Igneous Rocks and Intrusive Igneous Activity - The Changing Earth: Exploring Geology and Evolution - page 84

OUTLINE
Introduction
The Properties and Behavior of Magma and Lava
How Does Magma Originate and Change?
Igneous Rocks—Their Characteristics and Classifi cation
Intrusive Igneous Bodies—Plutons
How Are Batholiths Intruded into Earth's Crust?
GEO-INSIGHT: Plutons
GEO-FOCUS: Some Remarkable Volcanic Necks
Geo-Recap

OBJECTIVES
At the end of this chapter, you will have learned that
With few exceptions, magma is composed of silicon and
oxygen with lesser amounts of several other chemical elements.
Temperature and composition are the most important controls
on the mobility of magma and lava.
Most magma originates within Earth's upper mantle or lower
crust at or near divergent and convergent plate boundaries.
Several processes bring about chemical changes in magma, so
magma may evolve from one kind into another.
All igneous rocks form when magma or lava cools and crystal-
lizes, or by the consolidation of pyroclastic materials ejected
during explosive eruptions.
Geologists use texture and composition to classify igneous
rocks.
Intrusive igneous bodies called plutons form when magma
cools below Earth's surface. The origin of the largest plutons is
not fully understood.

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View of the Sierra Nevada taken west of Lone Pine, California. The rocks in
this view are part of the Sierra Nevada batholith, a huge mass of granite
and related rocks made up of many intrusive bodies. The high peak toward
the right is Mount Whitney, which at 4421 m is the highest peak in the
continental United States.

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