Geology 407a Petrology

Exam 2 Study Guide

Intermediate rocks (plutonic and volcanic)

Felsic plutonic rocks: Granitoids (diorite, quartz diorite, tonalite, granodiorite, granite, etc.)


Introduction to Metamorphism

Metamorphic protoliths

Metamorphic facies

Equilibrium and the phase rule.

Graphical representation - composition diagrams

Metamorphic Reactions

Reading metamorphic reactions off composition diagrams


Calcareous rocks

Metamorphism and tectonics


Some review questions:

1) How is magma differentiation thought to occur in plutons?

2) Fill in the names of metamorphic facies in the appropriate places on the P-T diagram.

3) Describe the metamorphism that occurs at mid ocean ridges. Include process, resulting mineralogy, and potential ore deposits in your discussion.

4) Using your ideas from question 3, explain why blueschists that we see today have amphiboles with cores of actinolite and rims of glaucophane. In line with this, why do subducting slabs dehydrate at depth to produce the fluids so vital to production of arc magmas in the overlying mantle wedge?

5) Describe what is meant by a Barrovian metamorphic sequence and include the characteristic index minerals. What facies do these index minerals represent? How does this differ from Buchan metamorphism?

6) What is the mineral diagnostic of a metabasic protolith that exists throughout the entire P-T region of metamorphic facies?

7) Why are hornfelsic rocks fine grained and granoblastic? What would favor the growth of a porphyroblast?

8) Why doesn't zeolite facies metamorphism show up in all protolith types?

9) What is the difference between thermal and dynamic metamorphism?

10) What is an isograd?

11) What is the concept of facies series?

12) Discuss the difference between the first and second sillimanite isograd.

13) ***Be able to discuss the chemical characteristics of various metamorphic protoliths and the types of minerals they develop during progressive metamorphism.***

14) Why is the phase rule useful?

15) Understand the concept of composition diagrams and how they can help you deduce a reaction. Also understand how they can be used to graphically illustrate a change in facies.

16) What differences in mineralogy would you expect during progressive metamorphism in pure carbonates versus impure carbonates, versus marls.

17) Understand the difference between a discontinuous versus a continuous reaction.

18) Understand the difference between solid-solid and solid-fluid reactions.

19) Why are amphiboles stabilized in metabasic rocks and micas stabilized in metapelites?

20) What are the important mineralogical changes that occur in metabasic rocks as they go from zeolite to greenschist to albite-epidote amphibolite to amphibolite to granulite facies? (i.e. how do you recognize what facies a metabasic rock is in?). How do these relate to the mineralogical changes in pelites during the same facies changes?