Choose the listing that shows the rocks in increasing degrees of metamorphism (from lower- to higher-grade).
metaconglomerate, gneiss with mica, gneiss without mica, migmatite.
(Metaconglomerate is barely metamorphosed; mica is an indicator of low-grade metamorphism; gneiss is a medium-to-high grade metamorphic rock, and migmatite is sufficiently high grade to h
What is the protolith of marble?
Limestone
(A protolith is the parent rock that is metamorphosed into a different rock; metamorphosed limestone is marble.)
Which of the following locations could not possibly be part of a shield?
Hawaii
(Shields are the oldest areas of Earth's surface; Hawaii is a recently formed hot spot island)
Identify the FALSE statement: A metamorphic rock
cannot be formed below 1200�C as all the rock minerals must melt.
(The upper limit of the metamorphic range is approximately 1200�C. Most metamorphism occurs between 200�C and 850�C.)
Identify the FALSE statement: Extremely high temperature of metamorphism
is necessary to form chlorite.
(Chlorite is produced during low-grade metamorphism and generally reacts with other minerals, and hence has disappeared before high metamorphic temperatures are reached.)
Mylonite
All the possible answers are correct...
(forms by recrystallization in a fault zone, is produced by shear stress on softened rock, forms due to dynamic metamorphism, has pronounced foliation parallel to the direction of the faulting)
Pick out the rock that is nonfoliated.
Hornfels
(Hornfels is nonfoliated rock because it was formed in the absence of differential stress.)
Identify the TRUE statement: Metasomatism
requires hot fluids in order to occur
(Requiring high pressure, but needing low temperatures applies to the creation of rare blueschist metamorphic rock in subduction zones, not to retrograde metamorphic rocks. )
Identify the FALSE statement: Metamorphic facies
are identical to metamorphic mineral assemblages.
(The different rocks within a single metamorphic facies do not all have the same mineral assemblages. The specific mineral assemblage present within a metamorphic facies depends upon the bulk chemistry of
Identify a TRUE statement (there is only one) about metamorphic rocks and their characteristic environments:
Slate, phyllite, schist, and gneiss are found in areas of continental collision.
(Gneiss, a foliated metamorphic rock, requires shearing stress to form; plutons don't cause shearing and they create nonfoliated rock. Mylonites form due to shearing stress a
Which of the following processes results in the exposure of deeply buried rocks at the Earth's surface?
exhumation
(Exhalation means, to breathe out, and diagenesis refers to post-decompositional alteration of sediment, and ductile deformation and metasomatism are both processes related within the realm of metamorphic or structural alteration of rock. Exhum
Which is NOT a common process by which metamorphic rocks are formed?
Schistosity
(Schistosity is not a process; it's the type of foliation in schists that results from the preferred orientation of large mica flakes.)
Mountain building due to convergent-margin tectonics and to continental collision
All the possible answers are correct...
(can metamorphose former surface rock by increased pressure, can send surface rock to great depths, can metamorphose former surface rock by proximity to magma, can metamorphose former surface rock by differential st
Recrystallization occurs because thermal energy causes atoms to vibrate rapidly, break existing chemical bonds, and migrate to new positions on the crystal lattice where they are more stable under the hotter conditions.
True
(This process doesn't change the identity or chemical composition of the mineral; it just produces larger crystals of the mineral.)
Roofers use the rock schist to shingle roofs because its foliation, called schistosity, causes it to break in convenient size.
False, they use slate!
(They use slate because cleavage causes it to break into suitable thicknesses for use as roof shingle.)
The mineral sillimanite indicates higher-grade metamorphism than staurolite.
True
(Sillimanite, staurolite, and kyanite are polymorphs of aluminum silicate, and each has a defined pressure-temperature field of stability. Sillimanite is stable at higher metamorphic grade than staurolite.)
Schist is a medium-grade foliated metamorphic rock that normally contains micas.
True
(Many different types of rocks are composed of atoms that can be metamorphosed into the mineral mica, which is a chief component of the metamorphic rock schist)
Which is NOT a cause of banding in gneiss?
preferential orientation
(Preferential orientation can impart foliation to a rock but cannot cause the compositional banding that defines a gneiss.)
Marble is a favorite material of sculptors because of its relative softness, and uniform texture.
True
(Marble is a favorite because it's uniform in texture, & can be worked with steel tools.)
Blueschist is a common metamorphic rock of continental shields.
False
(Blueschist is a rare, blue-colored rock formed under high-pressure, low-temperature conditions that are found in accretionary prisms adjacent to subduction zones.)
If the intrusion of magma (a pluton) melts mafic country rock, the resulting metamorphic rock is a schist or gneiss.
False
(If the intrusion of magma and formation of a pluton melts rock, you're no longer dealing with a metamorphic rock.)
Metamorphic aureoles typically contain nonfoliated rock like hornfels, because the pluton intrusion provides heat but not the shearing stress necessary for foliation.
True
(Differential stress is not associated with thermal metamorphism, such as that caused by an adjacent magma body.)
A supercritical fluid permeates rock very thoroughly because it has characteristics of both liquid and gas.
True
(The extremely high temperatures and pressures of supercritical fluids enable them to intrude like a gas and react with the material like a liquid.)
Which of the following is NOT required for pressure solution to occur?
greenschist-facies
(Pressure solution requires uneven stress, grain-to-grain contacts, and of course, the migration of atoms or ions. Pressure solution does not require greenschist-facies (low grade) metamorphism to occur.)
When geologists say metamorphic grade, they're referring to the general degree of metamorphism of a rock; when they say facies, they mean a subset of the broad temperature and pressure conditions in which metamorphism can occur.
True
(Metamorphic facies is a more specific descriptor of metamorphism than metamorphic grade. In contrast, metamorphic grade usually consists only of three simple categories: low, medium, and high.)
The sequence of increasing metamorphism of the protolith shale (a sedimentary rock) is slate, phyllite, schist, and gneiss.
True
(Metamorphism increases as temperature and pressure increase, and this is the sequence of rocks a shale would transform through, eventually becoming gneiss at very high temperature and pressure.)
Dynamothermal metamorphism (regional metamorphism) produces metamorphic rocks in the depths of mountain ranges, which erosion eventually exposes as "mountain roots" hundreds of kilometers wide and thousands of kilometers long.
True
(Continent-to-continent collision results in thickened crust over regions as extensive as the modern Himalayas. Physical weathering tears and wears the tops of such mountain ranges away and isostatic compensation lifts new material upwards. In this w
Dissolved ions freed during the process of metasomatism can precipitate to form mineral-filled cracks called veins.
True
(Hydrothermal fluids dissolve the ions, which are then free to relocate either in veins in the Earth or on its surface.)
Contact metamorphism occurs when
a mass of rock is affected by the heat of a magma.
(Think of contact metamorphism as what happens if you accidentally touch a very hot stove surface�your skin is altered by a transient (rapidly passing) rise in temperature)
Which process would you most expect during hydrothermal metamorphism near a mid-ocean ridge?
Metasomatism
(Metasomatism is the alteration of a rock's composition due to the interaction with very hot aqueous solutions, i.e., hydrothermal solution.)