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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? 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? 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 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?

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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 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?

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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? 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? 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? 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? 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: 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? 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

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• 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.

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• 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 chracteristic mineral assemblages.

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• 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

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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? 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 low-temperature 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? 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.