Transcript 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.
–
Porphyritic 2 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
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Mostly feldspar & quartz
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Light-colored Basalt (& Gabbro)
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“Low” in Si + O
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High in Fe + Mg
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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 underground Plutons Volcanic neck- shallow intrusion Fills cracks (joints)- tabular bodies – DIKE • If no layering in
country rock
• If country rock is layered Discordant – SILL- less common • Concordant parallel 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 layered Discordant – 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 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 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 2 S, HCl Gases & pyroclastics – 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) – Glassy-
Obsidian
– 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