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Chapter 5 : Rocks from molten liquidsRocks from molten liquids
Including adaptions from Dupre and Copeland (2004)
Concepts you should know for the exam
• Texture – grain size of intrusive (e.g., granite) and extrusive rocks (e.g., basalt)
• Relative cooling rates of intrusive and extrusive igneous rocks• Rocks from lavas vs. pyroclastic rocks• Mafic, intermediate and felsic rocks• Know table! (Temperature, Silica, Na, K, Fe, Mg, Ca content)• Melting point as a function of pressure, water content and
composition• Partial melting of magma-generating rocks• Fractional crystallization• Shapes of magmatic bodies – sills, dykes, batholiths• Hot spots and volcanoes (mafic composition)• Volcanoes at convergent margins ( mafic to felsic composition)• Volcanoes at divergent margins (mafic composition)• Lavas, welded tuff, vesicular basalt, volcanic bombs, pyroclastic
flows, volcanic cloud• Relation between the shape of volcano, chemistry, viscosity of
lavas (shield volcano, cinder cone volcano,composite volcano)• Dangerous pyroclastic flows cause almost 30% fatalities natural
disasters vs. tsunamis (~20%)
Lecture OutlineLecture Outline
1.1. Where do magmas form?Where do magmas form?
2.2.How do igneous rocks differ from one How do igneous rocks differ from one
another?another?
3. How do magmas form?3. How do magmas form?
4. Magmatic differentiation4. Magmatic differentiation
5. Forms of magmatic intrusion5. Forms of magmatic intrusion
6. Igneous activity and plate tectonics6. Igneous activity and plate tectonics
Lecture OutlineLecture Outline
1.1. Where do magmas form?Where do magmas form?
2.2.How do igneous rocks differ from one How do igneous rocks differ from one
another?another?
3. How do magmas form?3. How do magmas form?
4. Magmatic differentiation4. Magmatic differentiation
5. Forms of magmatic intrusion5. Forms of magmatic intrusion
6. Igneous activity and plate tectonics6. Igneous activity and plate tectonics
Divergent Plate BoundaryUsually start within continents—grows to become ocean basin
2. How do igneous rocks differ How do igneous rocks differ
from one another?from one another?
Texture – size of crystalsTexture – size of crystals
Coarse-grained rocksCoarse-grained rocks
Fine-grained rocksFine-grained rocks
Mixed texture rocksMixed texture rocks
1. How do igneous rocks differ How do igneous rocks differ
from one another?from one another?
Texture is related to rate of cooling.Texture is related to rate of cooling.
Intrusive igneous rocksIntrusive igneous rocks
Extrusive igneous rocksExtrusive igneous rocks
Andesite - granite near the surface
Hand sample-Santiago de Chile
Microscope slide
Giant’s Causeway, Giant’s Causeway, IrelandIreland
At which plate boundary does water-aided melting help
generate magma?
1. Divergent?2. Transform3. Convergent?
Genetic Classification of Igneous Rocks
• IntrusiveIntrusive: crystallized from slowly cooling magma intruded within the Earth’s crust; e.g. granite, gabbro
Genetic Classification of Igneous Rocks
• ExtrusiveExtrusive: crystallized from rapidly cooling magma extruded on the surface of the Earth as lava or erupted as pyroclastic material.
Extrusive Igneous Rocks Include:
• rocks formed from the cooling of lavaslavas
• rocks formed by the cooling of pyroclasticpyroclastic material, i.e. fragmented pieces of magma and material erupted into the air
Last Days of Pompeii-Karl Briullov--Copyright © 1999. George Mitrevski.
Auburn University
Mt St Helens crater 08-7-80, 60 mph, 800 deg F-pyroclastic flow- USGS
Composition and Classification of Igneous Rocks
• Chemistry: e.g. % SiO2
• Mineralogy: e.g.– Felsic (Feldspar and Silica)– Intermediate– Mafic (Magnesium and Ferric)– Ultramafic
Two basic compositional groups:Two basic compositional groups:
Felsic igneous rocksFelsic igneous rocks
Mafic igneous rocksMafic igneous rocks
Why last figure is so important
• The color and mineral distribution indicate an increasing density and melting temperature. Darker igneous rocks generally weigh more and are formed at higher temperatures and pressures. This reflects the density-stratification of the whole Earth!
Felsic Igneous Rocks: -Igneous rocks rich in minerals
high in silica. They include:
Granite Granite
RhyoliteRhyolite
Intermediate Igneous Rocks:
-Igneous rocks in between in composition between felsic and
mafic igneous rocks. They include:
DioriteDioriteAndesiteAndesite
Mafic Igneous rocks -very low silica content, and consist
primarily of mafic minerals. The most common ultramafic rock is:
PeridotitePeridotite
What controls the melting temperatures of minerals?
*External pressurepressure*and Water content
*Internal compositioncomposition (including internal water content)
Factors Affecting Melting of Minerals (and Rocks)
• PressurePressure: Increased Pressures raises melting points
• Water Content (internal and Water Content (internal and external to the mineral)external to the mineral): Increased Water Content lowers melting points
• CompositionComposition: Felsic minerals melt at lower temperatures than mafic minerals
Lecture OutlineLecture Outline
1.1. Where do magmas form?Where do magmas form?
2.2.How do igneous rocks differ from one How do igneous rocks differ from one
another?another?
3. How do magmas form?3. How do magmas form?
4. Magmatic differentiation4. Magmatic differentiation
5. Forms of magmatic intrusion5. Forms of magmatic intrusion
6. Igneous activity and plate tectonics6. Igneous activity and plate tectonics
4. How do magmas form?
When rocks melt (or partially melt).
Why do rocks melt?Why do rocks melt?
When the temperature exceeds the melting pointmelting point of the rock or some
minerals within the rock.
Partial Melting
--Occurs when some of the minerals forming a rock melt at lower temperatures than other minerals within the same rock
If different minerals melt at different minerals melt at
different pressuresdifferent pressures that means that different minerals become
solid at different temperatures too. What does this imply about the internal composition of a internal composition of a
magma body as it coolsmagma body as it cools??????
Which rocks are hardest to melt?
1. Granite countertop
2. Hawaiian beach sands?
3. marble
Fractional Fractional CrystallizatioCrystallization!n!
Lecture OutlineLecture Outline
1.1. Where do magmas form?Where do magmas form?
2.2.How do igneous rocks differ from one How do igneous rocks differ from one
another?another?
3. How do magmas form?3. How do magmas form?
4. Magmatic differentiation4. Magmatic differentiation
5. Forms of magmatic intrusion5. Forms of magmatic intrusion
6. Igneous activity and plate tectonics6. Igneous activity and plate tectonics
What is Magmatic Differentiation ?
If, during fractional crystallization, the remaining magma were to erupt it would be
(a) more felsic or
(b) more mafic than the original magma????
Lecture OutlineLecture Outline
1.1. Where do magmas form?Where do magmas form?
2.2.How do igneous rocks differ from one How do igneous rocks differ from one
another?another?
3. How do magmas form?3. How do magmas form?
4. Magmatic differentiation4. Magmatic differentiation
5. Forms of magmatic intrusion5. Forms of magmatic intrusion
6. Igneous activity and plate tectonics6. Igneous activity and plate tectonics
What do we know about the shapeshape of magmatic
bodies? Are they sheets? Blobs? Spheres?
“Magmatic Pipes -101”
• Dykes are near-vertical• Sills are horizontal and squeeze in
between other layers of rock• Plutons are deep (km) bodies of
solidified magma. An example of a plutonic rock is granite or gabbro.
www.jemmoore.com/flying/ shiprock.html
Shiprock, NM. It's hard to tell, mainly because I was flying at about 12,000ft when I took this picture, but this massive piece of rock sticks up over 2,000ft from the surrounding plain, and is as big as a small city. It is on Navajo land, and is a significant spiritual site for the Navajo. The hard, volcanic spines radiating out from the main spire are really amazing. From this high up, you couldn't even see an eighteen-wheeler on the ground next to Shiprock, it would be just a speck.
Shiprock, NM• www.jemmoore.com/flying/ shiprock.html• “Shiprock, NM. It's hard to tell, mainly because I
was flying at about 12,000ft when I took this picture, but this massive piece of rock sticks up over 2,000ft from the surrounding plain, and is as big as a small city. It is on Navajo land, and is a significant spiritual site for the Navajo. The hard, volcanic spines radiating out from the main spire are really amazing. From this high up, you couldn't even see an eighteen-wheeler on the ground next to Shiprock, it would be just a speck.”
6. Igneous activity and plate tectonics
Magmatic geosystems:Magmatic geosystems:
Island arc plate subductionIsland arc plate subduction
Plate divergencePlate divergence
Hot-spot volcanismHot-spot volcanism
Continental plate subductionContinental plate subduction
Geomagmatic systems of EarthGeomagmatic systems of Earth
Geomagmatic systems of EarthGeomagmatic systems of Earth
ISLAND ARCPLATE SUBDUCTION
Mafic to intermediateintrusives (plutonism)Mafic to intermediateextrusives (volcanism)Island arc
volcano
Subduction zone
OceaniclithosphereOceaniclithosphere
Island arc plate subductionIsland arc plate subduction
PLATEDIVERGENCE
Basaltic extrusivesBasaltic intrusives
Mid-ocean ridge
Partial meltingOf upper mantlePartial melting
Of upper mantle
Rising magmaRising magma
Plate divergent boundaryPlate divergent boundary
HOT-SPOTVOLCANISM
Basaltic extrusivesBasaltic intrusives
Hot-spot volcano
Mantle plume(hot spot)Mantle plume(hot spot)
MantleMantle
Hot-spot Hot-spot volcanismvolcanism
CONTINENTALPLATE SUBDUCTION
Mafic to felsic intrusivesMafic to felsic extrusives
Subductionzone
Continentalmargin volcano
Oceanic
lithosphere
Oceanic
lithosphere
Continental mantle
lithosphere
Continental mantle
lithosphere
Continental crust
Continental crustOceaniccrustOceaniccrust
Continental Continental plate subductionplate subduction
Summary of Volcanoes
• Subduction volcanoes in continental crustal and oceanic crust at convergent plate margins
• Hot spot volcanoes (anywhere)
• decompression volcanoes at divergent plate margins
END of CHAPTER 5
IGNEOUS ROCKS-rocks from liquid melts