Metamorphism

Recrystallization of spherical minerals to create layers parallel to the direction of greatest stress

Which of the following is not an example of foliation?

Gneissic rocks undergo partial melting, which melts quartz and feldspar crystals and leaves biotite and amphibole behind. When the rock cools, light bands in the rock will be composed of igneous materials, and dark bands will consist of unmelted metamorphic material. They are not easily placed in any of the three rock groups because they represent a transitional stage, containing both igneous crystals and metamorphic crystals.

Explain how migmatites form. Why are they difficult to fit into any of the three basic rock types?

FALSE

Foliated textures are primarily the result of heat. Nonfoliated textures are primarily the result of directed pressure.

Their chemical composition will be nearly the same.

Generally speaking, how does the chemical composition of most metamorphic rocks compare to that of the parent rock?

A large, fast-moving body such as a meteorite will impact the Earth at a high velocity, quickly creating a high-pressure, high-temperature environment. The energy of the impact will be transformed into heat energy and shock waves, pulverizing and melting the rock.

How can a meteorite impact metamorphose a rock? What temperature/pressure conditions will be present?

Physical rotation of platy minerals will contribute most to the development of foliation

Low-grade metamorphism

Marble reacts with HCl, while quartzite will not. Quartzite will scratch glass or steel, while marble will not.

Marble and quartzite can be similar in appearance. Name two simple ID techniques that can be used to differentiate between the two.

9) A 10) D 11) B 12) C 13) E

Match the index mineral with the correct metamorphic grade(s). For these purposes, please remember that for a mineral to be part of two metamorphic grades, it should make up at least one-third of both grades. A) Low grade B) Low to medium grade C) Medium to high D) Medium grade E) High grade 9) Chlorite 10) Staurolite 11) Muscovite 12) Garnet 13) Sillimanite

1) B 2) A 3) C 4) B

Match the metamorphic rock to the metamorphic grade. (Note: Some answers may be used more than once.) A) High-grade metamorphism B) Low-grade metamorphism C) Medium-grade metamorphism 1) Slate 2) Gneiss 3) Schist 4) Phyllite

basaltic

Metamorphic facies derive their names from those metamorphic rocks specifically formed from a ________ parent.

the process by which a rock changes form or mineral content as a result of environmental changes such as heat and pressure.

Metamorphism

TRUE

Metamorphism ends when the rock begins to melt

Shale, quartz sandstone, and limestone

Most metamorphic rocks near the Earth's surface are derived from three common sedimentary rocks. Which three?

Quartzite, marble, and hornfels

Name three rocks that are produced by contact metamorphism.

Slate has very flat layers and is dull in appearance. Phyllite has wavy layers and has a sheen.

Slate and phyllite are similar in appearance. How can the foliation and the shine be used to tell them apart?

Which of the following materials is most closely associated with shock metamorphism and meteorite impact sites?

Tektites

TRUE

The geothermal gradient represents a decrease in interior temperature with decreasing distance from the surface.

Gneissic banding is the highest degree of foliation that can form before the rock begins to melt. It forms in high-grade metamorphic conditions and when minerals segregate into separate layers, which often gives the appearance of alternating light and dark layers. This effect differs from color banding, which has alternating light and dark layers but little difference in mineral crystals between the layers.

What is gneissic banding, how does it form, and how does it compare to the color banding that is often found in marble?

25°C per km

What is the average increase in temperature along the geothermal gradient in the upper crust?

a rock that was altered by metamorphism.

What is the definition of a parent rock?

The change in chemical composition because hot fluids are bringing or removing ions

What is the definition of metasomatism?

13 km

What is the minimum depth at which subduction zone metamorphism will occur?

Heat

What is the most important factor driving metamorphism?

Quartzite

What is the name of this rock? (Hint: It can scratch glass.)

Sandstone

What is the parent rock of quartzite.

0-400°C

What is the temperature range over which hydrothermal metamorphism will occur?

An assenblage of minerals that form in very similar metamorphic environment

What its a metamorphic facies?

Compression

What kind of force will create foliation in metamorphic rocks?

Regional

What kind of metamorphism will occur if the environmental conditions are 400°C and 5 kilobars?

Contact

What kind of metamorphism will occur if the temperature is 800°C and the depth of metamorphism is 7 km?

Low temperature and low pressure

What kind of temperature and pressure conditions will exist in a burial metamorphism environment?

Low temperature and high pressure

What kind of temperature and pressure conditions will exist in a subduction zone metamorphic environment?

Heat allows individual ions to migrate more freely between sites in the crystalline structure or migrate into or out of rocks. In the process, new mineral grains will form that are larger than the original grains.

What role does heat play in creating new minerals or new crystalline structures in metamorphic rocks?

Heat

Which agent of metamorphism was primarily responsible for generating the rock in the image in the previous question?

Differential stress

Which kind of stress (confining pressure or differential stress) is responsible for creating the texture visible in this rock?

Slate

Which low-grade metamorphic rock displays thin, parallel layers and contains very fine grains of mica?

Eclogite

Which of the following as a metamorphic facies?

Shale, granite, schist, and phyllite

Which of the following can be a parent rock for gneiss?

Great depth and high temperatures

Which of the following environments would most likely produce metamorphism in fault zones?

Slate, phyllite, schist, gneiss.

Which of the following lists of metamorphic rocks places the rocks in order from lowest metamorphic grade to highest?

Gneiss

Which of the following rocks represents the highest grade of metamorphism?

Chlorite, epidote and serpentine

Which of these minerals assemblage is characteristic of a greenschist facies?

Contact

Which style of metamorphism will be generated by a magma pluton?

Because quartz is stable over a wide range of metamorphic settings

Why is quartz a bad mineral to use to determine a metamorphic environment?

Because the main agent of metamorphism is heat, which will result in intergrown crystals

Why will metamorphic rocks found in a contact metamorphism aureole be nonfoliated?

This manuscript should not be approved for publication because the temperature and pressure conditions cited are not found in nature.

You have been asked to review a manuscript that has been submitted for publication in a professional journal. The area of interest in this article is an amphibolite exposed along the Chippewa River at Jim Falls, Wisconsin. The researchers state that the amphibolite is believed to have been altered 2.6 billion years ago by tectonic pressures of 14 kilobars and temperatures of 190°C. Should you approve this manuscript for publication? Why or why not?

Differential stress

________ can produce intricately folded rocks.

Hydrothermal

________ metamorphism is responsible for the emplacement of metallic ore veins.

Contact

________ metamorphism will occur when high-speed projectiles strike the Earth's surface.

occurs in regions where massive amounts of sedimentary to volcanic materials accumulate in a subsiding basin, pushing older rocks further into interior.

burial metamorphism

Which of the following is not an environment of metamorphism? A) Contact with a hot magma body B) Hot fluids coming off a diaper C) Slow cooling of a magma D) High pressure in a subduction zone

c) Slow cooling of a magma

A change in the texture, structure, or chemical composition of a rock due to contact with magma.

contact metamorphism

stress applied unequally in different directions

differential stress

high temperature and pressure

high grade

Minerals in metamorphic rocks that help scientists determine the average temperature and pressure the metamorphic rock was in.

index minerals

minerals used to estimate the temperature, depth, and pressure at which a rock undergoes metamorphism

index minerals

convergent

Along which type of tectonic boundary will greenschists and blueschist form

West and east

Assume that this foliated rock is oriented so that north is at the top of the image. From which compass directions is the greatest differential stress coming?

500°C and 4 kilobars

At what temperature and pressure would kyanite, sillimanite, and andalusite form simultaneously?

A metamorphic rock formed under high pressures and moderate temperatures, often containing glaucophane, a blue amphibole

Blueschist

Yes, because such features can withstand low temperatures and pressures but will be destroyed in higher metamorphic grades.

Can parent rock features such as sedimentary structures and fossils survive low-grade metamorphism?

The degree to which a parent rock changes during metamorphism.

Define metamorphic grade.

Heat, pressure, differential stress, and chemically active fluids

What are the four agents of metamorphism?

Foliated and nonfoliated

What are the two main categories of metamorphic texture?

granulite

What facies is associated with a high-pressure, low-temperature environment?

Water

What fluid is generally responsible for metasomatism?

parallel alignment of minerals

What is foliation?

Confining pressure on metamorphic rocks by applying pressure equally in all directions will collapse any open spaces between mineral grains to produce a more dense rock. An environmental example would be younger overlying materials burying sedimentary rocks and forcing them deeper into the interior. Compressional stress metamorphoses rocks by applying pressure that is greater in one direction and weaker in another. (For example, the horizontal pressure is greater than the vertical pressure.) This will cause the mineral crystals to elongate or reorient so that the crystal's long axis is perpendicular to the direction of highest pressure. An environment that would create such a scenario can include a convergent plate boundary.

Compare and contrast confining pressure and compressional stress relating to metamorphic rocks. What will happen to the mineral crystals in each situation? Also, provide examples of geologic environments where such pressure would be the main agent of metamorphism.

If the igneous structure is small (e.g. a dike), then the aureole will also be small, only a few centimeters in thickness. However, larger igneous bodies have more heat that they will release over a longer period of time. This means that the aureole will be more extensive (several kilometers for those around batholiths) and have zones of metamorphism.

Compare and contrast how the aureole of contact metamorphism will change in thickness depending on the intrusive igneous structure.

Tectonic boundary that is associated with regional metamorphism?

Convergert

Muscovite

If clay minerals in a sedimentary rock were buried at a depth where subsurface temperatures exceeded 200c, which common metamorphic mineral would they become?

Kyanite

If shale is buried to a depth of 20 km and the temperature is raised to 450°C, which mineral would form according to the image above?

Along the axis of a mid-ocean ridge system

In which geologic setting is the most widespread occurrence of hydrothermal metamorphism found?

confining pressure

Olivine can be converted to spinel through ________.

FALSE

Sedimentary rocks are always the parent rocks for metamorphic rocks.

15) C 16) D 17) A 18) B

Using the images above, select the correct name for each metamorphic rock and match it with the correct image. Then, select the correct metamorphic grade for each rock. A) Schist, medium B) Gneiss, high C) Slate, low D) Phyllite, low 15) A 16) B 17) C 18) D

low temperature and pressure

low grade

intermediate pressures and temperatures

mountain belt metamorphism

widespread type of metamorphism typically associated with mountain building.

regional metamorphism

Recrystallization

the process by which new mineral grains larger than the original mineral grains form as a result of metamorphic heat