Chapter 3: Problem 6

What must happen within a magma chamber for fractional crystallization to take place?

Short Answer

Expert verified

For fractional crystallization to occur within a magma chamber, the magma must cool, allowing minerals with different melting points to crystallize selectively. As these minerals crystallize, they separate from the remaining magma due to density differences, with denser crystals sinking and less dense ones rising. This process alters the magma's composition and forms distinct rock layers. The remaining magma continues to cool and crystallize, yielding a diversity of rock compositions in the solidified magma chamber.

Step by step solution

Introduction to Magma Chamber

A magma chamber is a region beneath the Earth's surface where molten rock material (magma) is accumulated. Magma chambers form due to various geological processes such as tectonic plate movements, volcanic activity, and mantle plume activity. The composition of magma within a chamber varies, and it is comprised of minerals, dissolved gases, and other constituents.

Understanding Fractional Crystallization Process

Fractional crystallization is a process in which magma cools and crystallizes selectively, resulting in the formation of rocks with different mineral compositions. During the fractional crystallization process, the minerals with a higher melting point crystallize first, followed by those with progressively lower melting points. These newly formed crystals either sink to the bottom or float to the top of the magma chamber due to their varied densities, thus changing the composition of the remaining magma.

Phase One: Cooling of Magma

For fractional crystallization to take place, the first requirement is the cooling of the magma within the chamber. As the temperature decreases, minerals with higher melting points will start to crystallize. The speed at which the magma cools affects the size of the crystals formed. Slow cooling allows for the growth of larger crystals, whereas faster cooling leads to the formation of smaller crystals.

Phase Two: Variation in Mineral Composition

The second requirement for fractional crystallization is a wide range of minerals with different melting points present in the magma chamber. These minerals will begin to crystallize selectively at distinct temperatures. As each distinct mineral crystallizes, it separates from the magma, gradually altering the magma's mineral composition.

Phase Three: Crystal Separation

Once the crystals have formed in the cooling magma, they must separate from the remaining liquid. This can occur due to differences in their densities and is aided by gravitational settling, where denser crystals sink and less dense crystals rise. This separation results in different rock layers, with each layer exhibiting a distinct mineral composition.

Phase Four: Continuous Cooling and Crystallization

Lastly, the remaining magma continues to cool and crystallize, resulting in the formation of new minerals with different compositions. Over time, this process produces a diversity of rock compositions in the solidified magma chamber due to the progressive change in its mineral content. In conclusion, for fractional crystallization to take place within a magma chamber, the following steps must occur: cooling of the magma, variation in mineral composition, separation of formed crystals, and continuous cooling and crystallization of the remaining magma.

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What must happen within a magma chamber for fractional crystallization to take place?

Short Answer

Step by step solution

Introduction to Magma Chamber

Understanding Fractional Crystallization Process

Phase One: Cooling of Magma

Phase Two: Variation in Mineral Composition

Phase Three: Crystal Separation

Phase Four: Continuous Cooling and Crystallization

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