GLG 101

Chapter 3

Igneous Rocks and Intrusive Igneous Activity

Magma and Lava

magma: molten rock material below surface

lava: magma at Earth surface

Igneous rocks originate from magma or lava

intrusive (plutonic) igneous rocks: form within Earth

extrusive (volcanic) igneous rocks: form on surface of Earth

Composition: with respect to silica

felsic: >65% silica

intermediate: 65-53% silica

mafic: 45-52% silica

ultramafic: <45% silica

Temperature: of formation

mafic: around 1000 to 1200 degrees C

felsic: around 900 degrees C

Viscosity: (resistance to flow)

controlled by silica content

Igneous rocks:

Texture:

aphanitic

phaneritic

porphyritic

pyroclastic (fragmental)

Composition:

felsic

intermediate mafic

ultramafic

Bowen's Reaction Series:

derivation of felsic (intermediate) magmas from mafic magmas

Classification of igneous rocks:

composition texture

Intrusive igneous bodies (plutons):

dikes and sills

laccoliths

volcanic pipes and necks

batholiths and stocks