Transcript Plate Tectonics and Igneous Activity

Warm Up 12/3
Which of the following is NOT true about a batholith?
a. It is considered a pluton.
b. It may form the core of a mountain range.
c. It is often a small part of a sill.
d. It is the largest intrusive igneous body.
2) What is true about all plutons?
a. They form near Earth’s surface.
b. They form above Earth’s surface.
c. They form below Earth’s surface.
d. They cut across other rock layers.
3) Which of the following factors affects the melting point
of rock?
a. water content
c. composition of the material
b. confining pressure
d. all of the above
Answers: 1) c. 2) c. 3) d.
1)
Plate Tectonics and
Igneous Activity
Chapter 10, Section 3
Location of Major Volcanoes
Convergent Plate Boundaries
The basic connection between plate
tectonics and volcanism is that plate
motions provide the mechanisms by which
mantle rocks melt to generate magma
 When an oceanic plate sinks under
another plate, it brings water and rock
along with it. When that plate reaches a
depth of ~100-150 km, and melting
begins.
 The magma will then migrate to form
either volcanic island arcs (Aleutians) or
continental volcanic arcs (Andes and
Cascades)

Convergent Plate Boundaries
History of Cascade Range
Volcanism
Divergent Plate Boundaries
Most magma is produced during seafloor
spreading (at the ocean ridges)
 As the plates move apart, rock from the
mantle rises to fill the gap
 As this rock rises, the confining pressure
decreases, causing it to melt and form
basaltic magma
 This basaltic magma is less dense than the
solid mantle rock, so it rises faster
 Most spreading ridges are located along the
axis of an oceanic ridge (not the East African
Rift)

Divergent Plate Boundaries
Intraplate Igneous Activity
Intraplate Volcanism – occurs within a
plate, not at a plate boundary (Hawaii and
Yellowstone)
 Most intraplate volcanism occurs where a
mass of hotter than normal mantle material
called a mantle plume rises toward the
surface
 Most plumes are thought to begin at the
core-mantle boundary
 As the hotter mantle rock rises, it melts the
rock around it, causing magma to form
 It appears on the surface as a hot spot, and
more than 40 of these have been identified

Intraplate Igneous Activity
Three Zones of Volcanism
Assignment
 Read
Chapter 10, Section 3
(pg. 293-295)
 Do Section 10.3 Assessment #1-6
(pg. 295)
 Study for Chapter 10 Quiz!