Igneous Rocks - outline

IGNEOUS ROCKS (Chapter 4) - Outline

Last updated: 02/01/07

Generalizations about igneous rocks

1. How do igneous rocks differ from one another?

Classification criteria

grain or fragment size

amounts (modes) of minerals

rock chemistry

Texture

interpretation of origin

extrusive rocks

intrusive rocks

Compositional groupings

silica, Mg-Fe, Alkali contents

characteristics of rocks as a function of variation

mineral content

melt temperature

melt viscosity and explosivity

extrusive vs. intrusive rock type equivalents

2. How do magmas form?

	Variations in temperature of melting
	Separation of melts from source
	Magma chambers
	Melt buoyancy

3. Where do magmas form?

Sufficiently deep in the Earth

relation to geothermal gradient

Places of locally elevated temperature

4. Magmatic differentiation

Crystallization sequences

Bowen's reaction series

Differentiation process

Palisades Sill example

Magma mixing

5. Forms of magmatic intrusion

Discordant intrusions

	Batholiths
	Stocks
	Dikes
	Veins

Concordant intrusions

Sills

6. Igneous activity and plate tectonics

Divergent boundaries (ridges and rifts)

	Decompression melting
	Cross-sections of ridge system

Hot spots

Convergent subduction zones - island arcs and continental arcs

	Fluid enhanced melting
	Zone of large compositional variations
	region of explosive volcanism

	grain or fragment size
	amounts (modes) of minerals
	rock chemistry