5 igneous rocks

Question 1

magma vs lava

Answer 1

Magma: molten rock beneath the Earth’s surface
Lava: molten rock above the Earth’s surface

Question 2

generation of magma

Answer 2

Magma is formed by melting pre-existing solid rock
Movement of magma is DENSITY-driven
Lava lamps are groovy
And scientific!
Heat source
Geothermal gradient
Deeper you go, hotter you get
Lava lamp light
Cooling area
Earth’s crust
Top of lava lamp
Hot and less dense
Molten Rock
Hot wax near the light

Question 3

Types of magma melting

Answer 3

Two main types of melting:
Decompression melting
Flux melting (aka dehydration melting)
One subtype
Heat transfer melting
Triggered by either decompression or flux melting

Question 4

decompression melting

Answer 4

Melting because of pressure reduction
Temperature remains the same
Divergent plate boundaries
Mantle plumes (aka hotspots)

Question 5

flux/dehydration melting

Answer 5

Flux melting (aka dehydration melting)
Melting due to the addition of water
And CO2
Convergent plate boundaries
With subduction
Continental-oceanic
Oceanic-oceanic

Question 6

Heat Transfer Melting

Answer 6

Heat transfer melting
Caused by either decompression and flux (dehydration) melting
Surrounding rocks melted by high-heat magma

Question 7

composition of a melt

Answer 7

Ultramafic melts: Silicates with highest magnesium + iron

Mafic melts: Silicates with high magnesium + iron

Intermediate melts: Silicates with intermediate blend (hence the name)

Felsic melts: Silicates with high silica and alumina

Question 8

Why is there melt variation

Answer 8

Original source rock
Amount of melting: partial or full
Assimilation of wall rock: graba and melts parts of the wall

Question 9

silicate mineral groups: felsic

Answer 9

Potassium feldspar
Plagioclase feldspar
Quartz
Muscovite mica

Question 10

silicate mineral groups: mafic

Answer 10

Olivine
Pyroxene
Amphibole
Plagioclase feldspar
Biotite mica

Question 11

Viscosity of a Melt

Answer 11

Viscosity = resistance to flow
Melt viscosity
Temperature
Hot = more fluid
Cool = more viscous
Volatiles (dissolved gases)
Higher = more fluid
Lower = more viscous
Composition
Mafic = more fluid
Felsic = more viscous

Question 12

Intrusive melt

Answer 12

Intrusive: Cooled to solid INSIDE the earth; larger crystals, slower cooling
Plutonic

Question 13

Extrusive melt

Answer 13

Extrusive: Cooled to solid OUTSIDE the earth; smaller crystals, quicker cooling
Volcanic

Question 14

Intrusive Rock Bodies

Answer 14

Classification
Based on size, shape, and relationship to the older rocks that surround them
Discordant
Cuts across older rocks
Concordant
Is in line with older rocks

Question 15

contact metamorphism

Answer 15

Baked rocks around the intrusion

Question 16

Sills and dikes: properties and differences

Answer 16

Elongate, many times longer than thick
Sills
Concordant
Dikes
Discordant

Question 17

Laccoliths

Answer 17

Medium sized
“Blister” or tree shaped
Concordant
Examples: Henry Mtns, Abajo Mtns, LaSals, Pine Valley Mtn

Question 18

plutons

Answer 18

“Blob” shaped frozen magma chambers
Discordant
Examples
Little Cottonwood Stock
ex: Salt Lake Temple Quarry, Little Cottonwood Canyon

Question 19

batholith

Answer 19

Groups of plutons that cover a large area (domes)

Question 20

volcanic necks

Answer 20

Leftover, un-erupted magma
Solidifies in volcanic vent
More resistant to erosion
Examples:
Devil’s Tower, Wyoming
Shiprock, New Mexico

Question 21

location of igneous rocks

Answer 21

Concentrated on recent and former convergent plate margins
Really old intrusive rocks in Canadian Shield
Rarely found on stable platform
Except when mantle plumes strike
ex: iceland is all igneous rocks

Question 22

Large Igneous Provinces (LIPs)

Answer 22

Large areas of mafic melts
Caused by mantle plumes
Also called “flood basalts”

Question 23

Classification of igneous rocks: chemical

Answer 23

Felsic vs Mafic
Proportion of felsic minerals to mafic minerals
Felsic minerals (light colored)
Mafic minerals (dark colored)

Question 24

Classification of gicneous rocks: texture

Answer 24

Crystal size and shape
Coarse grained
Large xls & slow cooling
Fine Grained
Small xls & fast cooling)
Pyroclastic (Fragmented)
broken crystals (explosive eruption)

Question 25

memorize and draw out igneous classification chart

Answer 25

see screenshot

Question 26

Glassy texture

Answer 26

Extrusive
No crystals
Cooled before crystals could form
Quick cooling
Typically found
Crust of lava flows
Viscous magma
Think Jolly Rancher

Question 27

Aphanitic texture

Answer 27

Extrusive
Crystals too small to be seen without a microscope
Rapid cooling
Typically found
Lava flows
Think snickerdoodle

Question 28

Phaneritic texture

Answer 28

Intrusive
Crystals large enough to be seen by the naked eye
Interlocked together
Slow cooling
Typically found
Intrusive rocks
Think oatmeal cookie

Question 29

porphyritic texture

Answer 29

Two distinct sizes of crystals

Extruive: Porphyritic aphanitic
Large crystals + microscopic crystals
Two stages of cooling: slow and then fast
Typically found in volcanic rocks
Think chocolate chip cookies

Intrusive: Porphyritic phaneritic
Large crystals + smaller crystals
Two stages of cooling: s-l-o-w-e-r and then slow
Typically found in intrusive rocks
Think oatmeal raisin cookies

Question 30

Pyroclastic texture

Answer 30

Extrusive
“Broken fire”
Made of crystals (broken), pieces of pumice (broken), rock (broken), and ash (sometimes broken)
Created from explosive volcanic eruptions
Think peanut brittle

Question 31

use chart to tell differences between pictures of igneous rocks based on color

Answer 31

see screen shots and slide 36-40