Name: Daniel Gaughan
Melting Rocks:
Using Graphs to Determine When A Rock Becomes Molten
Use the graph below (Figure 4.19 out of T&L 8
th
Ed.) to answer the following questions.
1. At what approximate temperature does “dry basalt” melt when it exists at a depth of 20 km?
1200
2. At what approximate temperature does “dry basalt” melt when it exists at a depth of 30 km?
1250
3. Pressure increases with depth. Thus, the pressure at 30km beneath the surface is higher than at 20km beneath the surface. Using this information and your answers to #1 & #2: Is it easier or more difficult to melt the same rock but at a higher pressure? How do you know?
Its harder because you have to use higher temperatures the deeper you go
4. At what approximate temperature does “dry granite” melt when it exists at a depth of 20 km?
950
5. Using your answers to #1 & #4, which composition melts at a lower temperature (at the same depth/pressure) -- Granite or Basalt?
Granite
6. At what approximate temperature does “wet granite” melt when it exists at a depth of 20 km?
650
7. Using your answers to #4 & #6, Is it easier or more difficult to melt the same rock but with a higher amount of water/steam/vapors (i.e., a
“wet” rock)? How do you know?
Its easier because at the same depth you need significantly less heat to melt the rock when its wet
