Question 1

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

Accepted Answer

Mafic magma is typically generated in the asthenosphere, which is part of the upper mantle, and then rises to the base of the crust.

Question 2

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

Accepted Answer

The coarse-grained equivalent of basalt is gabbro, as basalt and gabbro are extrusive and intrusive equivalents of each other respectively. Andesite, diorite, and rhyolite are all different types of volcanic rocks that have different compositions and textures compared to basalt. Granite is a type of intrusive rock, but it has a different composition and texture compared to gabbro.

Question 3

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

Accepted Answer

Plagioclase crystals are made up of calcium, sodium, and aluminum silicates. As the hot melt cools down, the first plagioclase crystals to form are rich in calcium.

Question 4

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, which is made up of granitic rocks, is the most likely source for the partial melting that produces granite plutonic rocks. The core, lower mantle, oceanic crust, and asthenosphere are not typically associated with the formation of granite plutonic rocks.

Question 5

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

Accepted Answer

Generally, the melting point of a mineral increases with increasing pressure (or depth). This is because higher pressures increase the average distance between atoms or ions, making it more difficult for them to break apart and melt. However, there are some exceptions to this general trend and the melting point can also be influenced by other factors like the composition and structure of the mineral.

Question 6

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

Accepted Answer

The eruption of the Columbia plateau basalts is attributed to a hot mantle plume, which is a thermal anomaly in the Earth's mantle that can melt and produce large volumes of magma.

Question 7

Granite and ______ are composed predominantly of feldspar and quartz.

Accepted Answer

Rhyolite, like granite, is composed predominantly of feldspar and quartz, but it is the extrusive volcanic equivalent of granite.

Question 8

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 divergent plate boundaries where two plates move away from each other, leading to the creation of new oceanic crust through volcanic activity. Basalt and gabbro are igneous rocks commonly found in the ocean floor, and they are produced by the solidification of molten material (magma) that rises up from the mantle and cools down at the mid-oceanic ridges. Therefore, the correct choice is A.

Question 9

Hawaii and __________ eruptions are related to intraplate igneous activity.

Accepted Answer

The intraplate igneous activity that leads to volcanic eruptions is associated with hot spots. Hawaii and Yellowstone are two well-known examples of hot spots, while the other options (Japan, Cascade, Honduras, and California) are not necessarily associated with this type of volcanic activity.

Question 10

How is a sill different from a dike?

Accepted Answer

Sills are parallel to the layering in the country rock, whereas dikes cut across the layering.

Question 11

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

Accepted Answer

Andesite lava is typically found at convergent plate boundaries where oceanic plates are being subducted beneath continental plates. This type of lava often forms stratovolcanoes, such as those found in the Pacific Ring of Fire. Granite, rhyolite, and ultramafic lava are not typically associated with convergent plate boundaries. Carbonate lava does not exist.

Question 12

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

Accepted Answer

Viscous materials flow less easily due to internal friction between the molecules.

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

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 type of melting is known as decompression melting, which occurs when hot mantle rock moves upward and the pressure is reduced to the point where the melting point drops to the temperature of the body. As the pressure decreases, the rock begins to melt and forms magma. This process is commonly associated with the formation of mid-ocean ridges and volcanic hotspots.

Question 15

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

Accepted Answer

Mafic magma contains a lower concentration of silica. Through differentiation and assimilation, the magma can acquire more silica from the surrounding rocks, ultimately leading to the formation of intermediate magma with a higher concentration of silica. Silicic rocks would be the most likely source of this added silica.

Question 16

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

Accepted Answer

The mafic crust beneath the world's oceans is primarily composed of basalt and gabbro.

Question 17

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 18

What is the process through which magma differentiation takes place?

Accepted Answer

Magma differentiation occurs through crystal settling, which is the process where denser minerals sink to the bottom of the magma chamber while lighter minerals float to the top. This process ultimately leads to the formation of different layers of rocks with varying mineral compositions.

Question 19

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 describes the sequence of crystallization of mafic minerals that occur at high temperatures and pressures. The sequence begins with olivine and pyroxene, and then progresses to amphibole and biotite.

Question 20

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

Accepted Answer

Geologists believe that basaltic magma is the result of partial melting of ultramafic rock in the mantle, specifically in the upper part of the mantle known as the asthenosphere.

Quiz 3: Igneous Rocks, Intrusive Activity, and the Origin of Igneous Rocks