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Volcanoes (Geology 115) – Exam #1 Review

Lecture 5 – Magma Generation

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Exam #1 will cover all materials from weeks 1 – 6. Exam topics will be from lectures 1 – 5. Exam questions will include multiple choice, true/false, matching, and short answer. Below is a list of questions that outline topics that I may test you on. These questions are intended to help you study, but are not intended to be fully encompassing. However, if you can answer these questions, you should be well prepared. Please note that exam questions will be based on lecture material, homework, and in-class assignments.

 

1. What is magma? What is in magma? Be more specific than molten rock beneath the earth’s surface.

a. What is in the silicate liquid?

b. How do we know the outer core is not a source of magma?

c. What controls what minerals will form in a magma? How do we know minerals are in magma?

d. Why is the gas dissolved? What are three most abundant gases that erupt from volcanoes? How do we know gas in magma?

2. Where is magma generated (99% of the time)?

a. How do we know the mantle is completely solid?

b. What is the geothermal gradient?

c. Under normal conditions the mantle is not hot enough to melt. Why?

i. What is the melting curve for peridotite?

ii. Why does the melting curve for peridotite change with depth?

iii. Is the mantle solid below or above the melting curve?

iv. Does the mantle melt above or below the melting curve?

v. Does the mantle ever reach 100% melted?

3. What is partial melting? What is the simplest definition of partial melting?

4. How does the mantle change to start melting? If the conditions have to change in the mantle to trigger melting, what are those initial conditions?

a. What are two mechanisms that cause partial melting?

5. Describe how magma originates at divergent zones of volcanism.

a. What process generates magma at divergent pb?

b. Where does melting occur?

c. What is the composition of the magma that forms from partial melting?

6. Describe how magma originates at convergent zones of volcanism.

a. What process generates magma at convergent zone of volcanism?

b. What is a flux? What is the flux for the mantle?

c. What is the composition of the magma that forms from partial melting?

7. Describe how magma originates at intraplate zones of volcanism.

a. What process generates magma at divergent pb?

b. Where does melting occur?

c. What is the composition of the magma that forms from partial melting?

8. What is partial melting ultimately controlled by?

a. What are the two “rules” of partial melting?

b. How does the composition influence melting? In other words, what mineral composition melts first and why?

9. Mafic minerals:

a. Why do mafic minerals melt last?

b. Look at the mafic minerals on slide 15. Which mafic minerals melt first? Why? What is the composition of the magma that forms from partial melting?

10. Felsic minerals:

a. Why do felsic minerals melt first?

b. What felsic mineral is the exception to this rule?

11. What is the composition of the mantle? What is the rock that makes up the mantle?

12. What is the composition of the magma that forms after melting the mantle? Why?

a. To help address the “why”, be able to answer the following questions presented on slide 18:

i. What rock makes up the mantle? What is composition of peridotite?

ii. What are the two minerals that make up peridotite?

iii. What mineral in peridotite has a lower melting temperature and will melt first?

iv. Is this mineral a mafic or felsic mineral?

v. What is the composition of the magma that forms?

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