Geos Chapter 5

Select the correct statements about a magma's cooling history by using the graph.

-At point 2, magma is a liquid - At point 4, magma is solid - At point 1, magma is a liquid.

Select four factors that can directly determine how far a magma can rise toward Earth's surface.

- gas pressure - tectonic stresses - magma pressure - density of magma

What occurs when a rock melts due to decompression?

There is a decrease in pressure.

How do the rocks that form from molten rock reach the surface?

They erupt in a volcano. They solidify underground and are later uplifted and exposed by erosion.

True or false: A hot, solid rock can melt if water is introduced into the system without a change in temperature or pressure.

True

True or false: Magma can be produced during continental collisions due to the release of water by minerals that are metamorphosed.

True (Both heat and water can create magma but it rarely makes it to the surface.)

True or false: The complete melting of a source area to form igneous rocks is rare.

True (Most magmas result from partial melting.)

Rocks at mid-ocean ridges are formed from ______ magmas.

basaltic

Felsic minerals melt ______ mafic minerals.

before (As a rock undergoes heating, the felsic minerals will melt before the mafic minerals because they melt at lower temperatures.)

Most subduction-derived magma never reaches the surface. However, if this type of magma reaches the surface of a continent, ______ are formed.

belts of volcanoes

Crystals in coarse-grained igneous rocks normally _____ be seen with the unaided eye.

can

Igneous rocks contain different minerals so their ________ composition varies.

chemical

A hand lens could be used to examine a(n) _______ -grained igneous rock, while a(n) ______ would be needed to examine the crystals in a fine-grained igneous rock. (Use just one word for each answer.)

coarse or medium microscope

The grain size of ______ igneous rocks is larger than 1 millimeter. More commonly, this grain size is described as being large enough to see with the unaided eye.

coarse-grained

Source rock types and temperatures as well as other factors can affect the of magma. After magma forms, this property can be changed by crystallization, assimilation, or mixing.

composition or viscosity

Conduction is the transfer of heat by direct *contact*. *radiant* heat transfer is the movement outward of heat from a heated surface. Convection is heat transfer by moving *liquids* and solids.

contact Radiant liquids or fluids

There are diverse igneous rocks associated with continental rifts because melting occurs in both the _____ and the _____

crust or lithosphere mantle or asthenosphere

Igneous rocks are broadly divided into two categories: those that have crystals, that can be seen with the unaided eye and those that require some type of magnification.

crystals or minerals

Melting of the asthenosphere occurs at mid-ocean ridges through the process of

decompression

When solid rock retains its heat as it moves up from depth, melting occurs due to

decompression

When two plates are moving away from each other, they are said to be ______.

diverging

An ______ igneous rock is one that solidifies on Earth's surface.

extrusive

The temperature increase with depth is called the geothermal ______.

gradient

Mafic magma that encounters continental crust provides the ______ needed to melt the continental crust and produces felsic magma.

heat

Radioactive decay, impacts of meteors, initial collisions, and compression of materials by gravity are some of the sources of ______ for early Earth.

heat

Mafic magma can influence the formation of felsic magma by ______.

heating the continental crust, which becomes liquid; the mafic magma loses heat in the process and becomes solid

Rock that has formed from cooling magma or lava is ______ rock.

igneous

Continental rifts have a diverse suite of igneous rocks associated with them because melting occurs ______.

in the mantle and in the crust

Minerals crystallize ______.

in the opposite order that they melt

In a solid, atoms and their bonds are always vibrating. As temperature increases, the vibrations _____, leading to melting. Pressure has the opposite effect, compressing the solid, making it more resistant to melting.

increase

Temperature and pressure within Earth ________ as depth increases.

increase

The geothermal gradient is the ______.

increase of Earth's temperature with increase in depth

An igneous rock that solidifies below the surface is a(n) ______ rock.

intrusive

Most subduction-derived magma never reaches the surface. However if this type of magma reaches oceanic crust, then ______ are formed.

island arcs

Molten rock on Earth's surface is

lava

Adding water can significantly ______ the temperature at which a rock can melt.

lower

Felsic minerals melt before _______ minerals

mafic

Partial melting of the mantle produces _____ (composition) magma.

mafic

Conduction, convection, and radiation of heat are the ways that thermal energy can escape from ________ as it cools.

magma

When an oceanic plate subducts into the mantle at a convergent boundary, ______ is formed.

magma

Hot spots are places where _____ activity is not explained by being located on a mid-ocean ridge or subduction zone.

magmatic, igneous, volcanic, or magma

Most hot spots are considered to be the result of rising plumes of hot material from the _______.

mantle

Minerals crystallize in the opposite order that they

melt

Lava is molten rock that cools ______.

on the surface

Igneous rocks vary in their chemical composition and subsequently in their ______.

mineral content

Tuff and volcanic breccia are both composed of a variety of igneous fragments. Their classification as either felsic, intermediate, or mafic therefore depends on the particular ______ of each individual rock.

mineral content

These igneous rocks can be classified using their color which reflects the types of _____ within the rocks, and using their texture.

minerals

Magma is generated along a subduction zone as ______.

minerals in the subducted plate release water, which lowers the melting temperature of the mantle material above

Place the following minerals in order of their crystallization from a magma as it cools from high to low temperatures. The mineral that crystallizes at the highest temperature should be at the top.

olivine Pyroxene Biotite Muscovite Quartz

A magma that does not flow easily is described as ______.

viscous

The creation of magma in a subduction requires the addition of _______, the source of which comes from minerals in the down-going ______ crust.

water oceanic or ocean

Which of the following is not a factor that affects the viscosity of magma?

Climate

To study an igneous rock with a phaneritic texture, a geologist would likely use ______.

a hand lens

1. Felsic 2. Mafic/ultramafic 3. Intermediate

1. Abundant quartz and feldspar; light colored 2. Abundant magnesium and iron; dark colored 3. Mineral content in between; color moderate

Match the name of the igneous rock on the left with its compositional term on the right. Instructions 1. Granite 2. Diorite 3. Basalt 4. Peridotite

1. Felsic 2. Intermediate 3. Mafic 4. Ultramafic

1. Volcanic Glass - 2. Fine-grained Igneous rocks - 3. Course-grained igneous rocks - 4. Vesicles -

1. Forms when magma erupts on the surface and cools quickly with no crystal formation 2. Forms when magma only has enough time to grow small crystals 3. Forms when magma has a slow cooling rate, which results in large crystals 4. Forms when gases dissolved in magma accumulate as bubbles

1. Aphanitic 2. Phaneritic 3. Porphyritic

1. Igneous rocks with crystals only visible with the aid of a microscope 2. Igneous rocks with crystals that are visible to the unaided eye 3. Igneous rocks with large crystals in a fine-grained matrix

Match the igneous rock with its appropriate classification. 1. Obsidian 2. Scoria 3. Pumice

1. Mostly felsic 2. Mostly mafic 3. Felsic to intermediate

Match the igneous rock texture with the location where it is likely formed. 1. Pegmatitic 2. Porphyritic 3. Vesicular

1. Pegmatitic A: deep within Earth in the presence of water 2. Porphyritic A and B: first deep within Earth and then later near the surface 3. Vesicular B: near Earth's surface, as gas bubbles through the lava

Match the process involved with forming new oceanic crust at divergent boundaries with the correct position on the image. Instructions

As plates separate, solid mantle rock rises and becomes fluid through decompression melting A Magma rises upward through magma-filled fractures that form as plates diverge from each other. B Older oceanic crust moves away as new oceanic crust is produced along the area of the ridge. C

Match the terms regarding heat transfer between objects to their correct definitions. Instructions

Conduction: Heat transfer by direct contact Radiant heat transfer: Heat that moves outward from a source (between objects that are not touching) Convection: Heat transfer by moving material

Rank the following types of igneous rocks according to silica composition, with the highest percent of silica at the top.

Felsic Intermediate Mafic Ultramafic

Select all the statements that are correct for cooling magma.

Groundwater can receive heat from magma by conduction. When magma reaches the surface of Earth, thermal energy is transferred to the atmosphere and land surfaces by conduction and radiation. Magma can lose heat when it releases gases either underground or above ground. At depth magma loses thermal energy to the surrounding rocks by conduction.

Use the graph, which relates temperature and pressure, to answer this question. What happens to the rock that moves from position C to position B?

It melts due to a decrease in pressure.

Match the type of igneous rock on the left with its silica composition on the right. Instructions

Mafic: Contains about 44% to 50% silica Felsic: Contains 70% to 77% silica Intermediate: Contains about 60% silica Ultramafic: Contains 43% or less silica

Select the three ways in which magma can travel through Earth's crust.

Magma can travel through existing fractures in rock, forming fissures and dikes. Magma can travel in regions where tectonic forces have newly fractured solid rocks. Magma can travel upward as rocks above magma chambers collapse.

During the collision of two continents, one continent may slide beneath the other, getting hotter due to increased pressure. Select two reasons why the small amount of magma produced may never reach the surface to form volcanoes.

Magma may solidify as it rises. The crust is too thick for magma to push through.

Match a factor on the left that determines how far magma can rise toward Earth's surface with its definition.

Magma pressure - Pressure of the overlying rock is directed toward the magma from all sides; Density - Magma is less dense than surrounding solid rock and thus rises; Gas pressure - Carbon dioxide and sulfur oxide bubbles form in magma, decreasing density of the magma; Stress - Opening of fractures is induced by tectonic forces.

Match the igneous rock example on the left with its description on the right.

Obsidian: Shiny volcanic glass Pumice: Contains vesicles and can float on water Scoria: Contains many vesicles; usually dark to reddish in color Tuff: Ash, pumice, crystals, and rock fragments that may be welded Volcanic breccia: Fragmented igneous rock Pegmatite: Contains very large crystals

What is the source of water necessary to induce the production of magma in a subduction zone?

Ocean water incorporated into crust at divergent plate boundaries

Which of the following factors influence the composition of a magma?

Partial crystallization The completeness of the melting of the parent rock(s) The type of source area Assimilation and magma mixing

From the list below, select the terms that are associated with igneous rocks that have crystals observable by the unaided eye.

Pegmatite Phaneritic Porphyritic

Which of the following minerals would crystallize from a magma at the lowest and highest temperatures, respectively?

Quartz/olivine

Which of the following produced significant amounts of heat during the early formation of Earth, which started approximately 4.5 billion years ago?

Sinking of the molten iron and nickel into Earth's interior Collision and compression of materials by gravity Impacts of meteors and asteroids

In the formation of an igneous rocks, melting needs to occur first, which happens in the _______ area.

Source

Select the factors that directly control the viscosity of magma.

Temperature Composition Crystal content

The melting of rock to form magma is influenced mainly by which of the following three factors?

Temperature Water content Pressure

Use the graph, which relates temperature and pressure, to answer this question. What is required if a rock in position B moves to position A on the graph?

Temperature would have to decrease.

Select the correct statements about how partial melting of the continental crust affects the crust.

The continental crust is divided into the upper felsic and the lower mafic or intermediate. The lower crust is more mafic than the upper crust. Felsic magma carries felsic materials toward the upper crust as it rises.

Select the characteristics listed below that could be used to classify the igneous rocks in the image.

The mineral content The aphanitic or phaneritic nature of the rocks

Choose all the following that correctly describe the processes involved in the formation of igneous rocks.

Volcanic igneous rocks are formed when magma erupts at the surface. Magma accumulates in large chambers and cools slowly to form intrusive igneous rocks.

An ophiolite is identical to ______.

a newly formed segment of oceanic crust, except it contains an additional layer of sediment

An ophiolite is ______.

a sliced-off piece of oceanic crust that has been thrust onto the edge of a continent or island

Rocks of the continental crust contain different minerals and each mineral has its own melting point. If the minerals with the lowest melting temperatures are the only ones melted, this is referred to as ______ melting.

partial

Most rocks contain more than one mineral, and each mineral has its own melting point. If only the lower temperature minerals melt, this is referred to as _____ melting.

partial melting

Put the following processes in the correct order of how an igneous rock forms. Place the first step at the top (even though it occurs deepest within Earth.)

partial melting of rock in the deeper parts of the crust or mantle forms magma magma rises ad some accumulate in pockets accumulated magma could solidify in chambers or continue upward magma may reach the surface and erupt as lava

The process that produces mafic magma is ______.

partial melting of the mantle

When igneous rocks are formed, the source area usually ______.

partially melts

Igneous rocks have various textures: crystals that can be seen without an aid are called ______; very small crystals are called ______; and a rock with two distinct crystal sizes is ______.

phaneritic; aphanitic; porphyritic

If the pressure and bond strength are sufficient to overcome vibrations due to an increase in temperature, a rock or mineral will ______.

remain solid

Basaltic magma forms the rock at mid-ocean

ridges

The primary chemical component of igneous rocks is _____, which ranges between 44% and 77%.

silica

The most common chemical compound in igneous rocks, varying between 44% and 77%, is

silica, SiO2, or silicon dioxide

The higher a magma's viscosity is, the ______.

slower it will flow

The place in the crust or mantle where igneous rocks begin to form is called the ______ area.

source

Pressure from magma and ______ forces produce fractures through which magma can move.

tectonic

A continental rift occurs when ______.

tectonic forces split a continent apart

The three primary factors that control rock melting are ______, _______, and the presence of water.

temperature pressure

Classifying an igneous rock as a breccia is based on its ______, whereas the classification of scoria and pumice is more closely related to their ______.

texture; composition

As depth increases into Earth, ______.

there is an increase in temperature and pressure