GLY4310
88 points
16 took exam
Name
April 24, 2015
Florida Atlantic University
PETROLOGY -- FINAL EXAMINATION KEY
Scores to the left of the answer in red are the number of incorrect responses. Instructor comments and
answers are in blue.
True-False - Print the letter T or F in the blank to indicate if each of the following statements is
true or false. Illegible answers are wrong. (1 point each)
0
T
1. Barrow found a much greater change in the pelitic rocks he studied, compared to the
sandstones.
0
T
2. Ca-bearing minerals, like laumonite, prehnite, and pumpellyite are stable in waterrich, carbonate-free fluids.
1
F
3. Ordinary prograde metamorphic reactions are common in high-temperature mafic
igneous rocks.
0
F
0
F
1
T
6. Hydrous pelitic and quartzo-feldspathic rocks do not reach granulite grade.
0
T
7. Cordierite has a large molar volume, which indicates it is stable at low pressures.
0
T
8. The presence of garnet in a facies indicates it formed at medium to high pressures.
1
F
9. When andalusite is present, the pressure at the time of formation exceeded 0.4 GPa.
2
F
10. Counterclockwise P-T-t paths are found only in granulite facies rocks.
6
F
11. Around catazonic plutons, contact metamorphic aureoles arm narrow and easily
distinguished from country rock.
3
T
12. At very low metamorphic grade, the preservation of original igneous textures and
minerals is common.
4. For most P-T-t paths, Pmax and Tmax occur at the same time.
5. In the low-grade mafic assemblages, complete alteration of the protolith minerals
occurs, and it is easy to define new characteristic mineral assemblages
1
2
T
13. A metamorphic facies may be defined as a set of repeatedly associated mineral
assemblages.
1
F
14. All minerals show the transition from brittle to ductile under very similar conditions.
1
T
15. Blueschist preservation, rather than blueschist generation, may be more important in
determining whether blueschist rocks are seen in a region.
7
F
16. Cataclasis refers to mechanical crushing and grinding, with no recrystallization.
Rocks exhibiting this behavior have undergone ductile flow.
4
T
17. Because there is little difference in mafic rock facies that develop at low, medium, or
even high pressure, the biggest argument for the inclusion of the low pressure facies
comes from the pelitic rocks.
5
F
18. High pressure favors the formation of low density phases.
2
T
19. The continental geotherm is considerably higher than the oceanic geotherm, due to LIL
elements, which concentrate in continental crust and generate significant heat.
8
F
20. Both lithospheric and deviatoric stress can produce deformation in rocks.
1
T
21. Eclogites span a greater temperature range than any other facies.
0
F
22. New minerals will growth during deformation, parallel to σ1.
1
T
23. The effects of contact metamorphism are most evident in shallow, low-pressure
environments.
0
T
24. Many orogenic episodes produce repeated episodes of deformation and
metamorphism, leaving a polymetamorphic imprint.
1
F
25. Prograde metamorphic reactions are exothermic.
1
T
26. Rock materials formed under high-strain conditions may be either cohesive or
non-cohesive.
2
F
27. Ordinary prograde metamorphic reactions are common in high-temperature mafic
igneous rocks.
3
T
28. Although garnets exhibit hexoctahedral isometric structures, they rarely appear are
cubes or octahedrons. The atomic population of the {100} and {111} family of planes is
depleted, resulting in this seemingly strange behavior.
2
7
F
29. Hemimorphite and often amorphous chrysocolla are primary minerals formed in the
oxidized portions of zinc and copper deposits, respectively. They are good indicator
minerals for potential ores beneath them. As the description indicates, they are
secondary, not primary.
10
T
30. In the system Forsterite-Nepheline-Silica as pressure increases the eutectic shifts
away from silica apex.
Multiple-Choice - Choose the best response to each statement or question. Print the letter
corresponding to your choice in the blank. (1 point each)
0
D
1. Fluid may refer to:
A. Liquid
B. Gas
C. A single phase above the critical point
D. All of the above
1
C
2. Xenoliths which fall into magma chambers may be rapidly heated, and show
substantial alteration, or wall rocks in or near volcanic necks may show a type of contact
metamorphism known as:
A. Burial metamorphism
B. Hydrothermal metamorphism
C. Pyrometamorphism
D. None of the above
13
B
3. In the English Lake District, Ordovician Skiddaw Slates are intruded by granite and
granodiorite bodies. The metamorphic aureole is divided into the inner, middle, and outer
zones. The basis for this classification within the zones is:
A. Mineralogy
B. Structure
C. Temperature
D. All of the above
10
A
4. Rocks that contain cordierite and andalusite are likely to have protoliths rich in which
element?
A. Al
B. Ca
C. Fe
D. Mg
3
2
C
5. Who proposed the addition of the albite-epidote and hornblende hornfels facies to
Eskola's original set of five facies?
A. P. Eskola
B. D. Coombs
C. W. Fyfe
D. V. Goldschmidt
1
C
6. 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
7
C
7. Which of the following sets of metamorphic facies is typical of rocks seen in areas
where the protolith reacts quickly, there is a high geothermal gradient, and fluids are
abundant?
A. Albite-epidote hornfels, hornblende hornfels, pyroxene hornfels, and sanidinite
B. Blueschist and eclogite
C. Zeolite and prehnite-pumpellyite
D. None of the above
2
D
8. 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
6
B
9. Who first formulated the idea of metamorphic facies?
A. C.E. Tilley
B. Pentii Eskola
C. George Barrow
D. Alfred Harker
1
B
10. Who proposed the addition the zeolite and prehnite-pumpellyite facies to Eskola’s
original set of five facies?
A. Eskola
B. Coombs
C. Fyfe
D. All of the above
4
1
B
11. 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
2
A
12. 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
11
B
13. Eclogites associated with migmatic gneisses are usually associated with which
temperature group?
A. Low
B. Medium
C. High
D. Any of the above
3
D
14. 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
3
A
15. 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
1
C
16. During ocean floor metamorphism, which pair of elements is removed from the
protolith?
A. Fe, Mg
B. Na, Mg
C. Ca, Si
D. K, Ti
5
1
C
17. A cohesive high-strain rock that has undergone significant recrystallization is known
as what?
A. Phyllonite
B. Microbreccia
C. Blastomylonite
D. Cataclasite
1
C
18. The starting material from which a reaction or recrystallization begins is called what?
A. Granofels
B. Isograd
C. Protolith
D. Spillite
1
C
19. Which of the following describes tension?
A. σ1 > σ2 > σ3
B. σ1 > σ2 . σ3
C. σ1 > σ2, both + ; σ3 is negative
D. Either A or B
0
B
20. Which of the following is the most effective mineralizer?
A, Water
B. Fluoride ion
C. Carbon dioxide
D. Sulfur dioxide
0
B
21. Where might the geothermal gradient be lower than average?
A. Near zones of crustal thickening or crustal extension
B. In a subducting plate
C. Near an igneous intrusion
D. Above a hot spot
2
A
22. Albite-epidote hornfels, hornblende hornfels, pyroxene hornfels, and sanidinite all
belong to which group of metamorphic facies, as classified by Yardley?
A. Low pressure facies
B. Medium pressure facies
C. High pressure facies
D. Low grade facies
3
A
23. The perisiterite "solvus" occurs in which plagioclase composition range?
A. An7-17
B. An27-37
C. An47-57
D. An77-87
6
4
C
24. Most exposed granulite facies rocks are found:
A. Associated with basalts and gabbros near a former ocean ridge, where the heat flow
was very high
B. Associated with shield volcanism, in areas of greatly elevated geothermal gradient
C. In deeply eroded, Precambrian rocks associated with continental shields
D. All of the above
4
D
25. Elements described as "Iron-loving" and composed of elements, typically iron and
alloying elements, which form dense phases, which are often metallic, although bonding
to sulfur or carbon is possible, belong to which Goldschmidt classification.
A. Atomphile
B. Chalcophile
C. Lithophile
D. Siderophile
4
D
26. If the weight percent alumina concentration approximately equals the weight percent
(Na2O) + (K20) concentrations, the rocks are classified as?
A. Metaluminous
B. Peralkaline
C. Peraluminous
D. Subaluminous
4
B
27. On the continuous side of Bowen’s Reaction Series, what solid solution series is
crystallizing?
A. Olivine
B. Plagioclase feldspar
C. Potassium feldspar
D. Amphiboles
Fill-Ins - Write in the word or words which best completes each statement or answers each
question. (1 point per blank)
0
1. In metamorphic assemblages, the symbol ± is short for what phrase?
WITH OR WITHOUT
3
2. Granulites are thought to form in regions of crustal thickening. Why?
AREAS OF CRUSTAL THICKENING HAVE VERY HIGH GEOTHERMS, WHICH
ALLOWS GRANULITES TO REACH THE 700-1000EC RANGE THEY REQUIRE TO
FORM.
0
3. As grade increases, the color of hornblende changes from green to brown. Why?
DUE TO INCREASING TI CONTENT IN THE HORNBLENDE
7
8
4. Non-foliated cohesive rocks include microbreccias and cataclasites. How do they differ?
MICROBRECCIAS HAVE LESS THAN 70% CLASTS. CATACLASITES HAVE MORE
THAN 70% CLASTS
5.5
5. The term psammitic refers to what?
A MIXTURE OF SAND AND SHALE, WHICH MAY BECOME A PROTOLITH.
7
6. 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?
THEY ARE HIGH IN MG, LOW IN CALCIUM.
2
7. 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?
PAIRED METAMORPHIC BELTS
2
8. Most museum meteorite collections are dominated by irons. When meteorites are collected at
fall sites, stones comprise about 94% of collected samples. Explain what causes this discrepancy.
IRONS ARE MUCH EASIER TO IDENTIFY, BECAUSE THEY ARE USUALLY
MAGNETIC, VERY DENSE, AND DON’T RESEMBLE MOST TERRESTRIAL SAMPLES.
STONES OFTEN LOOK LIKE TERRESTRIAL ROCKS, ESPECIALLY WHEN THEY
WEATHER.
9-10. The geothermal gradient varies from place to place on the earth. What are the sources of
heat, and why does it vary?
4.5
9. THE SOURCES ARE HEAT FROM THE ORIGINAL ACCRETION AND
GRAVITATIONAL DIFFERENTIATION OF THE EARTH, AS WELL AS ONGOING
CRYSTALLIZATION OF Fe-Ni ALLOY IN THE CRUST, AND DECAY OF LONG-LIVED
RADIOACTIVE ISOTOPES, WITH HALF-LIVES ON THE ORDER OF A BILLION YEARS
OR MORE, SUCH AS U, Th, AND K.
8
9
10. RADIOACTIVE ISOTOPES CONCENTRATE IN FELSIC ROCKS, SO HEAT ESCAPE
WILL BE MUCH HIGHER ABOVE FELSIC ROCKS THAN MAFIC ROCKS.
9
11. In order to justify using the IUGS gabbroic chart, what criteria must be met? P + M > 90%
7
12-13. In an ophitic texture, 12) PLAGIOCLASE LATHS are completed surrounded by
8
13)
7
14. The type of rock associated with the magma series OIA is ALKALINE BASALT
4
15. MAARS
CLINOPYROXENE crystals
are negative topographic features, with craters excavated by
hydromagmatic (phreatic) explosions. Such explosions occur when magma interacts with
meteoritic water (either surface or groundwater). The water flashes into steam, with a huge increase
in volume.
5.5
16. What is the primary reason some gabbros may melt at considerably lower temperatures than
basalt, despite similar magmatic chemistries?
BASALT MAGMAS ARE USUALLY ANHYDROUS, WHEREAS SOME GABBROIC
MAGMAS HAVE A HYDROUS COMPONENT. WATER DEPRESSES THE MELTING
POINT.
9
Diagram - Each of the following questions refers to Figure 1(1 point each)
Figure 1
2
1
A
1. Which path is associated with orogenic belt crustal thickening?
A. a
B. b
C. c
D. All of the above
2. What does path “b” represent?
PATH "B" REPRESENTS A SITUATION IN WHICH AT ROCK IS HEATED AND COOLED
UNDER NEARLY ISOBARIC CONDITIONS.
3
3. For path “a”, do pressure and temperature increase together?
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.
10
2
D
4. Which path is common in high-grade gneisses and granulite facies terranes. It is
believed to result from the intrusion of large quantities of mafic magma into the lower to
middle crust.
A. a1
B. a2
C. b
D. c
Problem - SHOW ALL WORK - there will be no credit for answers not supported by sufficient
work to justify your answer. Show the formula used in your calculation, and identify all
parameters, including units, used in the formula. Clearly label your answer, including units if
any. Be sure to express your answer to the correct number of significant figures.
22.5
Suppose a reaction takes place with a constant energy barrier of 3850 cal/mol. Calculate K at
645 C. (4 points) The energy barrier figure is good to four significant figures.
where K = equilibrium constant (dimensionless)
E = energy barrier (calories/mole)
R = gas constant = 1.987 cal/E mole
T = temperature (Kelvin) - EC + 273.15 = Kelvin
e = natural logarithm base
Once again, for a class that did very well on the homework, the results here were terrible.
11
Discussion Questions - Answer all of the following questions completely but concisely. Points
as indicated. Diagrams (labeled) may be used to supplement your written answers, where
appropriate.
14
1. In Scotland, Comrie schists were intruded by diorite. The inner aureole is granofels,
containing a mineral associations of orthopyroxene + potassium feldspar. In the English Lake
District, Ordovician Skiddaw Slates are intruded by granite and granodiorite bodies. In the
innermost zone, the rocks are hornfelsic. What is the difference between hornfels and granfels?
What is responsible for the formation of granofels rather than hornfels? (2 points)
BOTH GRANOFELS AND HORNFELS ARE NON-FOLIATED ROCKS TYPICALLY
PRODUCED BY CONTACT METAMORPHISM. THE TEXTURE OF GRANOFELS
IS CONSIDERABLY LARGER THAN HORNFELS. THE CAUSE OF THE
INCREASED GRAIN SIZE WAS HEAT, SINCE A DIORITIC MAGMA IS MUCH
HOTTER THAN FELSIC MAGMAS LIKE GRANITE OR GRANODIORITE. IN
ADDITION, SLATE IS A MUCH FINER GRAINED PROTOLITH, SO IT REACTS
FASTER, BUT IT PRODUCES SMALL GRAINS AS A PRODUCT
13
2. Mafic rocks may remain unaltered while nearby sedimentary rocks are completely changed by
metamorphism. Why? (2 points)
HIGH-TEMPERATURE MAFIC IGNEOUS ROCKS CONTAIN VERY LITTLE
WATER. ORDINARY PROGRADE METAMORPHIC REACTIONS ARE NOT
POSSIBLE IN THESE ROCKS, SINCE THEY CANNOT BE DEHYDRATED.
SEDIMENTARY ROCKS ARE QUITE WET, AND PROGRADE REACTIONS
OCCUR READILY.
9
3. The Sanbagawa belt lies nearer the subduction zone than the Ryoke belt. Which belt is richer
in alkaline elements? Why? (2 points)
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.
12
8
4. Did Barrow find a greater change in the sandstones or the pelitic rocks he studied? Why? (2
points)
THE PELITIC ROCKS, WHOSE PROTOLITH WAS SHALE, SHOWED A MUCH
GREATER CHANGE. FINE-GRAINED ROCKS, WHICH HAVE A MUCH HIGHER
SURFACE AREA TO VOLUME RATIO, USUALLY REACT MUCH FASTER.
2
5. 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. (5 points)
COESITE AND/OR STISHOVITE, HIGH-PRESSURE POLYMORPHS OF SILICA,
ARE THE CHARACTERISTIC MINERALS. AMORPHOUS GLASS, PRODUCED
BY IMPACT MELTING, IS OFTEN PRESENT. SHOCKED QUARTZ,
CHARACTERIZED BY THE PRESENCE OF SHOCK LAMALLAE, AND SHATTER
CONES ARE OFTEN SEEN.
5
6. 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? Why or why not? ( 2 points)
PROBABLY NOT. PLANAR ARRAYS ARE USUALLY FORMED BY
POST-METAMORPHIC FLUIDS SEEPING INTO THE ROCK ALONG CRACKS
13
23
7. What type of stress is produced by tectonic forces? What are three sub-categories of this type
of stress? (4 points)
Deviatoric stress
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
AVE A GREAT SUMMER AND ENJOY
SFC IF YOU ARE GOING ON IT.
IT'S BEEN FUN!
14