1. Warm Up 11/21 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.
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.
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.

2. Plate Tectonics and Igneous Activity
Chapter 10, Section 3

3. Location of Major Volcanoes

4. 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 ~ km, and melting begins.
The magma will then migrate to form either volcanic island arcs (Aleutians) or continental volcanic arcs (Andes and Cascades)

5. Convergent Plate Boundaries

6. History of Cascade Range Volcanism

7. 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)

8. Divergent Plate Boundaries

9. 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

10. Intraplate Igneous Activity

11. Three Zones of Volcanism

12. Assignment Read Chapter 10, Section 3 (pg. 293-295)
Do Chapter 10 Assessment #1-34 (pg )
For Section 3: Do #’s 10, 12-14, 18, & 25
Study for Chapter 10 Quiz!