The Rock Cycle
Igneous Rock
Solidification
Magma
Partial Melting
Mantle Rock Fig 3.1
Geological Materials
Transformation Processes
Formation of Magma
How are rocks melted? 1. Heating 2. Depressurization 3. Partial Melting
Where do rocks melt? Subduction zones (Silicic
and Intermediate)
Mantle Plumes or Hot Spots
Partial Melting Different rocks melt
at different temperatures.
Depending on the temperature, some rocks in the mixture may be liquidified and others might not.
Intrusive Course grained
rock that cooled slowly under the surface.
This is the most common type of rock.
Also describe as Plutonic
See Kehew, Fig 3-6
Classification of Igneous Rocks
These classes of rock are based on the type of magma that cooled to create the rock.
These are describe in terms of temperature, composition, viscosity, and pH level.
Silicic (a.k.a, felsic) Magmas Cool (<700oC) Viscous (sticky, doesn’t flow easily) Gaseous (steam of H2O and C02)
Silicic Rocks Usually intrusive, course-grained, Silicic (Granite) to Intermediate
(Diorite). If extrusive, fine-grained rocks
formed by explosive volcanoesRhyolite or Andesite Volcanoes
Silicic Rocks
Intrusive Silicic Igneous RockE.g., Granite (Silicic, Phaneritic):
Crystallized (Solidified) Silicic Magma Poor in: Fe, Mg,
Ca, (<20%) Rich in: Silica
(>70%)
Quartz
Na Plagioclase
Biotite
Mafic Rocks
Mafic Magmas Hot (>1000oC) Non-Viscous (runny, flows easily) “Dry” (no H2O or C02)
Mafic Rocks Usually Extrusive, Fine-grained,
Mafic (Basalt) rock forms oceanic crust, Shield Volcanoes and Basalt Floods
If Intrusive, course-grained mafic rocks are formed Gabbro.
If intrusive, Dikes and Sills more common
See Kehew, Fig 3-40
Hawaii
10.3 12.0
20.6
Midway 27.2 19.9 43.4
42.4
48.1 55.2
56.2 59.6
0-5
Current PlateMotion
HawaiiA long chain of inactive volcanoes Island ages, millions of years
Shield Volcanoes
Mafic Magma Low-viscosity Non-explosive eruptions Gentle slopes Covering large areas
Types of Eruptions (Mafic Volc.)
Types of Eruptions Lava floods Lava fountains Fissure eruptions
Rock Textures (Table 3-1)
Aphanitic Porphyritic Vesicular Glassy (Obsidian)
Surface Textures (Extrusive, Mafic Rocks)
Ahah (Rubbley) Mostly solid when
flowing Pahoehoe (Ropey)
mostly liquid when flowing)
Mafic Sill: Intruded between layers Mafic magma is less
viscous and hotter so Does not form plutons
but Cuts along layers (Sills)
or even across layers (Dikes) Also Baked Zones
of adjacent country rock and Chill Zones within the intrusion
Igneous Rock ClassificationIntrusive (Plutonic)
Extrusive (Volcanic)
Min
eral
Per
cen
tag
e
Continental Crust Oceanic Mantle Crust
Igneous Rock Classification Silicic Intermediate Mafic
Granite Diorite Gabbro
Rhyolite Andesite Basalt
(Porphyritic)
Intr
usi
veE
xtru
sive
1200
oC
1000
o
Bowen’s Reaction SeriesTwo series of minerals formed during crystallization of magma
Intrus. Extrus.
Gabbro Basalt
Diorite Andesite
Granite Rhyolite
Low Silica Magma
High Silica Magma
Fra
me-
D
oubl
e
S
ingl
e
Isol
ated
wor
k
S
heet
Cha
in
Cha
in
Temperature ofCrystallization
750
o
Bowen’s Reaction Series
Illustrates the relationship between the cooling magma and the crystallization of the minerals contained in the rock.
Rocks on the right side of this chart are rich in calcium and sodium
Rocks on the left side represents iron-rich minerals. They cool and create quartz.
Terminology
Felsic – silicate minerals, magmas and rocks enriched in lighter elements for oxygen, aluminum, sodium, and silicon.
Aphanitic – dark-coloured rock where the grains are so fine they cannot be seen by the naked eye.
Terminology
Mafic – iron and magnesium enriched minerals are found in these rocks. They are dark in colour.
Phaneritic – Grains in the rock can be seen by the naked eye.
Types of Igneous Rocks
Granite Acidic Very pale Coarse-grained Intrusive, felsic Can be pink to dark
gray.
Andersite
Intermediate rock Less quartz that
granite, thus has a darker colour.
Both sizes of grains. Not as acidic as
Granite. Found in the Andes Extrusive
Basalt
Black to gray in colour (dark)
Fine-grained Mafic Found in Ireland
(Giants Causeway) and Hawaii.
Basic Extrusive
Pumice
Glassy (Frothy) Light to dark in colour
depending on its impurities.
Solidified foam Extrusive
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