Question 1

Plutonic rocks are emplaced at depth yet they can be seen at the Earth's surface due mainly to ________.
A)catastrophic violent upheavals that bring them to the surface
B)continual ongoing intrusion after the magma solidifies
C)erosion of overlying rocks due to uplift
D)widespread igneous inversion

Accepted Answer

Plutonic rocks are emplaced deep in the Earth's crust and are exposed at the surface due to erosion of the overlying rocks. As overlying rocks are eroded away due to uplift, the plutonic rocks get exposed at the surface. Catastrophic violent upheavals (option A) may cause the emplacement of volcanic rocks to the surface, but not plutonic rocks. Continual ongoing intrusion (option B) may lead to the growth of plutonic rocks, but not their exposure at the surface. Widespread igneous inversion (option D) is not a commonly accepted geological process. Hence, option C is the best choice.

Question 2

Silicate igneous rocks make up the ________.
A)bulk of volcanic mountains but not much else on Earth
B)bulk of the Earth's crust and mantle
C)densest rocks and are mainly found in the core
D)majority of shallow rocks covering the continents but everything deeper is sedimentary and metamorphic

Accepted Answer

Silicate igneous rocks, such as granite and basalt, make up the bulk of the Earth's crust and mantle. They are the most common type of rock found on Earth.

Question 3

The molten portion of magmas and lavas is made up of ________.
A)complex anion frameworks of oxygen with silicon and aluminum and cation modifiers made up of different amounts of calcium, sodium, iron, magnesium, and potassium
B)metamorphic fluids
C)silicate minerals that have already crystallized
D)solid high pressure forms of water, carbon dioxide, and sulfur dioxide

Accepted Answer

The molten portion of magmas and lavas is primarily made up of complex anion frameworks of oxygen with silicon and aluminum, and cation modifiers made up of different amounts of calcium, sodium, iron, magnesium, and potassium. This is due to the fact that magmas and lava are primarily composed of silicate minerals. Option B, C, and D are not correct as they do not accurately represent the composition of magma or lava.

Question 4

The earliest formed crystals (phenocrysts)in a magma tend to be ________.
A)crowded and irregular in shape
B)small and clouded with inclusions of everything that formed later on
C)those that can form only at the lowest temperatures
D)larger and well formed because they have space to grow and a ready supply of ions

Accepted Answer

The earliest formed crystals will have space to grow and a ready supply of ions, thus they will tend to be larger and well-formed.

Question 5

All of the following are factors that affect the generation of magma except for ________.
A)heat
B)pressure
C)crystal size
D)volatiles

Accepted Answer

Heat, pressure, and volatiles are all factors that can contribute to the generation of magma. Crystal size, however, is not a factor that affects magma generation.

Question 6

Three processes contribute to the formation of every igneous rock: ________.
A)assimilation, crystallization, and dyke injection
B)extrusion, intrusion, and consolidation
C)partial melting, buoyant rise, and crystallization
D)volcanism, plutonism, and magmatic differentiation

Accepted Answer

The three processes that contribute to the formation of every igneous rock are partial melting, buoyant rise, and crystallization. Assimilation, dyke injection, and magmatic differentiation are additional processes that can occur but are not necessary for the formation of igneous rocks. Extrusion, intrusion, and consolidation are terms used to describe the location and manner in which igneous rocks are formed, but they do not contribute to their formation. Finally, volcanism and plutonism are broad terms used to describe the types of igneous activity that lead to the formation of volcanic and plutonic rocks, respectively, but again, these terms do not describe the specific processes involved in their formation.

Question 7

Which of the following is the major dissolved volatile constituent in both magmas and volcanic gases?
A)carbon monoxide
B)methane
C)nitrous oxide
D)water

Accepted Answer

Water is the major dissolved volatile constituent in both magmas and volcanic gases. It is the most abundant volatile component and plays a crucial role in determining the explosiveness and style of volcanic eruptions. Other dissolved volatiles may include carbon dioxide, sulfur dioxide, and hydrogen sulfide, but they are typically present in much lower concentrations than water. Methane and nitrous oxide are not commonly found in magmas or volcanic gases.

Question 8

________ are dissolved in melts at depth but they have a tendency to evolve and vaporize at lower (atmospheric)pressure and drive volcanic processes.
A)Crystals of quartz and feldspar
B)Silica, sodium, and potassium
C)Volatiles
D)Volcanic lavas

Accepted Answer

Volatiles, such as water vapor, carbon dioxide, and sulfur dioxide, are dissolved in melts at depth but have a tendency to evolve and vaporize at lower pressures, driving volcanic processes. The other choices (A, B, and D) are not necessarily associated with the behavior of volatiles in magmas.

Question 9

The process of ________ is driven by ________ and transforms a magma into an igneous rock.
A)crystallization, cooling (heat loss)
B)intrusion, overlying rock weight
C)partial melting, pressure increase
D)volcanism, internal heating

Accepted Answer

Crystallization is the process of solidifying a magma into an igneous rock through the formation of crystals. This process is driven by cooling, which causes the magma to lose heat and solidify. As the magma cools, crystals form and grow, eventually turning the magma into a solid rock.

Question 10

The mechanism of magmatic differentiation involving the removal of denser, early formed high temperature mineral phases is ________.
A)assimilation
B)crystal settling
C)magma mixing
D)zone refining

Accepted Answer

Crystal settling happens when certain minerals that form at high temperatures and pressures sink to the bottom of a magma chamber due to their density. This process can lead to the removal of denser, early-formed high temperature mineral phases, which is a mechanism of magmatic differentiation. Assimilation involves the incorporation of foreign materials into a magma body, magma mixing involves the blending of two or more magmas to form a new mixture, and zone refining is a metallurgical process used to purify materials.

Question 11

Explosive volcanic eruptions occur ________.
A)when crystallization forces exceed the strength of the volcano
B)in response to deflation of the volcano
C)when violently escaping gases evolve suddenly to drop the magma density and propel molten magma from the chamber
D)whenever basaltic magma extrudes on the seafloor

Accepted Answer

Explosive volcanic eruptions occur when violently escaping gases (such as water vapor, carbon dioxide, and sulfur dioxide) evolve suddenly, dropping the magma density, and propelling the molten magma from the chamber. The gas pressure builds until it exceeds the strength of the rock or the confining pressure holding it down, leading to a sudden release of energy and an explosive eruption.

Question 12

The temperature within the Earth ________ with depth because rocks are poor conductors of heat and they contain small amounts of radioactive elements that generate heat.This gradual change in temperature with depth is called the ________.
A)increases, conductivity barrier
B)decreases, crustal thermocline
C)increases, geothermal gradient
D)increases, melting profile

Accepted Answer

The sentence mentions two factors that contribute to the gradual change in temperature with depth - poor conductivity of rocks and radioactive element-generated heat. This change is referred to as the geothermal gradient, making choice C the correct answer. Option A is incorrect because the sentence mentions that the temperature increases with depth, not that there is a conductivity barrier. Option B is incorrect because crustal thermocline is a term used to describe a layer within the ocean, not the Earth's interior. Option D is incorrect because while melting may occur at certain depths, the sentence is not referring to a melting profile specifically.

Question 13

Which statement best describes the crystallization of magmas?
A)Early formed crystals are big and irregular in shape, but gradually get smaller and have better developed faces with time as they react with the residual melt.
B)A felsic magma produces only one rock type equal to the melt composition by crystallizing quartz, feldspar, and ferromagnesian minerals in fixed proportions and compositions until all of the melt is used up.
C)During crystallization, which can occur over an interval of about 200° C, the composition of the residual melt continuously changes as particular ions are selectively removed and incorporated into certain minerals that crystallize early at high temperature.
D)Like the freezing of water, cooling magmas hit their crystallization temperature and stop cooling until all the melt has crystallized, whereupon cooling resumes.

Accepted Answer

During the crystallization of magmas, the composition of the residual melt continuously changes as certain ions are selectively removed and incorporated into minerals that crystallize early at high temperature. This process can occur over a range of temperatures, and the residual melt's composition may change continuously. The statement that early formed crystals gradually become smaller and have better-developed faces with time is accurate but not the best description of crystallization overall. Felsic magmas do indeed produce rock types based on specific compositions, but this statement is not comprehensive enough to capture the whole process of crystallization. Finally, the statement that cooling magmas stop at their crystallization temperature and resume cooling only after all the melt has crystallized oversimplifies the process.

Question 14

The behaviour and processes that govern the textures of magmatic rocks depend on the content of a magma's three distinct parts: ________.
A)andesite, basalt, and rhyolite
B)quartz, feldspar, and ferromagnesian minerals
C)solid, liquid, and gas
D)high pressure, medium pressure, and low pressure

Accepted Answer

The textures of magmatic rocks are influenced by the content of a magma's solid, liquid, and gas components, which affect its viscosity, cooling rate, and the formation of crystals.

Question 15

The last minerals to crystallize in Bowen's reaction series result in igneous rocks with a ________ composition.
A)felsic
B)intermediate
C)mafic
D)ultramafic

Accepted Answer

The last minerals to crystallize in Bowen's reaction series are the felsic minerals such as quartz and feldspar. Therefore, the resulting igneous rocks will have a felsic composition.

Question 16

Magmas rise to shallower depths and intrude the crust or extrude on the surface because ________.
A)of buoyancy, the magmas are hotter and less dense than the surrounding rocks where they form
B)of centrifugal and tidal forces as the Earth spins
C)the pressure at depth is so great that the magmas are forced upwards
D)earthquakes shake the crust and allow the magma to escape upwards

Accepted Answer

Magmas rise to shallower depths and intrude the crust or extrude on the surface due to buoyancy. The magmas are hotter and less dense than the surrounding rocks where they form, causing them to gradually rise towards the surface.

Question 17

As melts cool their viscosity increases (they lose their mobility and get stiffer)even before they start to crystallize because ________.
A)all of the sodium and potassium escape
B)their ions become more disordered
C)the silica tetrahedra in the melt start to link up and make larger and stronger units
D)they increase in volume

Accepted Answer

When melts cool, the silica tetrahedra in the melt start to link up and make larger and stronger units. This results in an increase in viscosity, even before crystallization begins.

Question 18

At about 100 km depth across most of the upper mantle, peridotite is about ________, which is very close to its melting temperature.
A)800°C to 1000°C
B)1000°C to 1200°C
C)1200°C to 1400°C
D)1400°C to 1800°C

Accepted Answer

The answer of At about 100 km depth across most...

Question 19

What is/are thought to be the main mechanism(s)for generating basaltic melts from hot peridotite near its melting point in the upper mantle?
A)conductive heating of basaltic ocean crust subducted into the mantle
B)frictional heating of basaltic ocean crust as it slides down subduction zones
C)intrusion of hotter solid mantle rocks from below
D)drop of confining pressure or introduction of water

Accepted Answer

The drop of confining pressure or introduction of water is thought to be the main mechanism for generating basaltic melts from hot peridotite near its melting point in the upper mantle. This can occur due to processes such as decompression melting or hydration melting, which result in the release of volatiles (e.g. water) and a reduction in the melting temperature of the mantle rocks. In contrast, options A, B, and C involve heating of pre-existing basaltic rocks rather than peridotite, and are not considered to be primary mechanisms for generating basaltic melts from peridotite.

Question 20

Consider Bowen's reaction series.Which mineral would you expect to see as a phenocryst in a porphyritic basalt?
A)olivine
B)quartz
C)orthoclase
D)sodium-rich plagioclase

Accepted Answer

Olivine is an early-forming mineral in Bowen's reaction series and is commonly found as phenocrysts in porphyritic basalt.

Quiz 3: Igneous Rocks

Plutonic rocks are emplaced at depth yet they can be seen at the Earth's surface due mainly to ________.

Silicate igneous rocks make up the ________.

The molten portion of magmas and lavas is made up of ________.

The earliest formed crystals (phenocrysts) in a magma tend to be ________.

All of the following are factors that affect the generation of magma except for ________.

Three processes contribute to the formation of every igneous rock: ________.

Which of the following is the major dissolved volatile constituent in both magmas and volcanic gases?

________ are dissolved in melts at depth but they have a tendency to evolve and vaporize at lower (atmospheric) pressure and drive volcanic processes.

The process of is driven by and transforms a magma into an igneous rock.

The mechanism of magmatic differentiation involving the removal of denser, early formed high temperature mineral phases is ________.

Explosive volcanic eruptions occur ________.

The temperature within the Earth with depth because rocks are poor conductors of heat and they contain small amounts of radioactive elements that generate heat.This gradual change in temperature with depth is called the .

Which statement best describes the crystallization of magmas?

The behaviour and processes that govern the textures of magmatic rocks depend on the content of a magma's three distinct parts: ________.

The last minerals to crystallize in Bowen's reaction series result in igneous rocks with a ________ composition.

Magmas rise to shallower depths and intrude the crust or extrude on the surface because ________.

As melts cool their viscosity increases (they lose their mobility and get stiffer) even before they start to crystallize because ________.

At about 100 km depth across most of the upper mantle, peridotite is about ________, which is very close to its melting temperature.

What is/are thought to be the main mechanism(s) for generating basaltic melts from hot peridotite near its melting point in the upper mantle?

Consider Bowen's reaction series.Which mineral would you expect to see as a phenocryst in a porphyritic basalt?