Magma+ActivitySp21-1

Plenge Sp21- Tectonic locations and magma formation (25 pts) Name__________________ 1. Label the boundaries/hot spots. 2. Fill in the blanks 1 Continental collision Continental divergence/hot spot Subduction zone Mid-oceanic ridge Oceanic hot spot If oceanic crust is present Options for below: Melting processes: Decompression High temperature Chemistry: Felsic/ intermediate/ mafic, water content Compositions : Mafic, Felsic, Intermediate If magma is generated by melting of oceanic crust, melting occurs due to (process + chemistry): High temperature and water content If magma is generated by melting in the mantle, melting occurs due to (process): Decompression If magma is generated by melting of the continental crust, melting occurs due to (process + chemistry): Felsic minerals together with high temperature If continental crust is present Composition is: Mafic/Intermediate/Felsic (most common is intermediate) Composition is: Felsic (though other compositions possible) If mantle upwelling occurs Composition may be: Mafic/Intermediate/Felsic Composition is: Mafic (other compositions are unlikely unless continental crust is evident)

Plenge Sp21- Tectonic locations and magma formation (25 pts) Name__________________ 3. The solid line on the graph below shows how temperature & pressure are related to phase. Use the slope of the line to help you select the true statement. a. The higher the pressure is, the easier it is to melt a rock b. It is impossible to melt a rock by changing the pressure only c. Rocks near Earth’s surface melt at lower temperatures than rocks found deep inside the Earth 4. Use the graph above to answer the following questions. Assume the solid line represents “intermediate” composition minerals. a. Line “A” represents the liquid/solid line for: (select one) i. Felsic minerals ii. Mafic minerals iii. “wet” minerals b. Line “B” represents the liquid/solid line for: (select one) i. Felsic minerals ii. Mafic minerals iii. “wet” minerals c. Line “C” represents the liquid/solid line for: (select one) i. Felsic minerals ii. Mafic minerals iii. “wet” minerals 5. On the blank graph on the right, a. Draw an arrow on the graph illustrating the movement of subducting crust from near-surface to subsurface conditions. (in word, use insert  shape  line) b. Draw the liquid-solid line (A, B, or C from the top graph) that is most relevant to melting associated with subduction. c. Explain why partial melting is observed at subduction zone boundaries using your graph. Because the subducting plate is made up of different minerals (mafic, intermediate, felsic), the melting temperatures for each is different. The added water content in the subducting plate causes the melting temperature to decrease, causing some of the minerals (usually felsic, maybe mafic) to melt. 2 Temperature Low High Pressure High Low A B C Temperature Low High Pressure High Low

Plenge Sp21- Tectonic locations and magma formation (25 pts) Name__________________ b. How does felsic magma form at these boundaries? Include both the source of the magma, the melting process, and any changes to the chemical composition of the magma in your answer. Felsic magma forms from the crust melting (making the magma more felsic in nature), due to the heat of magic magma. Partial melting/fractional crystallization changes the mafic composition to a more felsic composition. This magma then solidifies underground, and eruptions are more violent (with pyroclastic flow). 4