1. Metamorphic Petrology Review
Spring 2016

2. Important Note
Material from this review may appear on the final examination, in the same or somewhat altered form
Factors influencing the amount included on the final:
Number of students present for the review
Degree of student participation

3. What does SCMR stand for? What organization established SCMR?
The starting material from which a reaction or recrystallization begins is called what?
What does SCMR stand for?
What organization established SCMR?
Which of the following minerals might be used to characterize the onset of metamorphism?
A. Garnet
B. Zoisite
C. Omphacite
D. Prehnite
Protolith
2. Subcommission on the Systematics of Metamorphic Rocks
3. The International Union of Geological Sciences (IUGS)
4. Prehnite

4. Other minerals that characterize the onset of metamorphism are ?
Under what two conditions does intense heat promote recrystallization?
What is a mineralizer?
What is the most effective mineralizer?
Name two other common mineralizers in rocks?
Analcime, Carpholite, Glaucophane, Heulandite, Laumontite, Lawsonite, Paragonite, Pumpellyite, Stipnomelane
2. When the protolith is fine-grained
When the environment is static, since shear stresses typically reduce grain sizes
3. A substance which acts to lower a kinetic barrier - chemists would call it a catalyst
4. Fluoride ion
5. Water and carbon dioxide

5. Where might the geothermal gradient be lower than average?
Where might the geothermal gradient be higher than average?
(T-F) The Franciscan trajectory has a large increase in pressure with a relatively small increase in temperature.
What type of stress is produced by tectonic forces?
What are three sub-categories of this type of stress?
1. In a subducting plate
2. Near an igneous intrusion
Above a hot spot
In regions with unusually high radioactive element concentration
Near zones of crustal thickening or crustal extension
3. True
4. Deviatoric stress
5. Tension σ1 > σ2, both + σ3 is negative
Compression σ1 > σ2 > σ3 (Folding)
σ1 > σ2 ≈ σ3 (Flattening)
Shear Pure shear = flattening σ1 > σ2 ≈ σ3
Simple shear Movement at an angle to σ1, like pushing at the top of a deck of cards

6. (T-F) New minerals will growth during deformation, parallel to σ1.
What conditions of σ1, σ2, and σ3 are required to produce each of the following?
Foliation, no lineation
Lineation, no foliation
Both foliation and lineation
(T-F) New minerals will growth during deformation, parallel to σ1.
(T-F) The fluid phase associated with metamorphic reactions is a liquid.
1. Foliation, no lineation σ1 > σ2 ≈ σ3
Lineation, no foliation σ1 = σ2 > σ3
Both foliation and lineation σ1 > σ2 > σ3
2. False (should be perpendicular)
3. The fluid phase associated with metamorphic reactions is a liquid.
False. It may be a gas, or a combination of gas and liquid

7. A student studies the fluid inclusions in a rock
A student studies the fluid inclusions in a rock. They form a planar array. Will careful analysis of the fluid allow the student to determine the composition of the original fluid associated with metamorphism?
What formula can be used to calculate lithostatic pressure in near-surface environments?
Probably not. Planar arrays are usually formed by post-metamorphic fluids seeping into the rock along cracks
2. Lithostatic pressure = ρgh

8. Name six sources of metamorphic fluids.
Below a certain depth, around 10 km, the pressure at the point of mineral contact, Plith, will be very much greater than the pressure exerted by the intergranular fluids on the minerals. One of two things may happen to reduce this imbalance. What are they?
Name six sources of metamorphic fluids.
(T-F) The effects of contact metamorphism are most evident in shallow, low-pressure environments.
1. A. The mineral grains deform, and compress the pore space until Pfluid = Plith.
B. Pressure Solution occurs. Minerals at the stressed contacts between grains have a higher free energy than adjacent grains not in contact. They may dissolve and be reprecipitated in the pore space. This lowers the overall free energy of the system, and also allows the grains to move closer together, as well as filling the pore spaces. This continues until Pfluid = Plith.
2. a. Meteoritic water
b. Juvenile Water
c. Water associated with subducted material
d. Sedimentary brines
e. Water from metamorphic dehydration reactions
f. Degassing of the mantle
3. True

9. Are relict structures preserved in hornfels and granofels?
What is the difference between a hornfels and a granofels?
What is pyrometamorphism? How might it occur?
Where would orogenic metamorphism occur?
(T-F) Many orogenic episodes produce repeated episodes of deformation and metamorphism, leaving a polymetamorphic imprint
Yes
2. Hornfels are fine-grained, granofels are coarser
3. Pyrometamorphism is a very high temperature type of contact metamorphism. Xenoliths which fall into magma chambers may be rapidly heated, and show substantial alteration. Wall rocks in or near volcanic necks are another example. Partial melting of country rock is common.
4. Island arcs, continental arcs, or continental collision zones
5. True

10. Describe the agents at work in burial metamorphism
In sedimentary basins, sediments may accumulate to thicknesses of ten kilometers or more. The conditions near the bottom of the pile may be just enough to produce low-grade metamorphism. The Southland Syncline in New Zealand is one example. What kind the main kind of sediments present, and how does that affect the metamorphism?
What is a major difference between orogenic metamorphism and burial metamorphism?
1. Load pressure, temperature due to geothermal gradient
2. The sediments were mainly volcanoclastics, fine glassy material that is very prone to reaction.
3. The largest difference is the lack of significant structural deformation during burial metamorphism

11. What are the principal agents of metamorphism involved with ocean-floor metamorphism?
Ocean-floor metamorphism involves considerable chemical replacement. What elements are principally involved? What is the source of the new ions?
Basalt, altered by ocean-floor metamorphism, often retains the structures of basalt, including vesicles and pillow structures. The altered rock is called what?
1. Metasomatism and temperature
2. The major replacement is of Ca and Si by Mg and Na. Sodium and magnesium come from sea-water, which infiltrates rock near the magma-wall rock boundary.
3. Spilite

12. What is the agent associated with fault-zone metamorphism?
Chlorite-quartz rocks formed by ocean-floor metamorphism may be the protolith of cordierite-anthophyllite metamorphic rocks. They have a distinct chemical signature, which no igneous or sedimentary rock has. What is this signature?
What is the agent associated with fault-zone metamorphism?
They are high in Mg, low in calcium.
2. Shear stress

13. Which of the following terms is used in place of fault-zone metamorphism?
A. Dislocation metamorphism
B. Shear-zone metamorphism
C. High-stress metamorphism
D. All of the above
The terms high-stress metamorphism and dynamic metamorphism are used for two distinct types of metamorphism. What are they? D
2. Fault-zone and Impact metamorphism

14. What is the difference between fault gouge and fault breccia?
(T-F) All minerals show the transition from brittle to ductile under very similar conditions.
What two minerals are considered characteristic of impact metamorphism? What other material is often found in impact zones?
Describe two other features that are commonly associated with impacts.
Metamorphism produced by increasing temperature and pressure is called _____________________ metamorphism.
1. Fault breccia is broken, crushed rock filling in along the fault. Gouge is a clayey alteration of the breccia, produced by groundwater percolating down the fault zone.
2. False. Quartz remains brittle long after calcite is ductile.
3. Coesite and/or stishovite, high-pressure polymorphs of silica, are the characteristic minerals. Amorphous glass, produced by impact melting, is often present.
4. Shocked quartz, characterized by the presence of shocl lamallae, and shatter cones are often seen.
5. Prograde

15. (T-F) Prograde metamorphic reactions are exothermic.
Metamorphism produced by decreasing temperature and pressure is called _____________________ metamorphism.
During most types of metamorphism, equilibrium is thought to be obtained, and to prevail during on-going metamorphism. This idea is given what name?
(T-F) Prograde metamorphic reactions are exothermic.
Retrograde reaction may not be possible after prograde metamorphism has occurred. Why?
Retrograde
2. Progressive metamorphism
3. False. Many are dehydration or decarbonation reactions, both of which require energy.
4. Prograde reaction drive off water and carbon dioxide. If the volatiles are lost, the retrograde reactions will be impossible.

16. The term psammitic refers to what?
Many of the reactions used for geothermobarometry are exchange reactions. Why?
Name and briefly discuss six major categories of protolith rocks for metamorphic reactions? Indicate the places these rocks might be found, and their characteristic chemistries.
The term psammitic refers to what?
Which British petrologist made one of the first systematic studies of metamorphic rocks types, their variation, and the mineral assemblages generated in an episode of progressive metamorphism? Hint: His study area was the Scottish Highlands.
An exchange reaction, like Mg-Fe on different sites within a crystal structure, or between mineral phases, do not require a great deal of energy. They tend to stay in equilibrium with the surroundings until temperatures fall to a low level and the reactions become sluggish.
2. a. Ultramafic rocks - Mantle rocks, cumulates, and komatites. Characteristic chemistry: Very high Mg, Fe, Ni, and Cr
b. Mafic rocks - Basalts, gabbros, some graywackes. Characteristic chemistry: High Mg, Fe, Ca
c. Pelitic Rocks - Fine-grained clastic clays and silts, deposited either on stable platforms or in offshore wedges. Characteristic chemistry: High Al, K, and Si
d. Calcareous rocks: Sedimentary limestones and dolostones. Marls are impure carbonates which contain sand or shale, and thus may be richer in elements associated with pelitic rocks. Characteristic chemistry: High Ca, Mg, and CO2.
e. Quartz rocks - Oceanic cherts, composed of radiolarian skeletons, or high-energy continental sand deposits, which are nearly pure quartz. Characteristic chemistry: SiO2
f. Quartzo-feldspathic rocks - Arkosic sediments, granitoid or rhyolitic igneous rocks. Characteristic chemistry: High Si, Na, K, and Al
3. A mixture of sand and shale, which may become a protolith.
4. George Barrow

17. Did Barrow find a greater change in the sandstones or the pelitic rocks he studied?
Barrow defined a series of metamorphic zones based on the presence of index minerals for his Scottish Highlands site. Name the six zones, and describe the rocks characteristically associated with each zone. Also describe the minerals which might be associated with each zone.
Who introduced the term isograd for that boundary that separates Barrovian zones?
The pelitic rocks, whose protolith was shale, showed a much greater change. 2.
Chlorite zone - Slates or phyllites
Minerals: Chlorite, muscovite, quartz, albite
Biotite zone - Phyllites, schists
Minerals: Biotite, chlorite, muscovite, quartz, albite
Garnet zone: Garniferous schists
Minerals: Red almandine garnet, biotite, chlorite, muscovite, quartz, albite or oligoclase
Staurolite zone: Schists
Minerals: Staurolite, biotite, muscovite, quartz, garnet and plagioclase
Kyanite zone - Schists
Minerals: Kyanite, biotite, muscovite, quartz, and plagioclase, ±garnet, ±staurolite.
Sillimanite zone - Schists and gneisses
Minerals: Sillimanite, biotite, muscovite, quartz, plagioclase, and garnet, ±staurolite, ±kyanite.
3. C.E. Tilley

18. (T-F) It is possible for an index mineral to be present in a zone of higher grade than its own.
(T-F) Barrovian zones were developed in an area of rather narrow compositional range. In regions with different compositions, the use of additional or replacement index minerals may be appropriate.
(T-F) When andalusite is present, the pressure at the time of formation exceeded 0.4 GPa.
(T-F) Cordierite has a large molar volume, which indicates it is stable at low pressures.
True
3. False
4. True

19. (T-F) At very low metamorphic grade, reaction rates are slow.
(T-F) Ca-bearing minerals, like laumonite, prehnite, and pumpellyite are stable in water-rich, carbonate-free fluids.
The Sanbagawa belt lies nearer the subduction zone than the Ryoke belt. Which belt is richer in alkaline elements?
Parallel belts like the Sanbagawa and Ryoke belts, usually separated by a fault, are seen in a number of regions around the Pacific Ocean. What name did Miyashiro give to such belts?
True
2. True
3. Sanbagawa. The Sanbagawa belt is formed from the oceanward accretionary wedge, with a mixture of arc-derived sediments and volcanics mixed together with oceanic crust and marine sediments. It is the marine sediments that contribute the high sodium content necessary to form glaucophane.
4. Paired Metamorphic belts

20. Phyllonites are foliated cohesive rocks rich in what mineral?
Among petrologists, the Crestmore Quarry in California is very famous. For what is it famous? How did it form?
(T-F) Rock materials formed under high-strain conditions may be either cohesive or non-cohesive.
Non-foliated cohesive rocks include microbreccias and cataclasites. How do they differ?
Phyllonites are foliated cohesive rocks rich in what mineral?
A cohesive high-strain rock that has undergone significant recrystallization is known as what?
Under extreme conditions, frictional heating will produce partial melting, creating glass. Rocks with glassy seams are called what?
The Crestmore Quarry in Los Angeles California is a world famous location for contact pyrometamorphism involving metasomatism. A quartz monzonite porphyry was intruded into Mg-bearing carbonates. The country rock had experienced an earlier metamorphic event, and were brucite-bearing calcitic marbles. The temperatures involved at Crestmore were high enough to make this a case of pyrometamorphism. Considering the shallow depth (as evidenced by low pressure minerals) this is very unusual, seen in only a few places on earth.
2. True
3. Microbreccias have less than 70% clasts. Cataclasites have more than 70% clasts
4. Mica
5. A blastolmylonite
6. Pseodotachylyte

21. Who first formulated the idea of metamorphic facies?
(T-F) According to Bell and Etheridge, mylonization was a ductile process, with rapid recovery from strain, and recrystallization, and was not a crushing process.
Who first formulated the idea of metamorphic facies?
A. C.E. Tilley
B. Pentii Eskola
C. George Barrow
D. Alfred Harker
(T-F) The original facies classification was based primarily on metamorphosed mafic rocks.
True
2. Eskola
3. True

22. What important contribution did Viktor Goldschmidt make to the study of equilibrium mineral assemblages?
In metamorphic rocks, a is a set of repeatedly associated mineral assemblages.
Who proposed the addition of the albite-epidote and hornblende hornfels facies to Eskola’s original set of five facies?
A. Eskola
B. Coombs
C. Fyfe
D. Goldschmidt
1. Goldschmidt studied a series of contact metamorphosed hornfelses whose protoliths included pelitic, calcareous, and pssamitic rocks. This provided a considerable variation in parent rock composition, but Goldschmidt found simple mineral assemblages of six or fewer major minerals in the inner zone of aureoles around granitic intrusions around the Oslo area of Southern Norway. He noted that the equilibrium mineral assemblage was related to the bulk composition, at a particular metamorphic grade, and that that pairs of minerals were consistently seen together, such as anorthite-hypersthene or diopside-andalusite..
2. Metamorphic facies
3. Fyfe

23. Who proposed the addition of the granulite, epidote amphibolite, and glaucophane schist facies to Eskola’s original set of five facies?
A. Eskola
B. Coombs
C. Fyfe
D. Goldschmidt
Who proposed the addition the zeolite and prehnite-pumpellyite facies to Eskola’s original set of five facies?
D. All of the above
Eskola
2. Coombs

24. In metamorphic assemblages, the symbol ± is short for what phrase?
(T-F) There is little difference in mafic rock facies that develop at low, medium, or even high pressure.
Using Yardley’s classification, identify the facies associated with each group:
A. High-pressure
B. Medium-pressure
C. Low-pressure
D. Low-grade
In metamorphic assemblages, the symbol ± is short for what phrase?
What names did Miyashiro give to his final compilation of three baric series?
True
2. High-pressure (blueschist, eclogite)
Medium-pressure (greenschist, amphibolite, granualite)
Low-pressure (albite-epidote, hornblende, and pyroxene hornfels, and the sanidinite facies)
Low-grade - (zeolite, prehnite-pumpellyite)
3. With or without
4. Low, medium, and high P/T

25. Where might a low P/T baric series be found?
A. Rift zone
B. High heat flow orogenic zone
C. Contact metamorphic zone
D. All of the above
The Barrovian type of metamorphic trajectory is characteristic of which baric series?
A. High P/T
B. Medium P/T
C. Low P/T
D. May be any of the above
All of the above
2. Medium P/T

26. What is an immature graywacke?
The Buchan type of metamorphic trajectory is characteristic of which baric series?
A. High P/T
B. Medium P/T
C. Low P/T
D. May be any of the above
(T-F) The high P/T baric series is characteristic of below normal geothermal gradients, such as in subduction zones.
What is an immature graywacke?
(T-F) Ordinary prograde metamorphic reactions are common in high-temperature mafic igneous rocks.
Low P/T
2. True
3. An immature graywacke is one that has undergone at most limited weathering. The mafic minerals have not been completely weathered out.
4. False. Ordinary prograde metamorphic reactions are not possible in these rocks, since they cannot be dehydrated.

27. If water for hydration reactions were available in high-temperature mafic igneous rocks, would coarse-grained or fine-grained rocks react faster? Why?
(T-F) Hydration reactions may release large quantities of energy, significantly heating the rocks.
(T-F) If equilibrium is maintained, there is a correlation between the An content of plagioclase and the temperature.
(T-F) In the low-grade mafic assemblages, complete alteration of the protolith minerals occurs, and it is easy to define new characteristic mineral assemblages.
1. Coarse grained rocks are usually the least permeable, and therefore the slowest to react. Tuffs and graywackes, which are permeable, will react faster. Of course, the latter rocks also have very small grain size, which facilitates reactions (higher surface area/volume ratio).
2. True. In a paper by Bucher and Frey, they estimated that the following reaction:
Clinopyroxene + Plagioclase = Prehnite + Chlorite + Zeolite
would release enough energy to elevate the temperature of well-insulated rocks by 100̊C.
3. True
4. False. Rocks in this category are usually only partly altered, and the products are extremely fine-grained, messy-looking minerals. Most workers chose to ignore them, simply calling them altered. Eskola simply wrote “formation of zeolites” in his chart. This indicated he did not believe the zeolites represented an equilibrium assemblages

28. At the high temperature end of the prehnite-pumpellyite facies, prehnite may break down to yield what mineral?
A. Actinolite
B. Hornblende
C. Enstatite
D. Forsterite
The most common regional metamorphic rocks are characteristic of what baric series?
A. High P/T
B. Medium P/T
C. Low P/T
D. May be any of the above
Actinolite
2. Medium P/T - Greenshcist, amphibolite, and granulite facies rocks are medium P/T series.

29. (T-F) In a Barrovian sequence, oligoclase appears before hornblende.
The transition from the greenschist to the amphibolite facies involves two major mineralogical changes. What are they?
(T-F) In a Barrovian sequence, oligoclase appears before hornblende.
As grade increases, the color of hornblende changes from green to brown. Why?
Hydrous pelitic and quartzo-feldspathic rocks do not reach granulite grade. Why? 1.
a. Increased Ca content of plagioclase, from albite to oligoclase, across the peristerite gap
b. Transition form actinolite to hornblende. At higher temperatures, the amphibole structure is able to accommodate more aluminum and alkali ions.
2. False. In higher pressure sequences (Barrovian) hornblende appears before oligoclase. In lower P/T terranes (Buchan), and in contact aureoles, the plagioclase appears first.
3. Due to increasing Ti content in the hornblende
4. When aqueous fluids are present, pelitic and quartzo-feldspathic rocks will be above the solidus at low to medium pressure. Melting will begin. Migmatites may form.

30. Granulites are thought to form in regions of crustal thickening. Why?
A basalt that has been hydrated to form greenstone, and then progressively metamorphosed to higher temperatures, may reach the granulite facies with a chemistry dominated by plagioclase and pyroxene, like the protolith. However, it will differ from the protolith in one important respect, which is:
Granulites are thought to form in regions of crustal thickening. Why?
1. The texture of such metabasalts is gneissic, completely unlike the parent rock.
2. Areas of crustal thickening have very high geotherms, which allows granulties to reach the ̊C range they require to form.

31. As pressure increases, amphibolite or granulite facies rocks transform to eclogites. It is the initial breakdown of which mineral that marks this transition?
A. Enstatite
B. Hornblende
C. Plagioclase
D. Garnet
Coleman first described three distinct petrologic settings eclogites are associated with in What were his three settings?
Plagioclase 2.
A. Xenoliths in kimberlites or basalts
B. Bands to lens-shaped deposits in migmatitic gneisses
C. Bands or lens-shaped deposits in blueshist

32. What temperature range is a medium temperature eclogite associated with?
A °C
B °C
C °C
D °C
(T-F) Eclogites span a greater temperature range than any other facies.
(T-F) Ecolgites associated with xenoliths in kimberlites or basalts belong to the low-temperature group.
C ̊C
2. True
3. False. They belong to the high-temperature group.

33. Eclogites associated with migmatitic gneisses are usually associated with which temperature group?
A. Low
B. Medium
C. High
D. Any of the above
A metamorphic rock will typically be buried, metamorphosed, possibly with orogenic forces acting on it, then brought to the surface through uplift and erosion. The path that it follows is called a __________________ path.
B Medium
2. P-T-t

34. Describe three ways we can gain information about P-T-t paths.
(T-F) Greenschist-amphibolite facies, such as those of Western North Carolina, require an average continental crustal geotherm to form.
Where does the extra heat come from?
Which path is associated with orogenic belt crustal thickening?
A. a
B. b
C. c
D. All of the above 1.
A. We can look for partial overprints of one mineral assemblage on another. Relict minerals may include part of the path, either prograde or retrograde. We have previously seen that equilibrium is apt to be maintained during prograde metamorphism. Relict minerals reflecting prograde metamorphism are therefore relatively common. The necessity for hydration reactions to occur during retrograde metamorphism makes the maintenance of equilibrium more difficult. Nevertheless, relict minerals reflecting retrograde paths have been observed.
B. We can apply the techniques of geothermometry and geobarometry to studies of core to rim changes in the geochemistries of individual, chemically zoned, mineral grains. Electron microprobes have greatly enhanced our ability to do this. Other techniques can be used as well. These include oxygen isotope geothermometry, data from fluid inclusions, and isotopic cooling ages, such as the 40Ar/39Ar method. All of these methods are examples of "reverse" methods. They begin with studies of the product, and attempt to determine the process that created the product. At best, they give us clues to part of the P-T-t path.
C. We can use heat-flow models to theoretically recreate complete P-T-t paths. These models are evaluated by comparison with the partial data obtained from the reverse methods.
2. False
3. Crustal thickening, associated with the plate collisions that produced the orogenic episodes.
4. A. a

35. Used on the following two slides

36. What does path “b” represent?
(T-F) Path “c” is common in high-grade gneiss, and granulite facies terraines.
What produces path “c”?
Retrograde reactions, where water is lacking, are slow. Granulite facies rocks may show retrograde metamorphism. Why, since these rocks are usually anhydrous?
(T-F) Counterclockwise P-T-t paths are found only in granulite facies rocks.
Path "b" represents a situation in which at rock is heated and cooled under nearly isobaric conditions.
2. True
3. It is believed to result from the intrusion of large quantities of mafic magma into the lower to middle crust. The intrusion causes a rapid rise of both temperature and pressure below the intrusions. The high density of the mafic rock does not allow uplift. Thus rock below the intrusion cools isobarically without uplift and erosion.
4. The rocks are held at high temperatures for long periods, and may re-equilibrate during cooling. When rocks are held at high temperatures for long periods retrograde reactions may be more important.
5. False. A study by Spear of Acadian orogeny rocks in the northeastern part of the U.S. found two different regimes. In the western part, a high-pressure (≼ 1 GPa) Barrovian trajectory shows a clockwise P-T-t path. In the eastern region, a lower-pressure (< 0.5 GPa) zone shows a Buchan trajectory, with a counterclockwise P-T-t path. The clockwise path is thought to result from crustal thickening followed by erosion and resultant cooling. The counterclockwise path is thought to result from crustal extension, which allowed many syntectonic plutons to intrude, possibly supplying enough heat to partially melt the lower crust.

37. (T-F) For most paths, Pmax and Tmax occur at the same time.
P-T-t diagrams are deceptive in one very important respect. What is it?
(T-F) For most paths, Pmax and Tmax occur at the same time.
For path “a”, do pressure and temperature increase together?
(T-F) Metamorphic grade is most closely related to Pmax.
(T-F) Blueschist preservation, rather than blueschist generation, may be more important in determining whether blueschist rocks are seen in a region.
Time is not shown explicitly. The direction of movement is indicated, but the rate of progress can be quite different in different parts of the curve.
2. False. They often differ considerably. Pressure and temperature do not increase together. The relative changes in both quantities with time vary considerably along the path. This is an important difference with the traditional view of regional metamorphism.
3. Pressure and temperature do not increase together. The relative changes in both quantities with time vary considerably along the path. This is an important difference with the traditional view of regional metamorphism.
4. False. It is much more closely related to conditions around Tmax.
5. True

38. What are you seeing?
SPOTS!
Please do them TODAY!