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Rocks are made of Minerals
(Minerals in Granite)
Rocks
The Geologic Dictionary
Rock Cycle
Rock Identification is based on:
• Composition
What minerals make
up the rock?
• Texture
What is the shape, size
and orientation of the
mineral grains that
make up the rock?
Major Difference:
Crystalline vs. Clastic
Proportions of Rock Types on the Earth
Soil, sediment,
weathered rock,
regolith
Igneous Composition
Igneous
Rocks
Mafic
Identification
Felsic
Igneous Textures - Crystalline
Coarse Grained
Igneous Textures - Crystalline
Fine Grained
Porphyritic
Groundmass
Phenocrysts
Igneous Textures - Crystalline
Igneous Textures - Pyroclastic/Fragmental
Glassy
Made of rock fragments
rather than crystals
Vesicular
Ultramafic Rock
- Dunite
Igneous Rocks
Mafic
Intermediate
Diorite
Granodiorite
Felsic
Granite
Fine Coarse
Gabbro
Andesite
Basalt
Dacite
Rhyolite
Igneous
Rocks
Sir James Hall
Scottish Geologist
(1761 - 1832 )
Interpretation
Igneous Rock “Translations”
• Composition
(Mafic v. Felsic)
• Magma source
• Texture
Grain Size, etc.
• How quickly and where
magma cooled
Magma Source: Partial Melting
Hypothetical Solid Rock:
Intermediate Composition
Mineral
Temperature = 500°C
Melting
Temp
A (Mafic)
1200°C
B (Int)
1000°C
C (Felsic)
800°C
Magma Source : Partial Melting
Magma Source : Partial Melting
Melting
Temp
Mineral
Intermediate Magma
(All Minerals Melt)
A (Mafic)
1200°C
A (Mafic)
1200°C
B (Int)
1000°C
B (Int)
1000°C
C (Felsic)
800°C
C (Felsic)
800°C
Temperature = 1400°C
Temperature = 900°C
Melting
Temp
Mineral
A (Mafic)
1200°C
B (Int)
1000°C
C (Felsic)
800°C
More Mafic
Magma
Bottom Line on Partial Melting
Felsic
Magma Separates
Remaining Rock:
Melting
Temp
Mineral
Partial Melting produces a magma that is
more felsic than the parent rock
Rock
Ultramafic
Mafic
Intermediate
Felsic
Magma from Partial Melting
Mafic
Intermediate
Felsic
(more) Felsic
Magma
Temperature = 900°C
Composition: Magma Source
Mafic
Intermediate
Composition: Magma Source
Felsic
Mafic
Intermediate
Felsic
Ultramafic mantle
Source: Partial Melting of ultramafic mantle at
Divergent Zones and…
Source: Partial Melting of ultramafic mantle at
Divergent Zones and … Hot Spots
Composition: Magma Source
Mafic
Intermediate
Composition: Magma Source
Felsic
Source: Partial Melting of mantle, ocean crust and continent at
Subduction Zones
Grain Size:
Plutons and Volcanoes
Mafic
Intermediate
Felsic
Source: Partial melting felsic continent above
Hot Spots & Subduction Zones
Name this Igneous Feature…
Fine
Grained
Igneous Dike
Coarse
Grained
Plutonic Structures
Why do we find Plutons at the Surface?
Inclusions: Xenoliths
Uplift & Erosion
Source: William E. Ferguson
Sierra Nevada Mountains Batholith, California
Intermission: Quiz
Intermission: Quiz
What Can you say about the history of this rock?
What Can you say about the history of this rock?
Magma produced by
partial melting of the
mantle that erupted
from a volcano at a
divergent zone or hot
spot.
Magma produced by
partial melting of the
mantle that cooled
underground (plutonic)
at a divergent zone or
hot spot.
Gabbro
http://itc.gsw.edu/faculty/tweiland/basalt.jpg
Basalt
Intermission: Quiz
Intermission: Quiz
What Can you say about the history of this rock?
What Can you say about the history of this rock?
Magma produced by
partial melting of the
continental crust that
cooled underground
(plutonic) at a
subduction zone or
continental hot spot.
Granite
Magma produced by
partial melting of the
mantle, ocean crust &
continental crust, that
erupted from a volcano
at a subduction zone.
Andesite