Lesson 5: Magma Generation and Igneous Rocks Flashcards
Igneous rocks form when:
a melt solidifies at or below the Earth’s surface
The molten rock beneath the Earth’s surface is called ____.
Magma
The greatest amount of magma is created at
Divergent plate boundaries
How is magma generated at subduction zones?
Addition of volatiles
What type of magma contains the lowest amount of silica?
a. Felsic
b. Intermediate
c. Mafic
d. All magmas contain the same amount of silica
c. Mafic
_______ is a mafic extrusive igneous rock.
Basalt
A _________ is a concordant igneous rock body which runs parallel to pre-existing bedrock.
Sill
Magma rises toward the Earth’s surface because:
it is less dense than the surrounding rocks
Why are intrusive igneous rocks from a batholith generally coarser-grained than those from volcanic vents?
They cooled more slowly and thus had more time to grow
A _______ texture indicates two stages of cooling.
Porphyritic
Magma
molten/partially molten material found beneath the surface of the Earth
Lava
What we call magma that reaches the Earth’s surface.
Where does magma form in terms of plate tectonics?
Mostly at divergent plate boundaries
- mid-ocean ridges
- Continental rifts
Few at convergent plate boundaries
- subduction zones
What are the three ways to generate magma
- Decompression melting
- Addition of volatiles
- Addition of heat
What is decompression melting?
a rapid decrease in pressure that can cause the mantle to melt without an increase in temperature.
Where do we see decompression melting in terms of plate tectonics?
Divergent plate boundaries