Page 86 - Laboratory Manual in Physical Geology

C. REFLECT & DISCUSS Based on your answers above, what are two environmental changes that can cause the peridotite at
point X (see FIGURE 2.8 ) to begin partial melting?

D. Obtain the materials shown in FIGURE 2.9 . Turn the hot plate on a low setting (about 3 on most commercial hot plates)

and allow it to heat up in a safe location. Next place two sugar cubes on a flat piece of aluminum foil. Label (on the foil)
one sugar cube “dry.” Moisten the second sugar cube with a few drops of water, and label it “wet.” Carefully place the
aluminum foil (with the sugar cubes) onto the hot plate and observe what happens. ( Note: Turn off the hot plate when

one cube begins to melt.)

1. Which sugar cube melted first?

2. The rapid melting that you observed in the moistened sugar cube is called “ flux melting,” because flux is a material that
promotes (speeds up) melting. What was the flux?

3. How would the P-T diagram in FIGURE 2.9 change if all of the peridotite in the diagram was “wet” peridotite?

4. In what specific kind of plate tectonic setting could water enter Earth’s mantle and cause flux melting of mantle peridotite?
( Hint: FIGURE 2.3 )

E. REFLECT & DISCUSS Examine this cross section of a plate boundary.

1. What kind of plate boundary is this?

2. Name the specific process that led to the formation of magma in this cross section.

3. Describe the sequence of plate tectonic and magma generating processes that led to formation of the volcanoes (oceanic

ridge) in this cross section.

Continental Oceanic Continental
crust ridge crust

Oceanic crust

Lithosphere Lithosphere

Magma
Asthenosphere

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