You may also want to refer to fig 3 6 7 1 what type

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Use the figure below to answer the following questions. You may also want to refer to Fig. 3 & 6-7 . 1. What type of metamorphism occurs at low temperature and high pressure? ____________________________ What letter on the chart corresponds to these conditions? ____________________________________________ 2. Rocks near a magma chamber undergo contact metamorphism at varying temperatures and _______ pressure. What letter on the chart corresponds to contact metamorphism? _______________________________________ 3. Give the rock name that best matches the conditions for each location and the protolith. Location 1: shale protolith ____________________ Location 3: shale protolith ____________________ Location 2: basalt protolith ___________________ Location 4: limestone protolith_________________ 4. If the rock at location 1 continued to be buried to a depth of 10 km and temperatures of 325-425 o C, what rock would it become? ___________________________________________________________________________ What changes would occur in the rock as a result? _________________________________________________ 5. If the rock at location 4 were heated to temperatures of 750 o C, what rock would it become?______________ What changes would occur in the rock as a result? __________________________________________________ 6. Think back to the various metamorphic rocks you have examined in lab. Why do the rocks with a shale pro- tolith have more noticeable changes with pressure and temperature than those with a quartz sandstone protolith? __________________________________________________________________________________________ __________________________________________________________________________________________ 7. List at least two protoliths that are poor indicators of metamorphic grade?_____________________________ __________________________________________________________________________________________
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Lab #4: Metamorphic Rocks 77 Activity 2: Metamorphism and Plate Tectonics 1. Fill in the rock name that corresponds with the appropriate protolith on the diagram below. Consider the meta- morphic conditions at each location. The eclogite sample has been done for you. Hint : Keep in mind that although this diagram depicts a subduction zone, it also shows other types of metamor- phism. 2. Draw the isotherms on the diagram below (refer to the pre-lab reading). To help you, the 500 o C isotherm has been drawn as a dotted line. Note that the isotherm is not a straight line. The cooler subducting lithosphere and the hotter magma cause the isotherm to bend. Hint : All isotherms should behave similarly, so use the 500°C isotherm as a guide. Keep in mind that the coolest magma is >800 o C, and the asthenosphere is about 1,300 o C. magma Protolith: shale Protolith: peridotite Protolith: granite Protolith: sandstone Protolith: basalt Protolith: basalt Eclogite oceanic crust oceanic lithosphere 500 o C asthenosphere asthenosphere A B Oceanic Geothermal Gradient 200 o C 400 o C 800 o C 1000 o C
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Lab #4: Metamorphic Rocks 78 3. The rate at which the temperature increases with depth is called the geothermal gradient. a. When the isotherms are more closely spaced, is the temperature changing more quickly or more slowly? Circle one. b. On the diagram on the previous page there are two vertical lines marked A and B. These lines are of equal length (representing about 50 km on the diagram), but the geothermal gradient of line A is consistant, whereas the geothermal gradient of line B is inconsistant. Calculate the average geothermal gradient for each of these lines. Show your work (no calculations, no credit).
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