Chapter 3

Question 1

Magma

Answer 1

Mixture of molten rock, crystals, gas, dissolved water beneath the surface of the Earth.

Question 2

Lava

Answer 2

Magma that has reached the surface.

Question 3

Partial Melt/Crystal Mushes

Answer 3

Partially molten magma and solid mineral grains. Occurs over a range of temperatures because each mineral has a different melting point.

Question 4

Felsic Magma

Answer 4

Molten rock with a high silica content, a lower melting point, and a high viscosity.

Question 5

Mafic Magma

Answer 5

Molten rock with a low silica content, a higher melting point, and a low viscosity.

Question 6

Igneous Rocks

Answer 6

Formed when molten rock solidifies in the deep crust or upper mantle.

Question 7

Intrusive (Plutonic) Rocks

Answer 7

Igneous rocks with large grains that cool slowly underground.

Question 8

Extrusive (Volcanic) Rocks

Answer 8

Igneous rocks with fine grains that cool quickly on the surface.

Question 9

Interlocking Grains

Answer 9

Crystals that grew close together

Question 10

Pyroclastic (fragmental) Texture

Answer 10

Agglomeration of broken rocks/minerals, ash, crystals welded together

Question 11

Glassy Texture

Answer 11

Rock cooled so quickly that no crystals formed.

Question 12

Vesicular Texture

Answer 12

Voids formed by bubbles of volatiles that expanded

Question 13

Phaneritic Texture

Answer 13

Slow cooling and has visible crystals.

Question 14

Aphanitic Texture

Answer 14

Fast cooling and produces fine grained rock without visible crystals

Question 15

Pegmatitic Texture

Answer 15

Large grains formed in water rich magmas with crystals often larger than 1cm.

Question 16

Porphyritic Texture

Answer 16

Mixed rate of cooling that produces a mix of large crystals and fine groundmass

Question 17

Felsic Rocks

Answer 17

Lighter in color and density. Quartz, K-feldspar, Na-rich plagioclase feldspar, muscovite/biotite

Question 18

Intermediate Rocks

Answer 18

Even mixtures of felsic and mafic properties, Na-rich plagioclase feldspar, amphibole

Question 19

Mafic Rocks

Answer 19

Darker color and higher density, Ca-rich plagioclase feldspar, pyroxene, amphibole

Question 20

Ultramafic Rocks

Answer 20

Darkest in color with the highest density, olivine, pyroxene.

Question 21

Frothy Texture

Answer 21

More bubbles than rock

Question 22

Amygdaloidal Texture

Answer 22

Voids filled with minerals

Question 23

Magma bodies/chambers

Answer 23

Melting of mantle produces mafic/ultramafic melt, which volcanoes erupt as lava with a range of compositions. Change in composition occurs in magma bodies in the crust in depth range 1 –80 km. Not usually completely molten.
Assimilation, magma mixing, crystallization and setting.

Question 24

Magmatic differentiation

Answer 24

Different minerals have different temperatures where crystals form from liquid melt. Once crystals form, they sink to the bottom.
Mafic minerals are the first to crystallize, this makes the composition of the remaining liquid more felsic. System is not in equilibrium.

Question 25

Plutons

Answer 25

Bodies of intrusive igneous rock that form underground and are visible after uplift and erosion. Classified by shape (tabular and massif), and orientation (concordant = parallel to sedimentary layers, discordant = perpendicular to sedimentary layers)

Question 26

Dykes

Answer 26

Tabular, discordant plutons.

Question 27

Sills

Answer 27

Tabular, concordant intrusion/pluton.

Question 28

Laccoliths

Answer 28

Tabular, concordant plutons that bulge upwards.

Question 29

Batholiths

Answer 29

Massif plutons with areas more than 100 km. They are usually felsic to intermediate.

Question 30

Stocks

Answer 30

Massif plutons with areas less than 100 km. Sometimes the upper part of a batholith.

Question 31

Dikes

Answer 31

Intrusions of igneous rock cutting across existing strata. Newest ones appear on top.

Question 32

Magma from heat

Answer 32

Friction as plates move, heating up of descending plate around intrusions.

Question 33

Magma from lower pressure

Answer 33

Decompression melting occurs at a divergent mid-ocean ridge and the mantle flows upwards beneath the ridge, ultramafic melt forms from molten mantle. Accumulates in a magma chamber 2 km beneath the seafloor and feeds seafloor eruptions.

Question 34

Magma from volatiles

Answer 34

Down going plate contains water that is released into the mantle of the upper plate and lowers the melting point and ultramafic melt forms. Erupts to form a volcanic arc