Lecture 4

Igneous Rocks, Intrusive Activityand

the Origin of Igneous Rocks

Lecture OutlineI Rock TypesII DefinitionsIII Igneous Rocks

A) Extrusive v IntrusiveB) Textures

i. Intrusive Texturesii. Extrusive Texturesiii. Porphyritic Texture

C) CompositionIV Magma

A) Chemistryi. Felsicii. Intermediateiii. Maficiv. Ultramafic

B) Formation of MagmaC) Magmatic Variability

i. Bowen's Reaction Seriesii. Fractionation

V Plate Tectonics and Igneous RocksA) Divergent BoundaryB) Convergent BoundaryC) Hot Spot

VI Intrusive Bodies

Physical Geology

Rock Types

What is the basis for this classification?

Physical Geology

Definitions

magma - molten rock that is produced from pre-existing rock in the asthenosphere by Earth's internal heat. The magma then rises into the lithosphere and cools on the surface or in the subsurface.

lava - magma flowing on the surface of the Earth

igneous- formed from fire

plutonic - formed at depth

Physical Geology

Igneous RocksPhysical Geology

Igneous Rocks

Intrusive Rocks Extrusive Rocks

Physical Geology

Igneous RocksIntrusive Textures

PhaneriticPegmatitic

Physical Geology

Igneous RocksExtrusive Textures

Aphanitic Glassy

Vesicular

Fragmental

Physical Geology

Igneous RocksPorphyritic Texture

Physical Geology

Igneous RocksComposition

Major Elements

Oxide % by WeightSiO2 35.0-80.0

Al2O3 8.0-22.0

TiO2

Fe2O3

FeO 4.0-MnO 30.0MgOCaONa2O 1.5-8.0

K2O 0.5-8.0

H2O+,- varies

P2O5 <0.15

CO2 varies

}Minor (Trace) ElementsLi, Be, Sc, V, Cr, Co, Ni, Cu, ZnGa,Rb, Sr, Y, Zr, Nb, Ba, Pb, F, Cl, S

Rare Earth Elements

Physical Geology

MagmaPhysical Geology

Felsic Magma

silica content - high, >65% temperature - < 9000Cviscosity - highNa, K, Al content - highCa, Fe, Mg content - very loweruption - explosive (Mount St. Helens)minerals - Na-rich plagioclase feldspar

potassium feldsparquartz

Physical Geology

Intermediate Magma

silica content - intermediate, 53 - 65%temperature - 900 - 11000Cviscosity - intermediateNa, K, Al content - intermediateCa, Fe, Mg content - intermediateeruption - intermediate (Andes Mtns.)minerals - plagioclase feldspar

amphibole

Physical Geology

Mafic Magma

silica content - low, 45 - 52% temperature - 1100 - 13000Cviscosity - low (fluid)Na, K, Al content - lowCa, Fe, Mg content - higheruption - quiet (Kilauea)minerals - Ca-rich plagioclase feldspar

pyroxeneolivine

Physical Geology

Ultramafic Magma

silica content - very low, <45% temperature - ~14000Cviscosity - very low (fluid)Na, K, Al content - very lowCa, Fe, Mg content - very higheruption - none (Cyprus)minerals - pyroxene

olivine

Physical Geology

Igneous RocksMagma Formation Processes

Decompression Melting

Addition of Impurities

Temperature (Geothermal Gradient)

Physical Geology

Magma FormationThe Geothermal Gradient

Physical Geology

Magma FormationImpurities

Physical Geology

Magmatic VariabilityBowen's Reaction Series

Physical Geology

Magmatic VariabilityFractionation

Differentiation/Partial Melting

Assimilation

Mixing

Physical GeologyPhysical Geology

Magmatic VariabilityDifferentiation

Physical Geology

Magmatic VariabilityAssimilation

Physical Geology

Magmatic VariabilityMagma Mixing

Physical Geology

Plate Tectonics and Igneous RocksPhysical Geology

Plate Tectonics and Igneous RocksDivergent Boundary

Physical Geology

Plate Tectonics and Igneous RocksConvergent Boundary

Physical Geology

Plate Tectonics and Igneous RocksHot Spots

Physical Geology

Intrusive BodiesPhysical Geology

Shallow Intrusive Bodies

Volcanic Neck

Ship Rock, NM

Physical Geology

Shallow Intrusive Bodies

Sill

Dike

Physical Geology

Deep Intrusive Bodies

Batholith

Stock

Diapir

Physical GeologyPhysical Geology