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Transcript
Metamorphic Petrology Review
Spring 2015
1
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
2
1. The starting material from which a reaction or
recrystallization begins is called what?
2. What does SCMR stand for?
3. What organization established SCMR?
4. Which of the following minerals might be used to
characterize the onset of metamorphism?
A. Garnet
B. Zoisite
C. Omphacite
D. Prehnite
3
1. Other minerals that characterize the onset
of metamorphism are ?
2. Under what two conditions does intense
heat promote recrystallization?
3. What is a mineralizer?
4. What is the most effective mineralizer?
5. Name two other common mineralizers in
rocks?
4
1.
2.
3.
4.
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?
5
1. What conditions of σ1, σ2, and σ3 are required
to produce each of the following?
a) Foliation, no lineation
b) Lineation, no foliation
c) Both foliation and lineation
2. (T-F) New minerals will growth during
deformation, parallel to σ1.
3. (T-F) The fluid phase associated with
metamorphic reactions is a liquid.
6
1. 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?
2. What formula can be used to calculate
lithostatic pressure in near-surface
environments?
7
1. 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?
2. Name six sources of metamorphic fluids.
3. (T-F) The effects of contact metamorphism
are most evident in shallow, low-pressure
environments.
8
1. Are relict structures preserved in hornfels and
granofels?
2. What is the difference between a hornfels and a
granofels?
3. What is pyrometamorphism? How might it occur?
4. Where would orogenic metamorphism occur?
5. (T-F) Many orogenic episodes produce repeated
episodes of deformation and metamorphism, leaving
a polymetamorphic imprint
9
1. Describe the agents at work in burial metamorphism
2. 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?
3. What is a major difference between orogenic
metamorphism and burial metamorphism?
10
1. What are the principal agents of metamorphism
involved with ocean-floor metamorphism?
2. Ocean-floor metamorphism involves considerable
chemical replacement. What elements are
principally involved? What is the source of the new
ions?
3. Basalt, altered by ocean-floor metamorphism, often
retains the structures of basalt, including vesicles
and pillow structures. The altered rock is called
what?
11
1. 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?
2. What is the agent associated with fault-zone
metamorphism?
12
1. 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
2. The terms high-stress metamorphism and
dynamic metamorphism are used for two
distinct types of metamorphism. What are
they?
13
1. What is the difference between fault gouge and fault
breccia?
2. (T-F) All minerals show the transition from brittle to
ductile under very similar conditions.
3. What two minerals are considered characteristic of
impact metamorphism? What other material is often
found in impact zones?
4. Describe two other features that are commonly
associated with impacts.
5. Metamorphism produced by increasing temperature
and pressure is called _____________________
metamorphism.
14
1. Metamorphism produced by decreasing temperature
and pressure is called _____________________
metamorphism.
2. During most types of metamorphism, equilibrium is
thought to be obtained, and to prevail during ongoing metamorphism. This idea is given what name?
3. (T-F) Prograde metamorphic reactions are
exothermic.
4. Retrograde reaction may not be possible after
prograde metamorphism has occurred. Why?
15
1. Many of the reactions used for geothermobarometry
are exchange reactions. Why?
2. 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.
3. The term psammitic refers to what?
4. 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.
16
1. Did Barrow find a greater change in the sandstones
or the pelitic rocks he studied?
2. 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.
3. Who introduced the term isograd for that boundary
that separates Barrovian zones?
17
1. (T-F) It is possible for an index mineral to be
present in a zone of higher grade than its own.
2. (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.
3. (T-F) When andalusite is present, the pressure at the
time of formation exceeded 0.4 GPa.
4. (T-F) Cordierite has a large molar volume, which
indicates it is stable at low pressures.
18
1. (T-F) At very low metamorphic grade, reaction rates
are slow.
2. (T-F) Ca-bearing minerals, like laumonite, prehnite,
and pumpellyite are stable in water-rich, carbonatefree fluids.
3. The Sanbagawa belt lies nearer the subduction zone
than the Ryoke belt. Which belt is richer in alkaline
elements?
4. 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?
19
1. Among petrologists, the Crestmore Quarry in California
is very famous. For what is it famous? How did it form?
2. (T-F) Rock materials formed under high-strain
conditions may be either cohesive or non-cohesive.
3. Non-foliated cohesive rocks include microbreccias and
cataclasites. How do they differ?
4. Phyllonites are foliated cohesive rocks rich in what
mineral?
5. A cohesive high-strain rock that has undergone
significant recrystallization is known as what?
6. Under extreme conditions, frictional heating will
produce partial melting, creating glass. Rocks with
glassy seams are called what?
20
1. (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.
2. Who first formulated the idea of metamorphic
facies?
A. C.E. Tilley
B. Pentii Eskola
C. George Barrow
D. Alfred Harker
3. (T-F) The original facies classification was based
primarily on metamorphosed mafic rocks.
21
1. What important contribution did Viktor
Goldschmidt make to the study of equilibrium
mineral assemblages?
2. In metamorphic rocks, a
is
a set of repeatedly associated mineral assemblages.
3. 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
22
1. 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
2. Who proposed the addition the zeolite and prehnitepumpellyite facies to Eskola’s original set of five
facies?
A. Eskola
B. Coombs
C. Fyfe
D. All of the above
23
1. (T-F) There is little difference in mafic rock facies that
develop at low, medium, or even high pressure.
2. Using Yardley’s classification, identify the facies associated
with each group:
A. High-pressure
B. Medium-pressure
C. Low-pressure
D. Low-grade
3. In metamorphic assemblages, the symbol ± is short for what
phrase?
4. What names did Miyashiro give to his final compilation of
three baric series?
24
1. 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
2. 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
25
1. 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
2. (T-F) The high P/T baric series is characteristic of below
normal geothermal gradients, such as in subduction zones.
3. What is an immature graywacke?
4. (T-F) Ordinary prograde metamorphic reactions are common
in high-temperature mafic igneous rocks.
26
1. If water for hydration reactions were available in hightemperature mafic igneous rocks, would coarse-grained or
fine-grained rocks react faster? Why?
2. (T-F) Hydration reactions may release large quantities of
energy, significantly heating the rocks.
3. (T-F) If equilibrium is maintained, there is a correlation
between the An content of plagioclase and the temperature.
4. (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.
27
1. 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
2. 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
28
1. The transition from the greenschist to the
amphibolite facies involves two major
mineralogical changes. What are they?
2. (T-F) In a Barrovian sequence, oligoclase
appears before hornblende.
3. As grade increases, the color of hornblende
changes from green to brown. Why?
4. Hydrous pelitic and quartzo-feldspathic rocks
do not reach granulite grade. Why?
29
1. 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:
2. Granulites are thought to form in regions of
crustal thickening. Why?
30
1. 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
2. Coleman first described three distinct
petrologic settings eclogites are associated
with in 1965. What were his three settings?
31
1.
What temperature range is a medium
temperature eclogite associated with?
A. 200 - 400°C
B. 450 - 550°C
C. 550 - 900°C
D. 900 - 1600°C
2.
(T-F) Eclogites span a greater temperature
range than any other facies.
3.
(T-F) Ecolgites associated with xenoliths in
kimberlites or basalts belong to the lowtemperature group.
32
1. Eclogites associated with migmatitic gneisses are
usually associated with which temperature group?
A. Low
B. Medium
C. High
D. Any of the above
2. 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.
33
1. Describe three ways we can gain information about
P-T-t paths.
2. (T-F) Greenschist-amphibolite facies, such as those
of Western North Carolina, require an average
continental crustal geotherm to form.
3. Where does the extra heat come from?
4. Which path is associated with orogenic belt crustal
thickening?
A. a
B. b
C. c
D. All of the above
34
35
1. What does path “b” represent?
2. (T-F) Path “c” is common in high-grade
gneiss, and granulite facies terraines.
3. What produces path “c”?
4. Retrograde reactions, where water is lacking,
are slow. Granulite facies rocks may show
retrograde metamorphism. Why, since these
rocks are usually anhydrous?
5. (T-F) Counterclockwise P-T-t paths are found
only in granulite facies rocks.
36
1. P-T-t diagrams are deceptive in one very important
respect. What is it?
2. (T-F) For most paths, Pmax and Tmax occur at the
same time.
3. For path “a”, do pressure and temperature increase
together?
4. (T-F) Metamorphic grade is most closely related to
Pmax.
5. (T-F) Blueschist preservation, rather than blueschist
generation, may be more important in determining
whether blueschist rocks are seen in a region.
37
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