GEOL 11: PRINCIPLES OF GEOLOGY 2nd Year
1st Sem
LESSON 7: Igneous Rocks and Processes S.Y 2023 - 2024
Magma Magma Types
-Molten rock beneath the Earth’s surface
-Temperature: ~600-1200 C Mag SiO2 Temp Relati Relati Gas
-Consists of varying amounts of: ma conte range ve ve conte
● Liquids: Ions of Si, O, Al, K, Ca, Na, Fe, Mg nt Densi Visco nt
(Rock forming elements) ty sity
● Solids: minerals, rock fragments
Ultra <45% >1200 High Low Low
● Dissolved gasses: H2O, CO2, SO2 mafic
How are Magmas Generated? Mafic 45-52 1000- Low High High
% 1200
-Melting of upper mantle or lower crust due to:
1. Increase in Temperature Inter 52-63 800-1 Low High High
-Possible heat sources: medi % 000
● Original heat at the time of Earth’s ate
formation
Felsic >63% 650-8 Low High High
● Radioactive delay
/Acidi (more 00
● Conduction from a nearby body of magma
c than
● Mantle plumes may upwell into the crust ⅔)
● (Mantle Plumes creates) Hot spot
○ Abnormally hot regions where the
mantle rises up through lithosphere Magma Differentiation
(e.g., Hawaii)
2. Decrease in Pressure -Any process that causes magma composition to
-Decompression in partial melting: change
● Reducing the pressure lowers the melting -Processes:
temperature ● Assimilation (addition)
● Melting by (adiabatic) pressure reduction ○ Incorporation of elements from the
● (Found in)Divergent boundary surrounding rock into the magma
○ Rift valleys, Mid-Oceanic ridges ● Magma mixing
-Stage 1: Warping of the lithosphere (Beginning of ○ Two or more magmas with
the formation of the divergent plate boundary different compositions are mixed
-Stage 2: Formation of a rift valley together
● East African Rift Valley is at this stage ■ Pinatubo eruption
-Stage 3: Formation of a linear or narrow sea ● Partial melting
● Red sea is at this stage ○ Rocks melt incrementally because
-Stage 4: Formation of Ocean the minerals that compose have
● A well developed mid-oceanic ridge different melting points
● Active crust formation ● Fractional Crystallization
● All major oceans are at this stage ○ The process of crystallizing and
3. Addition of Volatiles removal of crystals from magma
-Flux Melting:
● Lowering melting temperature from
addition of H2O or CO2
● (Found in) Convergent boundaries
● (Found in) Subduction zones - crust and
sediment dehydration of slab
, GEOL 11: PRINCIPLES OF GEOLOGY 2nd Year
1st Sem
LESSON 7: Igneous Rocks and Processes S.Y 2023 - 2024
● Sill
○ Cuts rock horizontally
1. Green = olivine; Gray = Liquid
2. Pyroxene amphiboles
3. Plagioclase
4. Crystallized minerals
Bowen’s Reaction Series
● Laccolith
○ Hill
-Hot at the start
-Ceases to exist (end of the arrow)
-Pyroxene and Amphibole = Mafic
-One mineral, different ions due to difference in
temperate
● Lopolith
○ Basin
PLUTONIC STRUCTURES
Subvolcanic/Plutonic Structures
1. Hypabyssal (Shallow) structures
● Dike
○ Cuts rock vertically
2. Deep-seated structures / Plutons
● Plutons
○ Stock
○ Fingers
1st Sem
LESSON 7: Igneous Rocks and Processes S.Y 2023 - 2024
Magma Magma Types
-Molten rock beneath the Earth’s surface
-Temperature: ~600-1200 C Mag SiO2 Temp Relati Relati Gas
-Consists of varying amounts of: ma conte range ve ve conte
● Liquids: Ions of Si, O, Al, K, Ca, Na, Fe, Mg nt Densi Visco nt
(Rock forming elements) ty sity
● Solids: minerals, rock fragments
Ultra <45% >1200 High Low Low
● Dissolved gasses: H2O, CO2, SO2 mafic
How are Magmas Generated? Mafic 45-52 1000- Low High High
% 1200
-Melting of upper mantle or lower crust due to:
1. Increase in Temperature Inter 52-63 800-1 Low High High
-Possible heat sources: medi % 000
● Original heat at the time of Earth’s ate
formation
Felsic >63% 650-8 Low High High
● Radioactive delay
/Acidi (more 00
● Conduction from a nearby body of magma
c than
● Mantle plumes may upwell into the crust ⅔)
● (Mantle Plumes creates) Hot spot
○ Abnormally hot regions where the
mantle rises up through lithosphere Magma Differentiation
(e.g., Hawaii)
2. Decrease in Pressure -Any process that causes magma composition to
-Decompression in partial melting: change
● Reducing the pressure lowers the melting -Processes:
temperature ● Assimilation (addition)
● Melting by (adiabatic) pressure reduction ○ Incorporation of elements from the
● (Found in)Divergent boundary surrounding rock into the magma
○ Rift valleys, Mid-Oceanic ridges ● Magma mixing
-Stage 1: Warping of the lithosphere (Beginning of ○ Two or more magmas with
the formation of the divergent plate boundary different compositions are mixed
-Stage 2: Formation of a rift valley together
● East African Rift Valley is at this stage ■ Pinatubo eruption
-Stage 3: Formation of a linear or narrow sea ● Partial melting
● Red sea is at this stage ○ Rocks melt incrementally because
-Stage 4: Formation of Ocean the minerals that compose have
● A well developed mid-oceanic ridge different melting points
● Active crust formation ● Fractional Crystallization
● All major oceans are at this stage ○ The process of crystallizing and
3. Addition of Volatiles removal of crystals from magma
-Flux Melting:
● Lowering melting temperature from
addition of H2O or CO2
● (Found in) Convergent boundaries
● (Found in) Subduction zones - crust and
sediment dehydration of slab
, GEOL 11: PRINCIPLES OF GEOLOGY 2nd Year
1st Sem
LESSON 7: Igneous Rocks and Processes S.Y 2023 - 2024
● Sill
○ Cuts rock horizontally
1. Green = olivine; Gray = Liquid
2. Pyroxene amphiboles
3. Plagioclase
4. Crystallized minerals
Bowen’s Reaction Series
● Laccolith
○ Hill
-Hot at the start
-Ceases to exist (end of the arrow)
-Pyroxene and Amphibole = Mafic
-One mineral, different ions due to difference in
temperate
● Lopolith
○ Basin
PLUTONIC STRUCTURES
Subvolcanic/Plutonic Structures
1. Hypabyssal (Shallow) structures
● Dike
○ Cuts rock vertically
2. Deep-seated structures / Plutons
● Plutons
○ Stock
○ Fingers
