a) Magma generation and rock types for the convergent oceanic-continental setting:
o In three or four sentences, explain how the first/primary magma is generated in this tectonic setting. (2.5 pts)
o Name the type of rock that is melted(to produce the primary melt) here and also the chemical composition of the magma that is formed. (1 pts)
o What type(s) of lava are eventually erupted at the surface? In a sentence, explain why the chemical composition of the lava is or is not different from the first magma generated in this tectonic setting. (2 pts)
o What are the physical properties of these lavas? (0.5 pt)
o Name one type of volcano that forms in this setting. (0.5 pt)
o Are eruptions here typically effusive or explosive? Why? (1 pts)
b) Magma generation and rock types for the hot spot beneath oceanic lithosphere.
o In three or four sentences, explain how the first/primary magma is generated in this tectonic setting. (2.5 pts)
o Name the type of rock that is melted (to produce the primary melt) here and also the chemical composition of the magma that is formed. (1 pts)
o What type(s) of lava are eventually erupted at the surface? In a sentence, explain why the chemical composition of the lava is or is not different from the first magma generated in this tectonic setting. (2 pts)
o What are the physical properties of these lavas? (0.5 pt)
o Name one type of volcano that forms in this setting. (0.5 pt)
o Are eruptions here typically effusive or explosive? Why? (1 pts)
3.(15 pts) Pictured below is a map view of southern Alaska. The red triangles are volcanoes, darker blues indicate deeper water depths, and the green scale bar is 500 km long.
a. Name the type of plate tectonic setting pictured here. Be as specific as possible. (1 pts)
b. Describe the motion of the lithosphere at this location (1-2 sentences). (1pt)
c. Give the names of the major physiographic features that are associated with this plate tectonic setting, labeled on the map as: (2 pts)
A.
B.
d. Would you expect to experience earthquakes in this plate tectonic setting? Why or why not?Describe the magnitude of these earthquakes, and explain whether or not they would be dangerous to nearby communities and why they would be dangerous. (3 pts)
e. In the space below, sketch a cross-section through this plate tectonic setting, from the northwest corner to the southeast corner of the map (8 pts). Be as detailed as possible, scale your sketch appropriately, and use as much space as you need. Draw your cross-section to a depth of 600 kilometers, and make sure to label and enumerate both axes of your sketch. Please scan your sketch or take a picture of it and insert it into your document before uploading to Bb.
Your sketch must also include the following :
o Label the crust, mantle, lithosphere, and asthenosphere, making sure to clearly differentiate each of these.
o Indicate the locations you would expect earthquakes to occur, using stars.
o Circle and label the location where you would expect the first partial melts in this plate tectonic setting to be generated.
o Indicate where any volcanoes would be found.
4. (15 pts)Magmatism is an important process in the formation and evolution of the Earth’s crust. Use what you’ve learned about magma generation and evolution to help you answer the following questions.
d. What is the chemical composition of the primary magma that is formed when melting first takes place? Be specific – ‘silicate’ is too vague a term here. (1 pts)
e. Explain why the chemical composition of the primary magma is the same as or different than the chemical composition of the rock that partially melted to create it. (2 pts)
f. In one sentence, explain why the resulting magma rises toward the surface. In a second sentence, explain whether or not all magma makes it to the surface to become lava. (1 pts)
Layered igneous intrusions represent the most economically valuable deposits of platinum group elements in the world. Answer the following questions about the Skaergaard Intrusion, a 2.5 km thick sill of basaltic magma that intruded into the upper crust in Greenland 55 million years ago.Sketch a schematic cross-section through this intrusion in the space below (5 pts), and then answer the following questions. Please scan your sketch or take a picture of it and insert it into your document before uploading to Bb.
g. The hot basaltic composition magma intruded into the relatively cold upper crust, causing the magma at the outer margins of the intrusion to chill quickly and solidify. Will the resulting rock be fine-grained or coarse-grained? Why? Add this to the sketch above. (1 pt).
h. What will be the first mineral to crystallize from the remaining, slowly-cooled body of magma in the center of the intrusion? What is the name of the convention or ‘series’ that categorizes the minerals by their order of crystallization? Draw the ultimate location of these crystals in your sketch above. (2 pts)
i. After the first mineral crystallizes, how has the chemical composition of the magma that is left over evolved? (1 pt)