Igneous Rocks

Question 1

What is the difference between magma and lava?

Answer 1

Both are hot liquid rock with crystals, fragments of rock, and gas, but lava exists at the surface of the earth, while magma resides below.

Question 2

Three ways to melt a rock

Answer 2

Raise Temp, lower pressure, move the phase boundary

Question 3

What three main locations generate magma and igneous rocks?

Answer 3

hotspots, spreading ridges, and subduction zones

Question 4

How do spreading ridges melt rock?

Answer 4

They increase temperature and significantly decrease the pressure. (decompression melting)

Question 5

How do subduction zones melt rock?

Answer 5

The presence of water shifts the melting point of rock down, and partial melting can occur at lower temperatures (flux melting)

Question 6

lava that crystallizes form what kind of rocks?

Answer 6

extrusive rocks (volcanic)

Question 7

Magma that crystallizes before reaching the surface forms what kind of rocks?

Answer 7

intrusive (plutonic)

Question 8

How are igneous rocks classified?

Answer 8

texture (grain size) and chemical composition

Question 9

What is the texture of volcanic rocks?

Answer 9

Fine grained to glassy

Question 10

What is the texture of plutonic rocks

Answer 10

coarse grained (slow cooling)

Question 11

Give an example of ultramaific material

Answer 11

mantle (low in silica)

Question 12

Give an example of mafic material

Answer 12

basalt, oceanic crust

Question 13

Give an example of felsic material?

Answer 13

granite, high in silica

Question 14

What is Bowens Reaction Series?

Answer 14

Minerals crystalize and settle out of magma in a definite sequence, starting with olivine and certain feldspars, and ends with quartz. RULE: mafic materials crystalize first, felsic materials crystalize last.

Question 15

Define viscosity

Answer 15

resistance to flow

Question 16

What has higher viscosity, felsic or maific magma?

Answer 16

felsic (more silicates)

Question 17

What defines mafic lava flow? (3)

Answer 17

1. large, lower viscoisty flows. 2. less explosive eruptions. 3. low ratio of pyroclastic sediment to lava

Question 18

What defines felsic lava flow? (3)

Answer 18

1. smaller, higher viscosity lava flows. 2. explosive eruptions. (since lava is thick and can build a lot of pressure before finally erupting) 3. High ratio of pyroclastic sediment to lava

Question 19

Define pyroclastic sediment

Answer 19

 broken up particles of rocks and minerals deposited during volanic eruption

Question 20

What makes shield volcanoes

Answer 20

The low viscosity of mafic magma

Question 21

What makes stratovolcano

Answer 21

felsic, high viscosity of lava

Question 22

what kind of magma does a mid-oceanic ridge produce>?

Answer 22

maific magma, since there is little fractionation

Question 23

What is fractionation?

Answer 23

time spent in magma chamber, so the longer you are there, the more minerals that can crystalize out

Question 24

What kind of magma is made by island arc volcanoes?

Answer 24

mafic to intermediate magma produced

Question 25

what kind of lava is produced in continental margin volcanoes?

Answer 25

maific to felsic magma

Question 26

what kind of magma is produced by hotspots?

Answer 26

mafic (oceanic ones) to mafic and felsic magma (continental hotspots)

Question 27

Many igneous rocks crystallize at great depth in the Earth’s crust.
How is it possible that these rocks are exposed at the Earth’s surface
today?

Answer 27

Tectonic uplift and erosion

Question 28

. Lava generates

a) igneous rock with small crystals.
b) stratovolcanoes, not shield volcanoes.
c) most granite in the crust.
d) None of the above.

Answer 28

a

Question 29

Flux melting generates magma at

a) subduction zones
b) spreading ridges
c) hotspots
d) All of the above

Answer 29

a

Question 30

Decompression melting generates magma at

a) subduction zones
b) spreading ridges
c) hotspots
d) All of the above.

Answer 30

b

Question 31

Partial melting generates magma at

a) subduction zones
b) spreading ridges
c) hotspots
d) All of the above.

Answer 31

d

Question 32

Crystallization in a cooling magma

a) proceeds according to Bowen’s reaction series.
b) commonly causes the magma to become more felsic over time.
c) can explain compositional differences between some igneous rocks.
d) All of the above.

Answer 32

d

Question 33

The viscosity of a magma increases with

a) decreasing silica content.
b) increasing volatile content.
c) increasing temperature.
d) None of the above

Answer 33

d

Question 34

Relative to felsic magmas, mafic magmas tend to be associated with

a) larger, lower-relief volcanoes.
b) a less-explosive style of volcanism.
c) volcanoes with a lower ratio of pyroclastic sediment to lava.
d) All of the above.

Answer 34

d

Question 35

Sedimentary rocks cover ~75% of Earth’s surface, but only account for
~10% of the weight of the crust because…
a) they can be converted to igneous rocks at depth.
b) they form at the Earth’s surface.
c) they can be converted to metamorphic rocks at depth.
d) All of the above

Answer 35

d