1. What are the two main agents of metamorphism, and what are their respective roles in producing metamorphic rocks?
Answer: Heat and pressure are the main agents of metamorphism. Heat leads to mineralogical changes in
the rock. Pressure also influences those mineralogical changes, while directed pressure (greater
pressure in one direction) leads to foliation.
2. What types of metamorphic rocks will form if a mudrock experiences very low, low, medium, and high-grade metamorphism?
Answer: Very low grade: slate; low grade: phyllite; medium grade: schist; high grade: gneiss.
3. Why doesn’t granite change very much at lower metamorphic grades?
Answer: Granite remains largely unchanged at lower metamorphic grades because its minerals are still
stable at those lower temperatures.
4. Describe the main process of foliation development in a metamorphic rock such as schist.
Answer: Foliation develops in schist when new platy minerals grow with their longest dimension at a right
angle to the direction of greatest pressure.
5. What process contributes to metamorphism of oceanic crust at a spreading ridge?
Answer: At a spreading ridge the heat from volcanism leads to the development of a groundwater
convection system in the rock of the oceanic crust. Heated water rises in the hot regions and is
expelled into the ocean, while cold ocean water is drawn into the crust to replace it. The heated
water leads to the conversion of olivine and pyroxene into chlorite and serpentine.
6. How do variations in the geothermal gradient affect the depth at which different metamorphic rocks form?
Answer: The geothermal gradient varies as a function of tectonic setting, being greatest in volcanic regions
and lowest along subduction zones. As a result the depth at which specific metamorphic grades is
achieved will vary: the depth will be greater when the gradient is lower.
7. Blueschist metamorphism takes place within subduction zones. What are the particular temperature and pressure characteristics of this geological setting?
Answer: The geothermal gradient is low within subduction zones because the cold subducting oceanic crust
takes a long time to heat up. Pressure increases with depth at the normal rate, but temperature does
not.
8. Rearrange the following minerals in order of increasing metamorphic grade: biotite, garnet, sillimanite, chlorite.
Answer: Order of increasing metamorphic grade: chlorite, biotite, garnet, sillimanite.
9. What is the role of magmatic fluids in the metamorphism that takes place adjacent to a pluton?
Answer: Water from any source facilitates metamorphism. Magmatic fluids typically contain dissolved ions
at higher concentrations than in regular groundwater (especially copper, zinc, silver, gold, lithium,
beryllium, boron and fluorine), leading to the formation of a unique set of minerals.
10. How does metasomatism differ from regional metamorphism?
Answer: Metasomatism involves fluids from magmatic or groundwater sources that play an important role
in transporting ions into the system, and leading to the formation of new minerals. Regional
metamorphism takes place over a larger area, depends more on plate tectonic conditions, and does
not involve flushing the system with large amounts of fluid.
11. How does the presence of a hot pluton contribute to metasomatism?
Answer: A hot pluton heats the surrounding water, causing groundwater to convect. This can result a great
deal of water, in some cases with elevated levels of specific ions, passing through the rock. Water
from magma within the pluton also contributes to metasomatism.
12. What determines whether metasomatism will produce skarn?
Answer: Limestone must be present to produce skarn.
13. For each of the following metamorphic rocks, indicate the likely parent rock and the grade and/or type of metamorphism: chlorite schist, slate, mica-garnet schist, amphibolite, marble.
Answer: Parent rocks and metamorphic grades and types:
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