Geology Exam #2

500 degrees C and 4 kilobars

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

Assimilation occurs when magma that is injected into bedrock melts the rock directly surrounding it, incorporating it into the magma, whereas magma mixing occurs when two ascending bodies of magma join and mix together into a composition that is intermediate to the two original magmas.

Choose the statement that describes two processes that alter the composition of magma. Hint: one process of magma alteration involves two liquids, and the other process involved a liquid and a solid.

Biochemical rocks form from organisms that were once alive, such as limestone from marine shells, whereas inorganic chemical rocks form from non-biological processes, such as salt that is left behind when a lake evaporates.

Differentiate between the formation of biochemical rocks and the formation of inorganic chemical rocks. Hint: Whether biochemical or inorganic, all chemical rocks form from ions that have been dissolved in and carried by water.

Felsic; crystal size

Fill in the blanks in this sentence using the terms below: Granite and rhyolite are both ___, but they differ in ___. Hint: Remember that the two main characteristics that are used to classify igneous rocks are by their textures and compositions.

Plagioclase feldspar and quartz; pyroxene and olivine

Fill in the blanks using the choices below: ___ are minerals typically found in igneous rocks that have a high silica content, whereas ___ are minerals that are typically found in igneous rocks with a low silica content. Hint: Remember that the color of an igneous rock is dependent of the minerals it contains. A light-colored rock results from light minerals, and a dark-colored rock results from dark minerals.

The partial melting of the ultramafic rock peridotite

How are basaltic magmas thought to be formed? Hint: Basalt is an igneous rock that has a high content of iron and magnesium. Which compositional category does this describe?

Chemical rocks are primarily identified based on their compositions, whereas detrital rocks are primarily identified based on their particle sizes.

How are chemical rocks identified, and how does this differ from how detrital rocks are identified? Hint: One of these groups describes rocks that form in situ, whereas the other group describes rocks that form distantly from their compositions' original locations.

Unlike slate, which has a flat surface, phyllite has a glossy sheen and a wavy surface.

How can slate and phyllite be differentiated? Hint: The grain sizes in slate are much smaller than the grain sizes in phyllite. As smaller grains can pack together more closely than larger grains, how might this affect the appearances of these two rocks?

When carbon dioxide in the atmosphere combines with water, it creates carbonic acid, which precipitates and chemically weathers the rocks on Earth. The result of this weathering is bicarbonate, which ultimately ends up in the oceans and is used by marine organisms to make their shells. When these organisms die, their skeletons settle to the ocean floor and eventually become a rock layer containing the carbon dioxide.

How do chemical weathering and the formation of biochemical sediment remove carbon from the atmosphere and store it in the geosphere? Hint: Carbonic acid is an important catalyst in this process.

Large crystals in pegmatites are the result of high percentage of the melt being composed of water, carbon dioxide, and other materials. These materials enhance ion migration, allowing the crystals to grow larger than usual.

How do crystals in pegmatite grow so large? Hint: The large crystals in pegmatites are made of minerals; in turn, minerals are made of ions. What factor(s) might help add a high quantity of mineral ions to a pegmatite crystal?

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.

How do geologists use "index minerals"? Hint: Index minerals in metamorphic rocks are particularly useful in differentiating between zones of regional metamorphism.

After the earliest formed minerals have settled, the resulting magma will be more felsic than the original magma.

How do the crystallization and settling of the earliest formed minerals affect the composition of the remaining magma? Hint: the order in which minerals crystallize is dependent on their chemical composition, a correlation that is shown in Bowen's reaction series.

Tuff and volcanic breccia do not consistently belong to a single compositional category, unlike granite which is always felsic, and basalt, which is always mafic.

In what way do tuff and volcanic breccia differ from other igneous rocks such as granite and basalt? Hint: Both tuff and volcanic breccia form as a result of volcanic eruptions, however, their individual textures differ in particle size.

At a mid-oceanic ridge and at an oceanic-continental convergent boundary

In which two plate tectonic settings would one expect magma to be generated? Hint: remember the three basic ways in which magma can be generated: by a decrease in pressure, by the lowering of temperature due to the addition of water, and by the heating and melting of crustal rocks.

regional metamorphism

In which type of metamorphism does compressional stress play a major role? Hint: In what type of environment do two large pieces of Earth move toward each other, ultimately colliding and crumpling up to form mountains? What type of metamorphism occurs in this environment?

Slate: Low-grade metamorphism Gneiss: High-grade metamorphism Schist- Medium-grade metamorphism Phyllite: Low-grade metamorphism

Match the metamorphic rock to the metamorphic grade. Drag the terms on the left to the appropriate blanks on the right. (Terms can be used more than once.)

Sandstone: Detrital Chert: Chemical Shale: Detrital Bituminous Coal: Organic Rock Salt: Chemical Coquina: Chemical

Match the rock with the appropriate category of sedimentary rock. Drag the terms on the left to the appropriate blanks on the right. (Terms can be used more than once.)

Quartzite, marble, and hornfels

Name three rocks that are produced by contact metamorphism.

False

Particle SHAPE is the primary basis for distinguishing among various detrital sedimentary rocks.

iron, magnesium, feldspars, and silica

Peridotite that undergoes partial melting will create a melt enriched in ___.

Stocks

Plutonic bodies that have a surface exposure less than 100 km^2 are called ___.

Dikes are discordant igneous intrusions; sills are concordant igneous intrusions; both are tabular.

Select the correct description of dikes and sills. Hint: A discordant igneous body cuts across bedding surfaces in the country rock, whereas a concordant igneous body is found between bedding surfaces.

Intermediate

The partial melting of mafic rocks would produce what composition of magma?

The crustal rocks into which igneous bodies intrude

To what does the term "country rock" refer? Hint: Another term for "country rock" is "host rock".

-by recrystallizing into new minerals -by the rotation of platy minerals -by the flattening of spherical mineral grains

What are the processes by which grains in a rock can undergo foliation? PLEASE SELECT ALL THAT APPLY. Hint: The methods of foliation do not add or remove mineral grains from rocks but rather alter the grains within the rocks.

marine environments, such as deep ocean floors; continental environments, such as deserts; transitional environments, such as tidal flats

What are the three broad categories of sedimentary environments with an example of each? Hint: Instead of identifying environment types based on the presence or lack of water, consider if the environment occurs on continental crust, on ocean crust, or near their borders.

Travertine and oolitic limestone

What are two examples of inorganic limestone?

The rock began cooling under the Earth's surface, but then was moved to above the Earth's surface where it finished cooling.

What does a porphyritic texture indicate about the cooling history of an igneous rock? Hint: In a porphyritic rock, the phenocrysts solidify before the ground mass solidifies.

The order in which specific minerals cool and form within melted magma, from hottest to coolest.

What is Bowen's reaction series? Hint: Bowen's reaction series is in the order of first to last.

Mica refers to the rock's main composition (muscovite and biotite); schist refers to the rock's texture.

What is mica schist? Hint: Composition and texture are the two characteristics that are immediately used to describe rocks. Which of the terms in mica schist sounds like the name of a metamorphic rock texture?

Cross-bedding occurs when sediments are layered at an angled inclined to the horizontal, whereas graded bedding occurs when larger sediments are deposited at the bottom of the layer, gradually changing to fine sediments at the top.

What is the difference between cross-bedding and graded bedding? Hint: One of these features is the result of turbidity currents, whereas the other feature is the result of sand dunes.

13 km

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

Shale

What is the most common sedimentary rock?

A basaltic pond of magma becomes trapped below continental crust and partially melts this silica-rich crust into a granitic magma.

What is the process that is thought to generate most granitic magmas? Hint: Remember that granitic magma has a high silica content and a low iron content, basaltic magma has a high iron content and a low silica content, and andesitic magma is fairly balanced in its content of iron and silica.

Plants are the raw material for coal; to form coal plants must accumulate in oxygen deficient swamp water.

What is the raw material for coal, and how does it accumulate? Hint: Although there are many materials produced at different stages of coal production, the raw material for coal is in the very first stage of coal's formation.

Groundwater from the surface and fluids from magma plutons

What is the source of water for hydrothermal metamorphism?

0 to 400 degrees C

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

Low temperature and low pressure

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

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

What role do chemically active fluids play in metamorphism? Hint: Chemically active fluids differ from water in that they contain dissolved ions, which can contribute to the metamorphism of preexisting rock. Water alone cannot do this.

Differential stress

Which kind of stress (confining pressure or differential stress) is responsible for creating the texture visible in this rock? (Black and white stripes going vertically)

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.

Which of the below statements describes the appearance of gneiss and explains how it forms? Hint: Composition and texture are the two characteristics that are immediately used to describe rocks. How do these qualities relate to the formation history of a metamorphic rock?

granitic, andesitic, basaltic, ultramafic

Which of the choices below lists the four basic compositional groups of igneous rocks, ranging from the highest silica content to the lowest silica content? Hint: Three of the igneous composition group names have the synonyms intermediate, mafic, and felsic.

The burning of fossil fuels (e.g., coal) releases carbon dioxide directly into the atmosphere.

Which of the examples below shows how carbon moves from the geosphere directly to the atmosphere? Hint: The correct answer describes the direct path of carbon from the land to the atmospheres without any additional steps in between.

Shale, granite, schist, and phyllite

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

Dorite is intermediate with a phaneritic texture; rhyolite is felsic with an aphanitic texture; basalt porphyry is mafic with a porphyritic texture.

Which of the following choices classifies the three listed rocks by composition and texture? Hint: For each rock, please determine its crystal size and its relative content of silica.

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

Which of the following is not an example of foliation?

Wind

Which of the following methods of transportation will result in the best degree of sorting, with all the particles being roughly the same size?

Continental margins

Which of the following regions will primarily erupt silica-rich lavas?

Aphanitic

Which of the following textures indicates that a rock is volcanic in origin?

The granite would mechanically weather into small particles, which would travel down the slope of the mountain via mass wasting, be deposited, and undergo diagenesis when the sediments are buried under younger layers of rock.

Which of the processes listed below would transform an exposure of granite in the mountains into sedimentary rocks? Hint: Imagine you are adding a layer of cheese to lasagna that you are cooking. First you grate the cheese off of the block into a bowl. Next, you pour the bowl of cheese pieces onto the layer of sauce. Finally, you top the cheese with a new layer of pasta. How does this example compare to the process of transforming an exposure of granite into sedimentary rock?

Bivalves, corals, bacteria, and coccolithophores

Which of these aquatic organisms can form chemical sediments?

low grade, then intermediate grade, then high grade

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? Hint: Metamorphic grade describes how much the rock has metamorphosed, or changed from the original parent rock. A higher metamorphic grade indicates more change.

Deposition of carbonate sediments

Which process will remove C02 from the atmosphere and sequester it?

Since the minerals in the hornfels facies form under very low pressure, they would form as a result of contact metamorphism, as regional metamorphism would take place in be a high-pressure setting.

Which process would most likely form minerals belonging to the hornfels facies? Hint: In contrast with some other metamorphic environments that have consistent temperatures and pressures, the facies that result from regional metamorphism range from low pressures with low temperatures to high pressures with high temperatures.

-Quartzite -Marble -Hornfels

Which rocks does contact metamorphism create? PLEASE SELECT ALL THAT APPLY. Hint: Because contact metamorphism does not involve directional stress, it produces only nonfoliated rocks.

continental-continental convergent boundary

Which type of plate boundary is associated with regional metamorphism? Hint: Pressure is one of the two main agents responsible for regional metamorphism.

Because different minerals melt at different temperatures, minerals that melt at lower temperatures will melt from the rock first, creating a magma formed from the minerals that melted first. Felsic minerals melt at lower temperatures, so partial melting leads to a magma with a higher proportion of felsic minerals than the rock from which it was derived.

Why does partial melting result in a magma having a composition different from the rock from which it was derived? Hint: Keep in mind that for a solid to melt, the temperature must increase; for a liquid to solidify, the temperature must decrease.

Migmatites have both igneous and metamorphic qualities due to partial melting of the minerals they contain, as felsic minerals melt at much lower temperatures than mafic minerals.

Why is it difficult to place migmatites into one of the three basic rock groups? Hint: Migmatites form by the highest-grade metamorphism in an extremely hot environment.

Hydrothermal

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