Deck 4: Igneous Rocks and Intrusive Igneous Activity

Question 1

Granites are uncommon in North America.

Answer 1

False

Question 2

Magma that cools below Earth's surface form most of the volcanoes in North America.

Answer 2

False

Question 3

Melting of crustal rocks produces silica-rich magmas.

Answer 3

True

Question 4

Mafic magma is silica poor and may be derived from melting of Earth's upper mantle.

Question 5

Magma chambers generally exist at depths of 100's of km beneath spreading ridges.

Question 6

Viscosity of a magma provides an indication of the temperature and pressure under which it crystallizes.

Question 7

Mafic magma has lower viscosity.

Question 8

Felsic lavas would tend to be slow moving, thick, and move only short distances.

Question 9

The magmas formed beneath spreading ridges are always felsic.

Question 10

Magma composition may change by crystal settling.

Question 11

Partial melting explains the origin and composition of magmas at spreading ridges but not subduction zones.

Question 12

Magmas formed at subduction zones are mostly intermediate or felsic.

Question 13

Phaneritic textures indicate that the rock formed under extrusive conditions as the lava cooled and crystallized on Earth's surface.

Question 14

Porphyritic textures suggest a complex cooling and crystallization history. one that includes at least two rates of crystallization.

Question 15

Volcanoes always erupt magmas of the same type.

Question 16

Pegmatites are composed of very large crystals that formed from water-rich magma.

Question 17

Rhyolite forms when a mafic magma cools on Earth's surface.

Question 18

Dikes are concordant and sills are discordant.

Question 19

Laccoliths are more similar to sills than they are to dikes.

Question 20

Most batholiths are emplaced by the process of granitization.

Question 21

Geologists generally agree that batholiths are emplaced by forceful injection.

Question 22

Magma that is forcefully ejected into the atmosphere as particles is known as

A) pyroclastic material
B) lava flow
C) aphanitic
D) dike rock
E) plutonic

Question 23

A magma composed of more than 65% silica is referred to as

A) mafic
B) intrusive
C) intermediate
D) extrusive
E) felsic

Question 24

The viscosity of magma is dependent on

A) temperature and depth
B) water content and depth
C) silica content and early-formed crystals
D) silica content and temperature
E) early-formed crystals and size of the magma chamber

Question 25

Plutonic rocks

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

Question 26

Aphanitic, phaneritic and porphyritic are textural terms which

A) refer to fine-grained, course-grained and mixed grained crystal sizes, respectively.
B) form from slow cooling, fast cooling, and mixed cooling rates, respectively.
C) are indicative of volcanic, plutonic and mixed plutonic-volcanic origins, respectively.
D) A and C
E) all of the above

Question 27

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) A or B
E) A and C

Question 28

Natural glass such as obsidian forms when

A) magma cools rapidly and very tiny crystals form.
B) magma cools too rapidly for crystals to form.
C) magma cools too slowly for crystals to form.
D) magma doesn't cool.
E) magma is reheated.

Question 29

Pegmatite refers to

A) an extremely coarse texture
B) an igneous rock body
C) a felsic composition
D) a mafic composition
E) A and C

Question 30

Volcanic necks form when

A) the magma abruptly cools into a solid rock column during the initial eruption
B) the eruptive material is eroded from the flanks of the volcanic pipe
C) dikes are exposed at earth's surface
D) lava fountains cool on steep volcanic slopes
E) the country rock surrounding a small stock is eroded

Question 31

A granite would form under conditions that included

A) a mafic magma cooling in the subsurface.
B) a felsic magma cooling in the subsurface.
C) a mafic magma cooling on Earth's surface.
D) a felsic magma cooling on Earth's surface.
E) none of the above.

Question 32

A basalt would form under conditions that included

A) a mafic magma cooling in the subsurface.
B) a felsic magma cooling in the subsurface.
C) a mafic magma cooling on Earth's surface.
D) a felsic magma cooling on Earth's surface.
E) none of the above.

Question 33

If early-formed crystals settled out of a magma, the magma would tend to be

A) unchanged in composition.
B) finer grained.
C) enriched in silica.
D) less viscous.
E) water soluble.

Question 34

A porhyritic texture indicates that the rock or rock body

A) initially cooled slowly, then more rapidly.
B) initially cooled rapidly, then more slowly.
C) cooled slowly, becoming enriched in silica.
D) cooled rapidly, composition staying the same.
E) has a history too complex to make any of the above statements.

Question 35

Batholiths typically contain

A) phaneritic rocks composed predominantly of ferromagnesium silicates.
B) aphanitic rocks composed predominantly of ferromagnesium silicates.
C) phaneritic rocks composed predominantly of non-ferromagnesium silicates.
D) aphanitic rocks composed predominantly of non-ferromagnesium silicates.
E) none of the above.

Question 36

A sill is a

A) concordant, tabular body of intrusive igneous rocks.
B) discordant, tabular body of intrusive igneous rocks.
C) discordant, massive body of intrusive igneous rocks.
D) concordant, tabular body of extrusive igneous rocks.
E) concordant, tabular body of intrusive igneous rocks that warps rocks upward.

Question 37

According to Bowen's reaction series, you would not find a mineral assemblage containing

A) quartz and potassium feldspar.
B) quartz and plagioclase.
C) plagioclase and amphibole.
D) quartz and olivine.
E) none of the above.

Question 38

Most magma cools___________ the surface of the earth where it forms___________.

Question 39

Magma accumulates in reservoirs known as___________

Question 40

The discontinuous branch of Bowmen's reaction series contains only ___________minerals.

Question 41

___________is the first ferromagnesian mineral to crystallize.

Question 42

By the process of___________ the composition of a magma can be changed when it comes into contact with country rock.

Question 43

When magma cools slowly, crystal growth (slows/speeds)___________ the rate of nucleation, and the resultant rock is___________ -grained.

Question 44

Ultramafic rocks are ___________found at the Earth's surface.

Question 45

The ultramafic rock composed predominately of___________ is known as peridotite, and comprises the lower ___________crust.

Question 46

Basalts are common___________ trusive rocks in the upper part of the___________crust, whereas gabbros are common ___________trusive rocks formed in the lower part of the ___________ crust.

Question 47

List two things which Bowen's Reaction Series can help explain.

Question 48

What is the evidence of forceful injection of magma as batholiths intrude into the country rock?

Question 49

List several uses for granitic rocks.

Question 50

Relative to the emplacement and exposure of granites, what do granites in Colorado, Idaho, Montana, California, and Alaska have in common?

Question 51

What are the two main categories of igneous rocks?

Question 52

Describe the role silica plays in controlling viscosity.

Question 53

What is an example of a glassy rock?

Question 54

Explain how we can tell, from a hand sample of an igneous rock, whether it formed as a volcanic rock or a plutonic rock?

Question 55

What is the rock name for a volcanic glass that is so porous it can float in water?

Question 56

Why can pegmatite mineral crystals reach such a large size?

Question 57

How do complex pegmatites differ from simple pegmatites?

Question 58

Briefly explain the two hypotheses for how complex pegmatites form.

Question 59

List some of the mineral commodities that have been recovered from pegmatites.

Question 60

Most batholiths are of what rock composition?

Question 61

Briefly explain the differences between granitization, assimilation, and forceful injection as processes of batholith emplacement.