igneous rocks

Question 1

coherent, naturally occuring solid, composed of an aggregate of minerals

Answer 1

definition

rock

Question 2

1. decompression melting
2. fluid induced melting
3. within plate magmatism (mantle plume)

Answer 2

melting scenarios

plate tectonic framework

Question 3

• extrusive rocks - crystallization of lava that erupt at the surface
• intrusive rocks - crystallize the magma at depth

igneous rocks

Answer 3

igneous system

extrusive vs. intrusive

Question 4

1. preexisting rocks melt (or partially melt) forming magma
2. melt is transported to shallow levels as it is less dense than source rock
3. magma cools and minerals crystallize

Answer 4

igneous system

Question 5

• plutonic rocks
• large, interlocking crystals (due to slow cooling)

e.g. granite

Answer 5

intrusive rocks

Question 6

• volcanic rocks
• fined-grained or glassy texture (due to rapid cooling)

e.g. basalt

Answer 6

extrusive rocks

Question 7

quartz, feldspar, mica, pyroxene, amphibole, olivine

Answer 7

igneous rocks

common minerals

Question 8

formed when magma intrudes into a crack or fissure and solidifies at a verticle angle (relative to the pre-existing rock layers)

Answer 8

intrusive structures

dike

Question 9

formed when magma exploits a weakness between layers in bedrock and solidifies parallel to the sedimentary layers

Answer 9

intrusive structures

sill

Question 10

a mass of intrusive igneous rock, often somewhat round

e.g. Half Dome, Yosemite National Park, now exposed by erosion

Answer 10

intrusive structures

pluton

Question 11

small scale geometric relationships between crystals in a rock sample

Answer 11

classification of igneous rocks

texture

Question 12

course grain rock, can see crystals/minerals with naked eye

igneous rock texture, e.g. granite

Answer 12

igneous rock texture

phaneritic

Question 13

fine grained rock, cannot see crystals/minerals with the naked eye

igneous rock texture, e.g. basalt

Answer 13

igneous rock texture

aphanitic

Question 14

large crystals in a fine matrix

igneous rock texture

Answer 14

igneous rock texture

porphyritic

Question 15

bubbly or frothy

igneous rock texture

Answer 15

igneous rock texture

vesicular

Question 16

fragmental

igneous rock texture

rock formed from large deposits of tephra fragments is called tuff

Answer 16

igneous rock texture

pyroclastic

Question 17

mineral composition of the rock (most commonly used) or chemical composition (better for volcanic rocks)

Answer 17

classification of igneous rocks

composition

Question 18

mainly feldspar, quartz, mica (lighter in colour)

e.g. granite (intrusive), rhyolite (extrusive)

higher silica, low in Fe and Mg

Answer 18

compostition of igenous rocks

felsic

Question 19

equally rich in felsic and mafic minerals (grey in colour)

e.g. diorite (intrusive), andesite (extrusive)

medium silica

Answer 19

compostition of igenous rocks

intermediate

Question 20

mainly plagioclase, pyroxene, olivine, amphibole, and biotite (darker in colour)

e.g. gabbro (intrusive), basalt (extrusive)

high in Ma and Fe, lower silica

Answer 20

compostition of igenous rocks

mafic

Question 21

almost all olivine and pyroxene

e.g. peridotite (intrusive), komatiite (extrusive)

very low silica, common in mantle

Answer 21

compostition of igenous rocks

ultramafic

Question 22

mafic to intermediate (intrusives, extrusives)

Answer 22

formation of igneous rocks

island arc plate subduction

Question 23

basaltic (extrusive, intrusives)

Answer 23

formation of igneous rocks

plate divergence

mid ocean ridges

Question 24

basaltic (extrusives, intrusives)

Answer 24

formation of igneous rocks

hot spot volcanism

Question 25

mafic to felsic (intrusives, extrusives)

Answer 25

formation of igneous rocks

continental plate subduction