Review Questions for Chapter 21: An Introduction to Metamorphism
1. What defining processes may occur during metamorphism? Briefly describe each.
2. Into what does metamorphism grade at the low-grade end?
How do we define the low-grade boundary of metamorphism?
Why is this a rather difficult distinction to make?
3. Metamorphism grades into what at the high-grade end?
How do we define the high-grade boundary of metamorphism?
Why is this a rather difficult distinction to make?
4. In what ways may changing temperature affect metamorphic mineral assemblages and textures?
5. What is a metamorphic field gradient, and how do they differ from a geothermal gradient (at the
time of metamorphism)?
Describe a situation in which a metamorphic field gradient and a geothermal gradient would be the
same.
6. What is lithostatic pressure?
What would be the shape of a strain ellipsoid for rocks experiencing lithostatic pressure?
7. How does flattening differ from shear?
8. Suppose you had a deformed rock with cleavage and markers (such as fossils, oolites, etc.) that
permitted you to determine a strain ellipsoid, as in the figure below. Can you distinguish whether
either rock has been deformed by flattening or shear? Explain.
9. Think of a common object with a shape corresponding to the strain ellipsoid for each of the
following stress situations. Also state for each whether particles contained within your object
should conform to a foliation or lineation.
a. 1 > 2 = 3
b. 1 = 2 > 3
c. 1 > 2 > 3
10. Describe two plausible ways that pH2O could be less than Ptotal.
11. Cite one major reason why Pfluid is probably equal to Plith during prograde metamorphism.
12. Why might Pfluid be much less than Plith after metamorphism has passed its peak?
13. What is metasomatism?
14. Describe a typical field occurrence of contact metamorphism.
What typically causes it?
How might the contact metamorphic rocks vary spatially, and over what scales?
What kinds of textures are typical of contact metamorphism?
15. Describe a typical field association of regional metamorphism.
What typically causes it?
How might regional metamorphic rocks vary spatially, and over what scales?
What kinds of textures are typical of regional metamorphism?
16. Why might relict textures be more common in contact metamorphism than in regional?
In what part of a contact aureole are relict textures most likely to occur? Why?
17. Describe a typical field association of fault-zone metamorphism. What kinds of textures are typical
of fault-zone metamorphism?
18. What is prograde metamorphism?
What is retrograde metamorphism?
Which is more likely to be maintained? Why?
19. What is meant by the term progressive metamorphism?
At what metamorphic grades is it less likely to occur? Why?
20. What are the six most common types of metamorphic protolith? What chemically characterizes
each?
21. What are metamorphic zones?
What is an isograd?
What is an index mineral?
How are zones conventionally named? Be specific and give an example, specifying the lower and
upper boundaries.
How does the stability range of an index mineral compare to the limits of the zone named for it?
22. What does the notion of progressive metamorphism imply for the geometry and location of
isograds over time during a metamorphic event? In what way would you expect them to change?
Why?
23. How did the conditions and metamorphic field gradient of metamorphism along the Buchan coast
of Scotland differ from that in the classical Barrovian area?
24. What are paired metamorphic belts?
How does the outer belt differ from the inner belt in terms of P/T gradient and setting? Explain
why.