Question 1

On its slow journey through the crust,mafic magma evolves into intermediate magma by differentiation and assimilation of ______.

Accepted Answer

Mafic magma is low in silica and high in magnesium and iron, while intermediate magma has a higher silica content. This change is achieved through differentiation and assimilation of silicic rocks, such as granite, which are present in the crust.

Question 2

The coarse-grained equivalent of basalt is a(n)______.

Accepted Answer

Basalt is a fine-grained igneous rock, and its coarse-grained equivalent is gabbro.

Question 3

The melting point of a mineral generally _____ with increasing pressure (or depth).

Accepted Answer

The melting point of a mineral generally increases with increasing pressure (or depth). This is because at higher pressures, the mineral requires more energy to break the bonds between its atoms and molecules and reach its melting point.

Question 4

What type of melting takes place when a body of hot mantle rock moves upward and the pressure is reducted to the extent that the melting point drops to the temperature of the body?

Accepted Answer

This process is known as decompression melting. As the mantle rock rises, the pressure around it decreases, reducing the melting point until it reaches the temperature of the body. This process is common in areas associated with mid-ocean ridges or hot spots.

Question 5

What is the process through which magma differentiation takes place?

Accepted Answer

Magma differentiation takes place through crystal settling, where denser minerals sink to the bottom of the magma chamber and separate from the remaining magma. This process leads to the formation of different types of rocks, such as granite and basalt.

Question 6

Most of the basalt and gabbro on the ocean floor is created at mid oceanic ridges,which are also ____.

Accepted Answer

Mid oceanic ridges are locations where two tectonic plates are moving away from each other, which is characteristic of divergent plate boundaries. This is where new oceanic crust is formed through volcanic activity, resulting in the formation of basalt and gabbro.

Question 7

Crystal settling accounts for important deposits of ______.

Accepted Answer

Crystal settling in magmatic differentiation processes can lead to the concentration of chromium and platinum, as these heavy elements can settle to the bottom of a magma chamber.

Question 8

Hawaii and __________ eruptions are related to intraplate igneous activity.

Accepted Answer

Hawaii and Yellowstone both have intraplate igneous activity, while Japan, the Cascade range, Honduras, and California are related to subduction zones.

Question 9

________ lava is largely restricted to narrow zones along convergent plate boundaries.

Accepted Answer

Andesite lava is primarily found near convergent plate boundaries where oceanic crust is subducted beneath continental crust. This type of lava is typically gray or brown in color and is intermediate in viscosity and silica content between basaltic and rhyolitic lavas. Granite, rhyolite, ultramafic, and carbonate lavas are not primarily associated with convergent plate boundaries.

Question 10

The huge volume of mafic magma that erupted to form the Columbia plateau basalts of Washington and Oregon are attributed to ___.

Accepted Answer

The huge volume of mafic magma that erupted to form the Columbia plateau basalts of Washington and Oregon are attributed to a hot mantle plume. These plumes are thought to be columns of hot material that rise from deep within the Earth's mantle, and can cause large-scale volcanic activity when they reach the surface.

Question 11

Viscosity is a property of a fluid that relates to how easily the fluid flows.A material that is viscous __.

Accepted Answer

A material that is viscous flows less easily.

Question 12

How is a sill different from a dike?

Accepted Answer

The answer of How is a sill different from a...

Question 13

Imagine two magmas that are identical in all respects (for example,same chemistry,pressure,volume)except that one magma is hotter than the other.Which magma will have the higher viscosity?

Accepted Answer

The cooler magma will be more viscous because viscosity decreases with increasing temperature. In other words, as magma cools, it becomes thicker and flows less easily.

Question 14

The crust beneath the world's oceans is mafic ________.

Accepted Answer

Mafic crust is composed of basalt and gabbro, which are both igneous rocks rich in minerals like magnesium and iron. Iron and asthenosphere are incorrect choices because iron is not a type of rock, and the asthenosphere is a layer of the Earth's mantle, not the crust. Granite and rhyolite are not mafic rocks and are commonly found in continental crust rather than oceanic crust.

Question 15

Geologists regard basaltic magma (Hawaiian lava,for example)as the result of the partial melting of ultramafic rock in the ____.

Accepted Answer

Basaltic magma is formed from the partial melting of ultramafic rock in the mantle. The oceanic crust is primarily composed of basalt, which is formed from basaltic magma that has solidified. The continental crust is mainly composed of granite, which is a product of the partial melting of the lower crust. The outer core is molten iron and nickel, while the inner core is solid iron and nickel.

Question 16

The first plagioclase crystals to form as a hot melt cools are high in ______.

Accepted Answer

The first plagioclase crystals to form as a hot melt cools are high in calcium.

Question 17

What is the sequence of crystallization along the discontinuous branch of Bowen's reaction series?

Accepted Answer

The discontinuous branch of Bowen's reaction series pertains to the crystallization of mafic minerals from a magma. The sequence of crystallization along this branch starts with olivine, followed by pyroxene, amphibole, and finally biotite.

Question 18

To explain the great volumes of granite plutonic rocks,most geologists think that partial melting of the _______ must take place.

Accepted Answer

The lower continental crust is composed of granitic rocks which have similar composition to granite plutonic rocks. Geologists think that partial melting of the lower continental crust must take place to explain the large volumes of granite plutonic rocks.

Question 19

Granite and ______ are composed predominantly of feldspar and quartz.

Accepted Answer

The answer of Granite and ______ are composed predominantly of...

Question 20

Mafic magma generated in the _______ rises to the base of the crust.

Accepted Answer

The answer of Mafic magma generated in the _______ rises...

Quiz 11: Igneous Rocks, Intrusive Activity, and the Origin of Igneous Rocks