Igneous
IGNEOUS ROCKS
EXTRUSIVE
Volcanic- Fine-grained
INTRUSIVE
Plutonic- Coarse-grained
MAGMA
•
Molten Rock
–
Usually with dissolved gasses
•
Generated at depth
•
Eruptions if magma ( lava ) reaches surface
• If doesn’t reach surface, Solidifies underground
–
Intrudes country or host rock
–
Intrusive contact
–
Chill zone
–
Xenolith
Igneous Rocks
• Names based on mineral composition reflects chemical composition of the magma and...
Grain size
–
Very coarse -grained Pegmatitic
–
Coarse-grained: Phaneritic > 1 mm.
–
Fine-grained: Aphanitic < 1 mm.
–
Porphyritic- 2 crystal sizes
Igneous Rocks
• Names based on mineral composition reflects chemical composition of the magma and...
Grain size
–
Very coarse-grained Pegmatitic
–
Coarse-grained : Phaneritic > 1 mm.
–
Fine-grained: Aphanitic < 1 mm.
–
Porphyritic- 2 crystal sizes
Igneous Rocks
• Names based on mineral composition reflects chemical composition of the magma and...
Grain size
–
Very coarse-grained Pegmatitic
–
Coarse-grained: Phaneritic > 1 mm.
–
Fine-grained : Aphanitic < 1 mm.
–
Porphyritic- 2 crystal sizes
Igneous Rocks
• Names based on mineral composition reflects chemical composition of the magma and...
Grain size
–
Very coarse-grained Pegmatitic
–
Coarse-grained: Phaneritic > 1 mm.
–
Fine-grained: Aphanitic < 1 mm.
–
Porphyritic2 crystal sizes
•
Coarse-grained-
•
Plutonic (Intrusive)
–
Granite
–
Diorite
–
Gabbro
•
Fine-Grained
•
Volcanic (Extrusive)
–
Rhyolite
–
Andesite
–
Basalt
Igneous Rocks-
Classification
Igneous Rock Identification
• Granite (& Rhyolite)
–
High in Si + O
–
Low in Fe + Mg
–
Mostly feldspar & quartz
–
Light-colored
•
Basalt (& Gabbro)
–
“Low” in Si + O
–
High in Fe + Mg
– no quartz, abundant ferromagnesian minerals
–
Dark colored
•
Andesite (& Diorite- intermediate)
Igneous Rock Identification
• Granite (& Rhyolite)
–
High in Si + O
–
Low in Fe + Mg
–
Mostly feldspar & quartz
–
Light-colored
• Basalt (& Gabbro)
–
“Low” in Si + O
–
High in Fe + Mg
– no quartz, abundant ferromagnesian minerals
–
Dark colored
•
Andesite (& Diorite- intermediate)
Igneous Rock Identification
• Granite (& Rhyolite)
–
High in Si + O
–
Low in Fe + Mg
–
Mostly feldspar & quartz
–
Light-colored
• Basalt (& Gabbro)
–
“Low” in Si + O
–
High in Fe + Mg
– no quartz, abundant ferromagnesian minerals
–
Dark colored
•
Andesite (& Diorite- intermediate)
Chemistry of Igneous Rocks
•
Mafic rocks or magma
• Silicic (or felsic) rocks or magma
•
Intermediate rocks or magma
• Ultramafic rocks(no extrusive equivalent)
–
Dunite
– Peridotite
INTRUSIVE BODIES
(STRUCTURES)
•
Bodies that solidified undergroundPlutons
•
Volcanic neck- shallow intrusion
•
Fills cracks (joints)- tabular bodies
–
DIKE-
•
If no layering in country rock
•
If country rock is layeredDiscordant
–
SILL- less common
•
Concordantparallel to layering in country rock
INTRUSIVE BODIES
(STRUCTURES)
•
Bodies that solidified underground-Plutons
•
Volcanic neck- shallow intrusion
•
Fills cracks- tabular bodies
–
DIKE-
•
If no layering in country rock
•
If country rock is layeredDiscordant
–
SILL - less common
•
Concordant - parallel to layering in country rock
INTRUSIVE STRUCTURES
Plutons
•
BATHOLITH-
–
Large intrusive body
–
Exposed in an area greater than 100 square
Km.
–
Coalesced smaller plutons
• smaller bodies are called STOCKS
• Batholiths a gathering of smaller blobs
•
Magma moves upward from depth as diapirs
INTRUSIVE STRUCTURES
Plutons
•
BATHOLITH-
–
Large intrusive body
–
Exposed in an area greater than 100 square
Km.
–
Coalesced smaller plutons
• smaller bodies are called STOCKS
• Batholiths a gathering of smaller blobs
•
Magma moves upward from depth as diapirs
INTRUSIVE STRUCTURES
Plutons
•
BATHOLITH-
–
Large intrusive body
–
Exposed in an area greater than 100 square
Km.
–
Coalesced smaller plutons
• smaller bodies are called STOCKS
• Batholiths a gathering of smaller blobs
•
Magma moves upward from depth as diapirs
DISTRIBUTION OF
PLUTONIC- Coarse-grained
ROCK
–
Granite most abundant
•
Common in mountain ranges
•
In ancient rock that were mountain ranges that are now plains
–
Ultramafic rock in the mantle
VOLCANISM &
Igneous Activity
VOLCANISM
•
Lava = Magma at earth surface
– Silica content controls “explosiveness”
•
Pyroclasts = Fragments of rock due to explosion- Ash falls (pumice); Volcanic
Bombs (scoria)
• Lava flows
•
Extrusive rocks
• Volcano
VOLCANISM
•
Lava = Magma at earth surface
– Silica content controls “explosiveness”
•
Pyroclasts = Fragments of rock due to explosionAsh falls (pumice); Volcanic
Bombs (scoria)
• Lava flows
•
Extrusive rocks
• Volcano
VOLCANISM
•
Lava = Magma at earth surface
– Silica content controls “explosiveness”
•
Pyroclasts = Fragments of rock due to explosion- Ash falls (pumice); Volcanic
Bombs (scoria)
• Lava flows
•
Extrusive rocks
• Volcano
Effects on Humans
•
Growth of Hawaii
– 1980’s & 90’s 1.5 billion cubic meters
•
Geothermal energy- New Zealand; California
•
Effect on climate- 1816 “year without summer”
•
Volcanic catastrophies
–
Mt. St. Helens 1980
–
Vesuvius 79 AD
–
Krakatoa 1883
–
Crater Lake 6,600 y.b.p.
Effects on Humans
•
Growth of Hawaii
– 1980’s & 90’s 1.5 billion cubic meters
•
Geothermal energy- New Zealand; California
•
Effect on climate- 1816 “year without summer”
•
Volcanic catastrophies
–
Mt. St. Helens 1980
–
Vesuvius 79 AD
–
Krakatoa 1883
–
Crater Lake 6,600 y.b.p.
Mount St. Helens
•
Northern flank bulged at 1.5m/day
•
All vegetation stripped for 10km w/in seconds
•
$100s millions in damage
•
63 people died
•
Damage minimized due to prior planning by
USGS and governor
Effects on Humans
•
Growth of Hawaii
– 1980’s & 90’s 1.5 billion cubic meters
•
Geothermal energy- New Zealand; California
•
Effect on climate- 1816 “year without summer”
• Volcanic catastrophies
–
Mt. St. Helens 1980
–
Vesuvius 79 AD
–
Krakatoa 1883
–
Crater Lake 6,600 y.b.p.
Eruptive Violence &
Characteristics of Lava
•
Gas in lava
•
Viscosity
–
Temperature
–
Silica content
• Silicic lavas- most viscous
•
Mafic lavas- least viscous
Extrusive Rocks & Gases
•
Scientific study of volcanism
•
Gases
–
Primarily H
2
O
–
Also CO
2
, SO
2
, H
•
Gases & pyroclastics
2
S, HCl
–
Ashfall
–
Pyroclastic flow
Extrusive Rocks
•
Importance of silica content
•
Rhyolite- silicic
–
Predominantly feldspar and quartz
•
Andesite- intermediate
–
Plagioclase feldspar & ferromagnesian minerals
•
Basalt- mafic
–
Ferromagnesian minerals & plagioclase feldspar
Extrusive Rocks
•
Textures
–
Fine-grained (smaller than 1 mm)
–
GlassyObsidian
–
Due to
• rapid cooling (mainly)
• high viscosity
– Porphyritic
• Phenocrysts
–
Due to trapped gas
•
Vesicles
•
Scoria
• Pumice
• Textures
– Due to trapped gas
• Vesicles
•
Scoria
• Pumice
–
Fragmental
• Pyroclasts
•
Dust, ash, cinders
• Blocks & bombs
•
Tuff
•
Volcanic Breccia
Extrusive Rocks
VOLCANOES
•
Volcanoes are cone-shaped
• Vent
•
Crater
•
Flank eruption
•
Caldera
•
Types:
–
Cinder Cone, Shield, Composite
VOLCANOES
•
Volcanoes are cone-shaped
•
Vent
•
Crater
•
Flank eruption
•
Caldera
• Types:
– Cinder Cone, Shield, Composite
CINDER CONES
•
Formed of pyroclastics only
• Steep sides- ~30 degrees
•
Relatively small
• Short duration of activity
VOLCANOES
•
Volcanoes are cone-shaped
•
Vent
•
Crater
•
Flank eruption
•
Caldera
• Types:
–
Cinder Cone, Shield, Composite
SHIELD VOLCANOES
•
Low viscosity lava flows
–
Low silica magma- mafic
–
Basalt
• Pahoehoe
•
Aa
•
Gently sloping flanks- between 2 and 10 degrees
•
Tend to be very large
•
Spatter Cone- minor feature
VOLCANOES
•
Volcanoes are cone-shaped
•
Vent
•
Crater
•
Flank eruption
•
Caldera
• Types:
–
Cinder Cone, Shield, Composite
COMPOSITE VOLCANO
•
Alternating pyroclastic layers & lava flows
• Slopes intermediate in steepness
•
Intermittent eruptions over long time span
• Mostly Andesite
•
Distribution
–
Circum-Pacific Belt (“Ring of Fire”)
–
Mediterranean Belt
COMPOSITE VOLCANO
•
Alternating pyroclastic layers & lava flows
• Slopes intermediate in steepness
•
Intermittent eruptions over long time span
• Mostly Andesite
•
Distribution
–
Circum-Pacific Belt (“Ring of Fire”)
–
Mediterranean Belt
VOLCANIC DOMES
•
Forms above a volcanic vent
•
Viscous lava
–
Usually silica-rich (or cooler magma)
•
Associated with violent eruptions
•
AA
– rubbly surface, broken, jagged
•
Pahoehoe
– ropy surface
Lava Flows
LAVA FLOODS
•
Mafic lava- solidifies to basalt
•
Fissure flows
–
Plateau basalts
•
Columnar structure or jointing
SUBMARINE ERUPTIONS
•
Pillow basalt
