholiths?

Question 38

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

Question 39

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

Question 40

Why do pegmatite mineral crystals grow so large?

Question 41

When magma cools rapidly,nucleation (increases/decreases)____________________,the rate of crystal growth (increases/decreases)____________________,and the resulting rock is ____________________-grained.

Question 42

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

Question 43

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 44

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

Question 45

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

Question 46

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 47

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

Question 48

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

Question 49

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

Question 50

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

Question 51

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

Question 52

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

Question 53

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

Question 54

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

Question 55

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

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

Question 57

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

Question 58

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

Question 59

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 60

____________________ are concordant,mushroom-shaped plutons.

Question 61

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

Question 62

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

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

Question 63

The lowest temperature mineral on Bowen's reaction series is olivine.

Question 64

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 65

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

Question 66

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 67

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)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 68

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 69

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 70

A vesicular felsic rock is called a:

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

Question 71

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

Question 72

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 73

Hotspot 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 74

Most igneous rocks are classified by:

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

Question 75

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 76

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 77

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 78

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

Question 79

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

Question 80

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.