igneous rocks and volcanoes (LEC 3)

Question 1

what is geothermal gradient

Answer 1

the rate of temperature increase with depth within the earth

Question 2

the highest rate of temperature increase is in the crust

Answer 2

the rate of temperature increase in the crust is about 25 C/km

Question 3

difference between magma and lava

Answer 3

lava: molten rock that extrudes to the earth’s surface
magma: molten rock that remains under the earth’s surface

Question 4

if magma or lava cools, it will solidify to form…

Answer 4

igneous rocks

Question 5

If magma solidifies, ________ (_______) igneous rocks form

Answer 5

intrusive (plutonic)

Question 6

if the lava solidifies, ________ (_______) igneous rocks form

Answer 6

extrusive (volcanic)

Question 7

when magma solidifies below the
crust, the cooling rate is _____ making _________-grained rocks

Answer 7

slow
coarse

Question 8

when lava solidifies at the earth’s surface the cooling rate is _____ making _________-grained rocks

Answer 8

rapid
fine

Question 9

factors affecting the melting of rocks

Answer 9

• temperature
• confining pressure
• volatiles

Question 10

what happens if the confining pressure drops

Answer 10

the melting point lowers, and the rock melts at a lower temperature and
this mechanism called decompression melting

Question 11

decompression melting

Answer 11

produces magma along the ocean ridges where plates are rifting apart

Question 12

presence of volatiles (water vapour, CO2, SO2) INCREASES the melting point of rocks
true/false

Answer 12

false they decrease the melting point

Question 13

main conditions for magma generation

Answer 13

• heat, increasing temperature
• decrease in pressure, decompression melting
• introduction of volatiles (mainly water) can reduce the melting point

Question 14

what is eutectic temperature

Answer 14

eutectic temperature is the lowest possible melting temperature for the comprising minerals

Question 15

most magmas consist of three parts:

Answer 15

liquid, solid, and gas

Question 16

the liquid magma is called the _____ and is comprised of _______ & ________

Answer 16

melt
silicon & oxygen

Question 17

what are the three magma characteristics:

Answer 17

• magma has a range of compositions
• magma has high temperature
• magma has the ability to flow

Question 18

increasing the temp of magma does what to its viscosity
increasing the silica content of magma does what to its viscosity

Answer 18

decreases viscosity
increases viscosity

Question 19

as silica content increases, viscosity increases, which one is more viscous: mafic or felsic

Answer 19

felsic magma

Question 20

what are the four types of magma

Answer 20

ultramafic
mafic
intermediate
felsic

Question 21

a single magma can generate rocks with different compositions, why

Answer 21

*diversity of chemical composition of magma
*variation in melting points of different minerals

Question 22

who is norman bowen

Answer 22

scientist who identified the sequence in which minerals crystallize from magma

Question 23

magmatic differentiation

Answer 23

refers to formation of one or more secondary
magmas from the parent magma, those secondary magmas have
different chemical composition from the parent magma

Question 24

mechanisms of magmatic differentiation

Answer 24

1. crystal settling
2. assimilation
3. magma mixing

Question 25

which type of magma has the least amount of silica content but the highest melting point

Answer 25

ultramafic magma

Question 26

mafic rocks are darker and denser than the felsic rocks because of their high content of Fe and Mg, true/false

Answer 26

true

Question 27

most lava are from mafic magmas or felsic magmas

Answer 27

mafic magmas

Question 28

felsic rocks are mainly intrusive (plutonic), why

Answer 28

felsic magmas are more viscous than mafic magmas, and thus they usually lose their mobility before reaching the surface. furthermore, the melting temp of felsic magma (650oC) is lower than mafic magma
(1000C)

Question 29

when there’s slow cooling crystals become large/small?
when theres rapid cooling crystals become large/small?

Answer 29

large
small

Question 30

what are the 7 types of igneous texture

Answer 30

aphanetic
phanertic
porphyritic
vesicular
glassy
pyroclastic
pegmatitic

Question 31

aphanetic

Answer 31

fine grained
rapid cooling
minerals are not visible with naked eye

Question 32

phaneritic

Answer 32

coarse-grained
slow cooling
minerals are visible to naked eye

Question 33

vesicular

Answer 33

contains voids in rock

Question 34

porphyritic

Answer 34

thousands of years to cool
two different crystal sizes

Question 35

glassy

Answer 35

very rapid cooling
no crystals

Question 36

pyroclastic

Answer 36

consist of fragments that are ejected during a violent volcanic eruption

Question 37

pegmatitic

Answer 37

very coarse grained rock

Question 38

igneous rocks are classified based on their ________________ and _________________

Answer 38

composition and texture

Question 39

two rocks may have similar compositions but different textures, thus different names
example: granite - rhyolite

Answer 39

wowwwwwwww O__O incredible!!

Question 40

majority of igneous rocks are intrusive/extrusive

Answer 40

intrusive (plutonic)

Question 41

shape of igneous rocks: what does tabular and massive mean

Answer 41

flat and shapeless

Question 42

orientation of igneous rocks: what does concordant and discordant mean

Answer 42

if they are parallel to sedimentary rocks
if they are not parallel to sedimentary rocks

Question 43

dykes are tabular/massive and concordant/discordant
sills are tabular/massive and concordant/discordant

Answer 43

tabular discordant
tabular concordant

Question 44

laccoliths are tabular/massive
batholiths are tabular/massive

Answer 44

both are massive

Question 45

is the distribution of volcanoes across the globe random where can active volcanoes be found
circum-pacific belt
deep oceanic basin
intraplate volcanism

Answer 45

circum-pacific belt (ring of fire)