IGNEOUS PROCESSES

Question 1

• Describe the rock cycle, the driving forces, and basic formation of each rock type

Answer 1

o Rocks- consolidates mixtures of mineral
o Igneous
 Formed from crystallization of magma
o Sedimentary
 Formed from weathered fragments of other rocks
 Fragments are buried, compresses and consolidates
o Metamorphic
 Formed by temp, pressure, fluids and time
o The rock cycle
 Can start anywhere and any rock can transform into another, except sedimentary rocks don’t transform into igneous because they have to become metamorphic first

Question 2

o Lava

Answer 2

 Molten rock above the ground

Question 3

magma

Answer 3

Molten rock below the ground
 Types
* Crystal (solid)
* Melt (liquid)
* Volatiles (gas)
 Dominated by silicon and oxygen
* The more silicon the more felsic

Question 4

• Differentiate extrusive and intrusive igneous rocks

Answer 4

o Intrusive plutonic-magma slowly cools below the surface
 Large crystals
o Extrusive/ volcanic- magma cools quickly above the surface
 Small/no crystals

Question 5

o Partial melting

Answer 5

 All magmas are derived from partial melting of rock in the mantle or crust
 Rocks are made form different minerals
 Minerals melt at different temps
 Temps rarely exceed that of all mineral’s melting point
 This result in only part of rock melting

Question 6

o Ways to make magma

Answer 6

 Increase temp
 Decrease pressure (decompression melting)
* Decrease pressure while maintaining temp
* At divergent boundaries mantle rock rises in response to the newly created space
* The mantle rocks rise and are kept at approx same temp, but reduce pressure, inducing melting
* Hot spots (mantle plume) are deep magmas from deep within the mantle
* As the plume rises it continues melting due to decreases in pressure
 Add water or other volatiles (flux melting)
* Adding volatiles lowers the melting point of rocks
* Liquidus curve shifts left
* At convergent boundaries where subduction occurs water is released into he mantle from the subducting slab
* The added water (volaties) lower the melting point of the mantle rock

Question 7

Tectonic summary for melting

Answer 7

 Most melting is controlled by plate tectonics

Question 8

• Know the broad classification of chemical compositions of magma

Answer 8

mafic - 50 % Sio2, least Na2O, most Al2O3, most FeO
felsic- 75% Sio2, most in Al2O3
intermediate- 55% SiO2

Question 9

• Explain how magma and rock composition is influences by partial melting and fractional crystallization

Answer 9

crystallization of magma, the sequence of crystallization: Bowen’s reaction series
fractional crystallization

Question 10

o Crystallization of magma

Answer 10

 Rock crystalizes at different temps depending on mineral composition
 Minerals crystalize at different temps

Question 11

o The sequence of crystallization: Bowen’s reaction series

Answer 11

 More mafic crystalize first
 Plagioclase crystallizes around the same temp as procxene but depends on the plagioclase composition
* Ca rich (Anorthite) Na rich (Albite)  K rich (K-spar

Question 12

o Fractional crystallization

Answer 12

 The consequence of bownes Rxn series is that as magmas cool, mafic minerals crystalize first, making the magma composition more felsic

Question 13

• Differentiate dikes and sills

Answer 13

o Depending on how tabular bodies of magma interact with surface statigraphy, they are either dikes or sills

Question 14

sill

Answer 14

 Concordant (parallel) with existing laying

Question 15

dike

Answer 15

 If there is no layer present

Question 16

• Identify plutons based on morphology and relation to surrounding rocks

Answer 16

o Any body of magma that crystalizes underground is a pluton
o They can be divided by shape and size
 Stocks/ batholiths
* Large pluton (>100km2) usually formed by several stocks merging together
 Sills
 Fyke
 Laccolith
* Mushroom shaped body of magma that inflates between layers, moving them upwards
 Volcanic pipe

Question 17

o Texture of rocks is a result of the crystallization process or the eruptive style of the volcano

Answer 17

 Glassy
 Porphyritic texture
* Two distinctly different crystal sizes
 Phaneritic (coarse-grained) texture
* Large mineral grains
 Vesicular texture (pumice)
* Extrusive rock containing voids by gas bibbles
 Pyroclastic (fragmental) texture
* Produced by the consolidation of fragments (ash, once molten blobs or large angular blaocks) that were ejected by volcdanic eruption
 Aphanitic (fine grained) texture

Question 18

• Classify igneous rocks using basic terms to describe composition and texture

Answer 18

o Porphyritic texture
 After minerals crystalize in the magma, and are brought up to the surface, the lava will quench and from a porphyritic texture
o The more mafic the rock the higher portion of ferromagnesian minerals it contains