Download EXTRUSIVE IGNEOUS ROCKS Magma and Lava

Igneous Rock Names
and Compositions
EXTRUSIVE IGNEOUS
ROCKS
Volcanoes and Volcanic Rocks
• Composition • Intrusive
Rock Name
Name
•
•
•
•
Ultramafic
Mafic
Intermediate
Silicic (felsic)
•
•
•
•
Peridotite
Gabbro
Diorite
Granite
• Volcanic
Rock Name
•
•
•
•
(Komatiite)
Basalt
Andesite
Rhyolite
Magma and Lava
• Magma is the term for any molten
silicate material, whether below
the surface or on top.
• Volcanic rocks are erupted on the
surface.
– Volcanic rocks are fine-grained (<1
mm)
• Lava is the term for a magma on
the surface.
Most Volcanoes are at Plate Boundaries
Geologic Settings
1
Basaltic Eruptions
Pahoehoe, Hawaii (Basalt)
• Low Viscosity
• High Temperature (1000 - 1200ºC)
• Normally Quiescent Lava Flows
– Aa - early, low temperature, blocky
flow
– Pahoehoe - later high temperature
ropy flow
– Pillow Lavas - underwater flow
• Edifice
– Shields
– Cinder cones
Aa, Hawaii (Basalt)
Pillow Lava, Kauai (Basalt)
Nyiragongo, Congo (Zaire)
2
Goma, Congo (Zaire)
Cinder
Cone,
Pu’uo’o,
Hawaii
(Basalt)
Basaltic Eruptions
Skjaldbreidur Shield, (Basalt)
Cinder Cone + Caldera, (Basalt)
Most Volcanoes are at Plate Boundaries
• Low Viscosity
• High Temperature (1000 - 1200ºC)
• Normally Quiescent Lava Flows
– Aa - early, low temperature, blocky
flow
– Pahoehoe - later high temperature
ropy flow
– Pillow Lavas - underwater flow
• Edifice
– Shields
– Cinder cones
3
Andesite Eruptions
•
•
•
•
•
Geologic Settings
Higher viscosity (higher polymerization )
Lower temperature
More water, more explosive
Subduction zone volcanism
Flows
– Viscous lava flows
– Pyroclastic flows
• Edifice
– Composite Cones
Andesite Flow, Mt Shasta
Composite Cone, Mt. Fuji
Composite Cone, Mt. Daisen
Composite Cone, Mt. St Helens
4
Andesite Eruptions
•
•
•
•
•
Higher viscosity (higher polymerization )
Lower temperature
More water, more explosive
Subduction zone volcanism
Flows
– Viscous lava flows
– Pyroclastic flows
• Edifice
– Composite Cones
5
Rhyolite Eruptions
• Very high viscosity
• Low temperature (600 - 800ºC)
• Massive Pyroclastic eruptions
– Air fall (pumice)
– Ash Flow (Nuée Ardente) Tuff
– Obsidian Flows
• Edifice
Rhyolite Eruptions
• Associated Phenomena
– Hot Springs
– Geysers
– Fumaroles
• Geologic Setting
– Continental Margins and Interiors
– Subduction Zones
– Caldera (5 - 25 km)
– Resurgent dome
Geologic Settings
Ash-Flow
Tuff
with AirFall Units
Pumice = Glass foam
Ash-Flow Tuff Unit
Non-Welded Top
Welded Core
Vitrophyre
Non-welded base
6
Silicic Tuff Units (Jemez, NM)
Sulfur Fumarole, Nysseros
Obsidian Flow
Non-welded
Air-Fall Units
Caldera with Cinder Cone
Crater Lake, OR
Geyser
Old Faithful
(Yellowstone)
Rhyolite Eruptions
• Very high viscosity
• Low temperature (600 - 800ºC)
• Massive Pyroclastic eruptions
– Air fall (pumice)
– Ash Flow (Nuée Ardente) Tuff
– Obsidian Flows
• Edifice
– Caldera (5 - 25 km)
– Resurgent dome
7
•
•
•
•
•
Andesite Eruptions
Basaltic Eruptions
Higher viscosity (higher polymerization )
Lower temperature
More water, more explosive
Subduction zone volcanism
Flows
• Low Viscosity
• High Temperature (1000 - 1200ºC)
• Normally Quiescent Lava Flows
– Aa - early, low temperature, blocky
flow
– Pahoehoe - later high temperature
ropy flow
– Pillow Lavas - underwater flow
• Edifice
– Shields
– Cinder cones
– Viscous lava flows
– Pyroclastic flows
• Edifice
– Composite Cones
Geologic Settings
Most Volcanoes are at Plate Boundaries
8