1. Intrusive Igneous Activity

2. Plutons
intrusive igneous structures that result from the cooling/hardening of magma beneath surface.
classified according to shape, size, and relationship to surrounding rock layers

3. Types of Plutons
Dikes
Sills
Batholiths

4. Sills
Horizontal plutons formed when magma is intruded in between sedimentary layers

5. Dikes
intrusive igneous features that cut across preexisting rock layers.
Dikes can form when magma invades fractures in the surrounding rocks.

6. must have a surface exposure greater than 100 km2
Batholiths
large masses of igneous rock that formed when magma at depth, became crystallized, and was exposed by erosion
must have a surface exposure greater than 100 km2

7. Geothermal Gradient
Temp naturally increases with depth but is not sufficient to melt rock in the lower crust and upper mantle

8. Origin of Magma 1. Increase Temperature 2. Reduce Pressure
3. Water (Wet rocks melt easier)

9. Additional heat can be generated by
crustal rocks heating up from friction during subduction

10. Where Do Volcanoes Occur?
Convergent plate boundaries: 75% of active volcanoes
Ex: Ring of Fire
Subduction zone
Divergent plate boundaries: as plates move apart, magma rises to fill the space

11. Do we live by a Volcano?