The definition of an igneous rock.  

Igneous rock – Made by the freezing of a melt -- Make up all of oceanic crust and much of the continental crust

The difference between magma and lava.  

1.     Magma – Melt that exists below the Earth’s surface

a.     All magmas silicon and oxygen

b.     Because it is a liquid, atoms are grouped in clusters and are free to move with respect to each other

2.     Lava - Melt that has erupted from a volcano at the surface of the Earth

a.     Pyroclastic debris – Some of the debris forms when clots of lava fly into the air in lava fountains and then freeze to form solid chunks before hitting the ground

                                      i.     Ash – Explosion blasts a fine spray of lava that freezes to form fine particles

Where igneous rocks are formed.  

1.     Subduction yields a volcanic arc

a.     The oceanic crust that subducts contains some volatiles.  When the crust sinks into the mantle its volatiles causes the ultramafic rock of the asthenosphere to partially melt and produce a basaltic magma—magma either rises to erupt as lava or undergoes fractional crystallization (becoming intermediate or felsic lava)

2.     Isolated hot spots – isolated volcanoes, independent of plate-boundary interactions

a.     Many hot-spot volcanoes form above plumes of hot mantle rock that rise from the core-mantle boundary

                                      i.     Plume does not consist of magma but when the hot rock of a plume reaches the base of the lithosphere, decompressions causes the rock (peridotite) of the plume to undergo partial melting – generating mafic magma.  The mafic magma then pools in a magma chamber in the crust and eventually erupts

3.     Continental rifts

4.     Mid-ocean ridges

a.     Divergent boundary – as the asthenosphere rise it undergoes decompression which leads to partial melting and basaltic magma

How igneous rocks are classified.

a.     Texture – rate it cooled

                    i.     Coarse-grained (phaneritic) rocks – (cooled slower than fine grained) crystals large enough to be identified with the naked eye

                   ii.     Fine-grained (aphanitic) rocks – (cooled faster than coarse-grained rock) crystals too small to be identified with the naked eye

               iii.     Porphyritic rocks – larger crystals surrounded by mass of fine crystals

1.    Melt cools slowly at depth then the melt erupts and the remainder cools quickly

b.     Composition - Crystalline igneous rocks – based on silica content

                 iv.     Ultramafic

1.     Density: very high

2.     Temperature: Very high (up to 1300 C)

3.     Viscosity: very low

                   v.     Mafic

1.     Density: high

2.     Temperature: high

3.     Viscosity: Low, thin hot runny eruptions

                 vi.     Intermediate

1.     Density: low

2.     Temperature: low

3.     Viscosity: High, Explosive eruptions

                vii.     Felsic

1.     Density: very low

2.     Temperature: Very low (600 to 850 C)

3.     Viscosity: Very high, Explosive eruptions

The names of the six igneous rocks discussed in class.

Mafic

Basalt

Gabbro

Intermediate

Andesite

Diorite

Felsic

Rhyolite

Granite

 Silica, density, viscosity and temperature characteristics of the 6 igneous rocks.  

Mafic (Least silica) (high density) (low viscosity) (high temp)

Basalt

Gabbro

Intermediate (more silica) (less density) (high viscosity) (low temp)

Andesite

Diorite

Felsic (Most silica) (low density) (very high viscosity) (very low temp)

Rhyolite

Granite

basalt blobs that form when magma comes out on the seafloor, cools quickly

The difference between intrusive and extrusive rocks.  

1.     Intrusive igneous rock – Rock made by the freezing of magma underground, after is has pushed its way into preexisting rock of the crust

2.     Extrusive igneous rock – Rock that forms by the freezing of lava above ground after it spills out onto the surface of the Earth

The three ways to melt a rock. 

a.     Decrease in pressure (decompression)

                                      i.     Pressure at great depth prevents atoms from breaking free of solid mineral crystals (pressure prevents melting), therefore a decrease in pressure can permit melting

                                     ii.     Decompression melting – if the pressure affecting hot rock decreases while the temperature stays the same, a magma forms.

1.     Geotherm - temperature of rocks within the earth

2.     Solidus- Temperature where rocks start to melt

3.     Liquidus- Temperature where rocks are completely melted

b.     Change in melting temperatures - addition of volatiles

                                      i.     Magma also forms at locations where chemicals called volatiles (can exist in gaseous forms at the Earths surface) mix with hot mantle rock

                                     ii.     When volatiles mix with hot rock they help break chemical bond and help melt the rock (decrease the rocks melting temperature)

c.      Addition of heat - heat transfer from rising magma

                                      i.     When rock, or magma, from the mantle rises up into the crust it brings heath with it.  This raises the temperature of the surrounding crustal rock and is able to melt some of it.

1.     Geotherm 

2.     Solidus

3.     Liquidus

1.     Geotherm - temperature of rocks within the earth

2.     Solidus- Temperature where rocks start to melt

3.     Liquidus- Temperature where rocks are completely melted

The effect that pressure has on melting temperature.  

i.         Pressure at great depth prevents atoms from breaking free of solid mineral crystals (pressure prevents melting), therefore a decrease in pressure can permit melting

ii.         Decompression melting – if the pressure affecting hot rock decreases while the temperature stays the same, a magma forms.

The effect that water has on the melting temperature.  

a.     Addition of volatiles

                    i.     Magma also forms at locations where chemicals called volatiles (can exist in gaseous forms at the Earths surface) mix with hot mantle rock

                   ii.     When volatiles mix with hot rock they help break chemical bond and help melt the rock (decrease the rocks melting temperature)

The main sources of heat in the Earth.  

1.     Heat left over from the Earth’s early days

a.     The large collisions and mergings created lots of kinetic energy (energy of motions) which transformed into heart energy

2.     Gravity pulling matter inward

a.     Such compression made the Earth’s inside even hotter

3.     Iron began to melt

a.     As the Earth got hot enough, iron began to melt and sink to the center of the earth to form the core.  The friction of the sinking only made it hotter

4.     Large collision

a.     After differentiation a mars-sized object collided with the Earth creating lots of heat

5.     Radioactive elements

a.     The decay of a single radioactive atom produces a tiny amount of heat but the cumulative effect of radioactive decay had slowed the cooling of the planet.

How melting of rocks differs from the melting of ice. 

Ice melts to water at one temperature.   Rocks start melt at the solidus point; at this point there is part magma and also some crystals.  Then there is a liquidus point where the crystals completely melt to magma.  This is because rocks are made of many different types of minerals with different melting points. 

 How melt is formed at spreading centers and subduction zones.  

1.     Subduction yields a volcanic arc

a.     The oceanic crust that subducts contains some volatiles.  When the crust sinks into the mantle its volatiles causes the ultramafic rock of the asthenosphere to partially melt and produce a basaltic magma—magma either rises to erupt as lava or undergoes fractional crystallization (becoming intermediate or felsic lava)

2.     Continental rifts – divergent boundary

3.     Mid-ocean ridges

a.     Divergent boundary – as the asthenosphere rise it undergoes decompression which leads to partial melting and basaltic magma

The definition of decompression melting.  

Decompression melting – if the pressure affecting hot rock decreases while the temperature stays the same, a magma forms.

How mantle peridotite can melt to form basalt. 

-when the hot rock of a plume reaches the base of the lithosphere, decompressions causes the rock (peridotite) of the plume to undergo partial melting – generating mafic magma. 

 Partial melting

1.     Partial melting: Rocks contain a variety of different minerals.  Magma flows out of the original rock long before the rock completely melts.  Therefore, the magma that forms as a rock begins to melt does not have the same composition as the rock it came from.  The magma tends to have more silica.  This is the process that the melt carries away silica.

a.     The solid rock left behind will be more mafic than the original rock (less silica)

b.     Partial melting of ultramafic rock produces mafic magma.  Partial melting of intermediate rock produces a felsic magma

Fractional crystallization

Magma changes composition as it cools because formation and sinking of crystals remove certain atoms from the magma.

 Bowen's reaction series.  

the sequence in which different silicate minerals crystallize during the progressive cooling of a melt[image]

Why magma rises.  

-It is less dense than solid mantle, so it rises. 

When density of magma = density of curst, it stops rising

-The weight of overlying rock creates pressure that squeezes the magma upward.