Transcript Petrology Lecture 9 Review - FAU

Metamorphic Petrology Review
Spring 2011
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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
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• 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?
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Garnet
Zoisite
Omphacite
Prehnite
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• 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?
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• 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 temperture.
• What type of stress is produced by
tectonic forces?
• What are three sub-categories of this type
of stress?
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• 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.
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• 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?
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• Below a certain depth, around 10 km, the
pressure at the point of mineral contact, Plith,
will be very much greater then 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.
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• 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
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• 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 metamorphiosm?
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• 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?
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• 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?
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• Which of the following terms is used in place
of fault-zone metamorphism?
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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?
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• 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.
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• 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?
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• 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.
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• 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?
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• (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) Whan 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.
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• (T-F) At very low metamorphic grade, reaction
rates are slow.
• (T-F) Ca-bearing minerals, like laumonite,
prehnite, and pumpellyite are stable in waterrich, 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?
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• 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 noncohesive.
• 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?
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• (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?
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A. C.E. Tilley
B. Pentii Eskola
C. George Barrow
D. Alfred Harker
 (T-F) The original facies calssification was based
primarily on metamorphosed mafic rocks.
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• 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?
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A. Escola
B. Coombs
C. Fyfe
D. Goldschmidt
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• Who proposed the addition of the ganulite,
epidote amphibolite, and glaucophane schist
facies to Eskola’s original set of five facies?
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A. Escola
B. Coombs
C. Fyfe
D. Goldschmidt
• Who proposed the addition the zeolite and
prehnite-pumpellyite facies to Eskola’s original
set of five facies?
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A. Escola
B. Coombs
C. Fyfe
D. All of the above
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• (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:
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High-pressure
Medium-pressure
Low-pressure
Low-grade
 In metamorphic assmblages, the symbol ± is short for
what phrase?
 What names did Miyashiro give to his final
compilation of three baric series?
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• Where might a low P/T baric series be found?
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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?
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A. High P/T
B. Medium P/T
C. Low P/T
D. May be any of the above
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• The Buchan type of metamorphic trajectory is
characteristic of which baric series?
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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.
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• If water for hydration reactions were available in
high-temperature mafic igneous rocks, would coarsegrained 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 chracteristic mineral assemblages.
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• At the high temperature end of the prehnitepumpellyite facies, prehnite may break down to yield
what mineral?
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A. Actinolite
B. Hornblende
C. Enstatite
D. Forsterite
• The most common regional metamorphic rocks are
characteristic of what baric series?
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A. High P/T
B. Medium P/T
C. Low P/T
D. May be any of the above
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• 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 fro green to brown. Why?
• Hydrous pelitic and quartzo-feldspathic rocks
do not reach granulite grade. Why?
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• 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?
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• As pressure increases, amphibolite or granulite
facies rocks transform to eclogites. It is the
initial breakdown of which mineral that marks
this transition?
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A. Enstatite
B. Hornblende
C. Plagioclase
D. Garnet
 Coleman first described three distinct
petrologic settings eclogites are associated
with in 1965. What were his three settings?
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• 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
• (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 lowtemperature group.
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• 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.
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• 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 orogrenic belt crustal
thickening?
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A. a
B. b
C. c
D. All of the above
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• 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) Counterclockwide P-T-t paths are found
only in granulite facies rocks.
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• P-T-t diagrams are deceptive in one very important
respect. Whit 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.
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