Deck 4: Igneous Rocks and Plutons

Question 1

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

Answer 1

True

Question 2

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

Answer 2

False

Question 3

Crystal settling involves gravitational settling of melted minerals.

Answer 3

False

Question 4

When plutons begin to form and crystallize to form minerals, fluids emanating from them follow cracks and crevasses in adjacent rocks where ____.

A)mineral resources such as copper may form
B)they escape from the atmosphere and cause air pollution
C)they form volcanic lakes
D)geologists are able to accurately measure underground temperature
E)they rupture Earth's surface and form faults

Question 5

A key characteristic of igneous rocks is that they ____.

A)are the youngest rocks on Earth
B)are made up of minerals that crystallized from molten rock matter called magma
C)never contain iron or magnesium
D)are not as hard as sedimentary rock
E)always contain more than three different mineral types

Question 6

Plutons originate through ____ activity.

A)extrusive igneous
B)extrusive volcanic
C)igneous volcanic
D)intrusive igneous
E)intrusive volcanic

Question 7

Many geologists now think that hot-spot volcanism results from a rising mantle plume.

Question 8

Pyroclastic igneous rock forms from ____.

A)explosive volcanic activity
B)rapidly cooling plutons
C)viscous lava flows
D)basalt and gabbro
E)melting of country rock

Question 9

Magmas with the highest percentages (> 65%)of silica are called ____.

A)mafic
B)felsic
C)intermediate
D)ultramafic
E)ultrafelsic

Question 10

Melting of Earth's crust yields mostly silica-rich magmas because ____.

A)the most abundant minerals in Earth's crust are silicates
B)silica is more easily melted than other minerals
C)many minerals produce silica when melted
D)silica has extremely low viscosity and move quickly up to Earth's crust from far underground
E)when silicon reacts with sodium chloride it form silica

Question 11

Obsidian, a variety of volcanic glass, may be black, dark gray, red, or brown, depending on the presence of iron.

Question 12

Mafic lava tends to be fluid, whereas felsic lava is much more viscous.

Question 13

Partial melting of oceanic crust and silica-rich sediments of continental margins ____.

A)yields magma richer in basalt than the source rock
B)is a major cause of earthquakes
C)causes off-gassing which increases global warming
D)yields magma richer in silica than the source rock
E)will form sedimentary rock

Question 14

The process of assimilation excludes any incorporation of felsic country rock in the newly formed rock.

Question 15

Basalt and gabbro are compositional equivalents, which means that they ____.

A)are both formed from the same pluton
B)have the same texture but are made up of different minerals
C)are made up of the same minerals and are the result of explosive igneous activity
D)are made up of the same minerals but have different textures
E)have the same texture but one is mafic and the other is felsic

Question 16

Batholiths are large plutonic bodies produced by a single, voluminous intrusion of magma in a region.

Question 17

An igneous rock with no visible crystals ____.

A)has a phaneritic texture
B)cooled quickly in a magma chamber
C)slowly on Earth's surface
D)cooled quickly on Earth's surface
E)is granite

Question 18

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

Question 19

Most lava temperatures are taken at volcanoes that show little or no explosive activity because ____.

A)their mafic flows give more accurate average temperatures
B)these volcanoes are extremely rare and, therefore, more interesting
C)explosive volcanoes cannot be approached safely
D)their felsic flows give more accurate average temperatures
E)these volcanoes are extremely common and, therefore, measured more frequently

Question 20

Basalt and gabbro are the rocks that crystallize from mafic magma.

Question 21

Volcanoes have a cylindrical conduit know as a volcanic ____ that connects to an underlying magma chamber.

A)neck
B)tube
C)funnel
D)pipe
E)cord

Question 22

One example of a vesicular felsic rock is ____.

A)pumice
B)basalt
C)obsidian
D)granite
E)mica

Question 23

Most plutons form ____.

A)well within plates
B)from extruded lava
C)from batholiths
D)above the land surface
E)at convergent plate boundaries

Question 24

Aphanitic, phaneritic, and porphyritic are terms that indicate ____, respectively.

A)fine-grained, course-grained, and mixed grained crystal sizes
B)formation by fast cooling, slow cooling, and mixed cooling rates
C)plutonic, volcanic, and mixed plutonic-volcanic origins
D)course-grained, fine grained, and mixed grained crystal sizes
E)Mixed-grain, course-grained, and fine-grained crystal sizes

Question 25

Natural glass such as obsidian forms when ____.

A)magma cools too rapidly for crystals to form
B)pegmatite melts, moves to Earth's surface and ,re-forms
C)magma cools too slowly for crystals to form
D)magma has a very low silica content
E)gas escapes through lava

Question 26

A laccolith forms when a sill ____ and causes the overlying rocks to ____.

A)ruptures underground; collapse
B)inflates; bow upwards
C)deflates; melt
D)breaks the surface; explode
E)becomes a dike; tilt 90 degrees

Question 27

The process of assimilation ____.

A)includes melting and incorporation of inclusions of country rock
B)includes the inclusion of country rock in an extrusive magma
C)occurs in all plutons
D)results in additional heating of a magma body
E)separates mafic rock from felsic rock

Question 28

Although all compositions are represented, most plutons are ____ rocks.

A)felsic
B)intermediate
C)mafic
D)pyroclastic
E)basaltic

Question 29

Both batholiths and stocks are ____.

A)mostly discordant
B)not considered plutons
C)found in South America
D)always exposed at the surface via erosion
E)unable to follow Bowen's reaction series because of their size and depth

Question 30

Large crystals found in a fine-grained groundmass can indicate a(n)____.

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

Question 31

Igneous rocks formed by explosive volcanic activity have a texture that is ____.

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

Question 32

The intrusive igneous rocks that most likely formed below Earth's surface are ____.

A)basalt, pumice, and welded tuff
B)obsidian, granite, and basalt
C)pumice, andesite, and welded tuff
D)granite, diorite, and gabbro
E)granite, diorite, and rhyolite

Question 33

Most igneous rocks are classified as either volcanic or plutonic based on their ____.

A)size and location
B)magnesium content
C)iron content
D)texture and composition
E)size and composition

Question 34

Mantle plumes are primarily found at ____.

A)divergent plate boundaries
B)convergent plate boundaries
C)transform plate boundaries
D)at the core-mantle boundary
E)Earth's surface

Question 35

Stoping is the process in which ____.

A)pyroclastic flows are tranformed into obsidian
B)rising magma detaches and engulfs pieces of country rock
C)the viscosity of magma changes due to changes in silica content
D)dikes are formed due to intense heat in the country rock
E)erosion exposes batholiths

Question 36

Most batholiths ____.

A)assimilate all country rock as they move upward
B)form during a volcanic eruption
C)are composed of obsidian and pumice
D)have a pyroclastic texture and are usually small geological features
E)were emplaced by forceful injection and stoping as magma moved upward

Question 37

A(n)____ pluton has boundaries that parallel the layering in the country rock.

A)concordant
B)discordant
C)correspondent
D)analogous
E)disruptive

Question 38

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 39

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

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

Question 40

Igneous rocks that most likely have a two-stage intrusive-extrusive origin have a(n)____ texture.

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

Question 41

Discuss three (3)mechanisms of magma origination.

Question 42

Discuss how Bowen's reaction series helps explain the composition of many igneous rocks.

Question 43

Compare and contrast dikes and sills.

Question 44

Why are rhyolite flows less common than basalt flows?

Question 45

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

Question 46

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

Question 47

Why do holes form in vesicular igneous rocks?

Question 48

You are given a specimen of rhyolite and a specimen of granite. What method would you use to differentiate them? How can you tell which specimen is more likely volcanic and which is more likely plutonic? Include the terms phaneritic and aphanitic in your answer.

Question 49

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

Question 50

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

Question 51

The largest plutons are called ____________________ and are made up primarily of ____________________ igneous rocks.

Question 52

Basalt cooled from ____________________, whereas granite cooled from ____________________.

Question 53

Rapid cooling of magma results in a fine-grained ____________________ texture. Slow cooling of magma results in a course-grained ____________________ texture.

Question 54

Distinguish between rhyolite tuff and welded tuff.

Question 55

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

Question 56

____________________ are concordant, mushroom-shaped plutons.

Question 57

How are subduction and the origin of magma related?

Question 58

The term pegmatite refers to an igneous rock with a particular ____________________ rather than a specific ____________________.