Answer the following questions concerning Figure 2.

1. What type of basalt occurs at point "X"?

2. What type of basalt occurs at point "Y"?

3. Do these basalts differ in chemical composition?

4. If so, what are the major differences? (3 pts.)

5. If so, why do they differ? (3 pts.)

1. The line of seamounts noted in question #10 under "Tectonic Evolution of the South Atlantic" above probably consist of what type of basalt? (2 pts.)

2. Does this basalt differ from that found on Tristan da Cunha? (2 pts.)

3. How do these basalts differ geochemically from that which would be dredged from the rift valley anywhere along the MOR in the South Atlantic? Be specific. (5 pts.)

4. Where in the South Atlantic might you find basalt similar in composition to that found today on Iceland? (1 pt.)

Answer & do the following:

1. How deep into the ocean crust have the DSDP & ODP drilled? Sketch the crustal structure encountered by drilling? (5 pts.)

2. Where have deep diving submersibles made investigations of the MOR rift valley volcanism & what types of rift valley volcanic activity have been deduced from submersible studies? (5 pts.)

3. How do deep diving submersible & drilling results relate & how do they combine to give a coherent picture of volcanic processes in MOR rift valleys? (5 pts.)

Draw a cross-section through oceanic crust showing its structure. Label each crustal layer and the mantle and indicate seismic velocity, lithology, and significant fabrics for each layer.

Briefly summarize the distribution of Layers 2A, 2B, and 2C in the upper oceanic crust as a function of age, and explain the reason for this distribution.

Briefly summarize the petrologic data discussed in class which indicates that the parent magmas from which tholeiitic and alkalic basalts are derived form at different depths in the mantle.

Briefly summarize the geochemical data discussed in class which indicates that there are multiple mantle sources for basalt melts. Why is 87Sr/86Sr so useful?

A. Matching - Match the given items in the left column with the most appropriate item in the right column. Place the letter for the right hand column item in the blank provided to the left of the number.

____1. Layer 2A a. ~8 km/sec seismic velocity

____2. Layer 2C b. thins away from ridge crests

____3. Layer 3 c. increase in velocity from ~7 km/sec to ~8km/sec

____4. MOHO d. sheeted dikes

____5. Mantle e. gabbro

____1. Layer 2A a. sheeted dikes

____2. Layer 2C b. crust/mantle boundary

____3. Layer 3B c. ultramafic rocks

____4. Mantle d. unmetamorphosed gabbro

____5. MOHO e. porous pillow lavas