Metamorphism Agents, Fluids & Index Minerals

Where do most metamorphic rocks form?

between a few and many kilometers beneath Earth's surface

How do metamorphic rocks reach Earth's surface?

through removal of overlying rocks

Which two rock types would you expect to see sitting next to each other after a very long period characterized by only uplift and erosion?

metamorphic and sedimentary rocks

Could metamorphic rocks reach the surface of a planet without rock-uplifting processes?

No, metamorphic rocks must be uplifted and exposed by erosion.

The metamorphic grade refers to ________.

the degree to which the parent rock changes during metamorphism

Which of the following best describes the difference between differential stress and confining pressure?

In differential stress, the stresses on the sides are greater than the force of gravity. Stresses are the same on all sides for confining pressure.

Which of the following describes the orientation of the long axes of rocks and mineral grains in relationship to the stress applied?

Mineral grains are oriented parallel to the direction of the weakest stress applied.

The long axis of a rock is parallel to the direction of the weakest stress applied.

What are the four agents that drive metamorphism?

directional stress, pressure, heat, and chemically active fluids

What is the most important agent of metamorphism, and why?

Heat is the most important agent of metamorphism because it provides the energy necessary for chemical reactions to occur within the rock.

What role do chemically active fluids play in metamorphism?

Chemically active fluids can bring new atoms into the rock or take atoms out of the rock, thus altering the rock's composition.

Which of the following is not one of the agents of metamorphism?

calcium-rich liquids

During metamorphism, what is the major effect of chemically active fluids?

They aid in the movement of dissolved silicate constituents and facilitate growth of the mineral grains.

What are the processes by which grains in a rock can undergo foliation? Select all that apply

by the rotation of platy minerals

by recrystallizing into new minerals

by the flattening of spherical mineral grains

How do slaty cleavage, schistosity, and gneissic textures differ from each other?

These textures differ in that rocks with slaty cleavage break across their layers; rocks with schistosity exhibit layered structures of thin, platy minerals; and rocks with gneissic texture have a solid, banded appearance.

Which of the following metamorphic rocks are foliated? Choose all that apply.

gneiss, phyllite

Metamorphic rocks that contain large crystals embedded in a finer grained matrix have a ________ texture.

porphyroblastic

Which of the following is an example of a metamorphic rock with a nonfoliated texture?

marble

Examine the words and/or phrases below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.

schistosity

slaty cleavage

porphyroblastic

gneissic

porphyroblastic

Examine the words and/or phrases below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.

Examine the words and/or phrases below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.

pressurere

crystallization

chemical fluids

time

time

Which of the following statements concerning slate is NOT true?

It has abundant, coarse-grained mica.

Which of the statements below describes the appearance of gneiss and explains how it forms?

Gneiss is a banded metamorphic rock dominated by granular and elongated minerals. It often forms as a result of the high-grade metamorphism of shale, during which the rock's light and dark components separate.

Describe granite, schist, phyllite, and slate in terms of texture and grain size.

All four rocks are foliated, with slate having the smallest mineral grains, phyllite having the second smallest mineral grains, schist having the second largest mineral grains, and gneiss having the largest mineral grains.

Which of the following metamorphic rocks are nonfoliated? Choose all that apply.

quartzite

anthracite

Which rock has the finest grain size?

Slate

Foliation in metamorphic rocks is mainly evident in the parallel alignment of certain mineral grains. What are they?

Micas

Examine the words and/or phrases below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.

Examine the words and/or phrases below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.

phyllite

slate

marble

schist

Marble

What foliated, metamorphic rock is texturally intermediate between slate and schist?

Phyllite

Graphite is identified in a particular schist. Which one of the following conclusions is justified?

The pre-metamorphic rock was a shale or mudstone containing organic matter.

Amphibolite is a foliated metamorphic rock composed principally of hornblende and plagioclase. It forms ________.

by regional metamorphism of volcanic rocks such as basalt

________ is a nonfoliated rock formed by contact metamorphism of a shale or mudstone.

Hornfels

Which of the following factors describes the conditions at a zone where contact metamorphism is occurring?

Low pressure, high temperature

What is a metamorphic aureole?

a ring of metamorphic rocks adjacent to an igneous intrusion

How is quartz sandstone metamorphosed into quartzite during contact metamorphism?

Sand grains are fused together because of high temperatures.

Which of the following best describes confining pressure and the location in which it occurs?

moderate pressures at shallow depths

What is an aureole?

a discreet zone adjacent to the heat source in contact metamorphism

Which type of plate boundary is associated with regional metamorphism?

continental-continental convergent boundary

Which metamorphic feature is associated with contact metamorphism?

Aureole

Where would regional metamorphism occur? PLEASE SELECT ALL THAT APPLY.

Himalayas, Appalachian Mountains

Mylonites tend to form ________.

along fault zones

What term describes the zone of contact metamorphism surrounding an intrusive magma body?

Aureole

Which of the following environments would exhibit sheared and mechanically fragmented rocks?

fault movements at shallow depths

Which of the following forms at the highest grade of regional metamorphism?

Schist

What is the major source of heat for contact metamorphism?

Heat from a nearby magma body

Which option below orders the grades of metamorphism that would be encountered traveling eastward from Ohio toward the center of the Appalachian Mountains to the east?

low grade, then intermediate grade, then high grade

How do geologists use index minerals?

Index minerals are specific minerals that form at specific temperatures. The presence of these minerals within a metamorphic rock indicates the rock's metamorphic grade.

________ can provide good indication of the metamorphic environment in which a rock formed.

Index minerals

________ is thought to form by partial melting and in situ crystallization of the melted portion.

Migmatite