METAMORPHISM AND METAMORPHIC 8
ROCKS
INTRODUCTION
Metamorphism and Metamorphic Rocks
CHAPTER OUTLINE
1.
2.
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3.
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4.
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schist
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5.
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6.
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7.
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LEARNING OBJECTIVES/FOCUS ON CONCEPTS
8.1 Compare and contrast
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8.3 Explain
8.5 Write a statement
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8.7 Describe
TEACHING STRATEGIES
Clicker Questions:
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Muddiest Point:
A. Metamorphic Rock Identification
B. Metamorphic Facies
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TEACHER RESOURCES
Web Resources:
About Metamorphic Rocks
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Imagery and Animations:
Images
ANSWERS TO QUESTIONS IN THE CHAPTER:
CONCEPT CHECKS
8.1 WHAT IS METAMORPHISM?
1. Metamorphism is a change in mineralogy, texture, and sometimes chemical composition of a
pre-existing rock.
2. A rock metamorphoses when it is exposed to conditions different from those in which it formed.
3. Metamorphic grade is the degree of metamorphism a rock undergoes; low-grade
metamorphism involves low temperatures and low pressures, high-grade metamorphism
8.2 WHAT DRIVES METAMORPHISM
1. The four agents that drive metamorphism are heat, confining pressure, differential pressure,
and chemically active fluids.
2. Heat provides the energy needed to drive the chemical reactions that result in the
4. Chemically active fluids enhance metamorphism because they transport ions from one site to
5. Parent material is the rock from which a metamorphic rock originates. The resulting
8.3 METAMORPHIC TEXTURES
2. Slaty cleavage is the tendency of slate to split along parallel planes. Schistosity is the strong
foliation in metamorphic rocks created by aligned mica and/or chlorite grains; aligned
3. Preferred orientation, or foliation, is the result of: (1) rotation of platy or elongated minerals
into new orientations by the differential stress of metamorphism, (2) recrystallization of new
4. Nonfoliated textures are those that do not display layering or banding. These occur where
deformation is minimal, or where the parent rocks are composed of equidimensional crystals.
8.4 COMMON METAMORPHIC ROCKS
1. Slate forms at lower grades of metamorphism and exhibits rock cleavage, but no visible grains,
2. A mica schist is a metamorphic rock composed primarily of mica with a schist texture.
3. Gneiss is characterized by alternating bands of light and dark silicate minerals. Gneiss forms in
4. Slate is a fine-grained metamorphic rock composed of very small chlorite and mica flakes;
slate breaks into flat slabs (slaty cleavage) with smooth, dull surfaces. Phyllite is fine grained,
5. Marble and quartzite are both nonfoliated metamorphic rocks. Marble is a softer rock
8.5 METAMORPHIC ENVIRONMENTS
1. Compressional stresses, those that act uniformly in all directions, are found in areas of burial
2. Contact metamorphism bakes rocks surrounding an intrusive igneous body. Metamorphic
3. An aureole is the area around an intrusive igneous body that is metamorphosed by the heat of
4. Water is the agent of metamorphism in hydrothermal metamorphism. This water may come
5. Subduction zone metamorphism occurs where oceanic rocks and sediment are carried to great
6. Regional metamorphism is associated with continental collisional plate boundaries. Here, rock
7. Because regional metamorphism is large scale and created by high pressures, this form of
8.6 METAMORPHIC ZONES
1. In Ohio, we see relatively flat-lying layers of sedimentary shale. As we move eastward, we
2. Index minerals give geologists clues about the intensity of metamorphism that a rock
experienced. Different minerals form under different temperature and pressure regimes, and
3. Migmatites represent a transitional rock type between metamorphic and igneous rocks. As
gneiss undergoes continued extreme metamorphism, its light-colored silicate minerals may
8.7 INTERPRETING METAMORPHIC ENVIRONMENTS
1. Metamorphic facies are certain assemblages of minerals in a metamorphic rock characteristic
of environments of pressure and temperature. Rocks that belong to the same metamorphic
2. Temperature and pressure within Earth vary to form different metamorphic environments.
For example, areas of contact metamorphism near the surface experience relatively low
3. Figure 8.32 tells us that the blueschist facies represents rocks that were formed under
4. Hornfels facies, according to Figure 8.32, form at low pressures but relatively high
temperatures. This would be characteristic of contact metamorphism where a high-
EYE ON EARTH
EOE #1 PURGATORY CHASM, NEWPORT, RHODE ISLAND
1. This rock is likely a metaconglomerate.
2. Because the grains are elongated from left to right in the image, the maximum directional
EOE #2 METAMORPHIC ROCK IN THE SOUTHERN ALPS
1. These rocks do display foliation because we see a clear banding or layered appearance as
2. These rocks would likely be called slates or schists due to their tendency to break along
EOE #3 JOSHUA TREE NATIONAL PARK OUTCROP
1. The dark-colored metamorphic rocks in this area were likely formed from contact
2. Here, an igneous intrusion entered the host rock (likely shale) and baked that rock under
low-grade heat and pressure conditions. This created an aureole of dark-colored igneous
EOE #4 MATTERHORN
2. The formation of the Matterhorn is likely a convergent, collisional plate boundary where
3. Gneiss is indicative of high-grade metamorphism (high temperature, high pressure), and
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GIVE IT SOME THOUGHT
1.
a. Marble
b. Fault breccia
2. Rock B is most likely from a metamorphic environment because we see wavy layers of light and
dark minerals, indicative of gneiss formation in high-directional stresses. Rock A is likely
3. As shale goes from low to high grade metamorphism, its minerals become larger and then
segregate into light and dark bands. At low temperatures and pressure, the clay minerals of the
4.
a. Schist indicates a fairly high-temperature, high-pressure environment of formation. This
suggests that these rocks were formed very deep in the crust, most likely in a regional
metamorphism environment such as that associated with mountain building. The rocks
5.
a. Conglomerates are composed of loosely cemented grains formed in a sedimentary
7.
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a. Along line A-B, metamorphic grade changes from low to intermediate to high and back to
8.
A. Igneous
9.
a. The black lines represent the relic bedding surfaces and the red lines represent the slaty
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