Contact vs Regional Metamorphism

Anne Dangerfield, Rebecca Gillaspy
  • Author
    Anne Dangerfield

    Anne has Bachelor’s and Master’s degrees in Geoscience from Brigham Young University. She worked as an oil and gas exploration geoscientist for eight years and is a specialist in rock structure, geochemistry, and plate tectonics. She also has four years of experience as a conservation scientist.

  • Instructor
    Rebecca Gillaspy

    Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Learn about contact metamorphism and regional metamorphism. Learn how each type of metamorphism occurs and see examples of contact metamorphic rocks and regional metamorphic rocks. Updated: 11/17/2021

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Metamorphic Rock

There are three high-level rock categories defined in geology: igneous rocks, sedimentary rocks, and metamorphic rocks. Each category is determined by how the rock type forms. This lesson will teach about metamorphic rocks. Metamorphic rock is any rock that has been changed or metamorphosed in a solid state in response to alterations in the surrounding conditions.

This lesson will examine the general principles of metamorphism and explain the two most common types of metamorphism, regional and contact metamorphism.

Process of metamorphism

The principles of thermodynamics state that all things try to reach a state of equilibrium corresponding to their surrounding conditions. If those conditions change, the object will re-equilibrate. Rocks are no exception to this rule. Metamorphic rocks form when a preexisting rock, called the protolith, experiences an environment different from the environment in which it formed; this is most commonly an increase or decrease in temperature or pressure. When the protolith rock is exposed to new pressure and temperature conditions, its mineral composition, mineral structure, and textures change to a stable form in the new environment. A key point in the definition of metamorphic rocks is that this transformation happens in the solid state, meaning the changing temperature or pressure does not melt the rock. Rocks that are formed from a melt, like magma and lava, are classified as igneous rocks. So, if the changing surroundings caused the protolith rock to melt and recrystallize, it would be classified as a metamorphic rock but as an igneous rock.

Limestone and marble are examples of a common protolith and resulting metamorphic rock. Limestone, the protolith, is changed into marble, the metamorphic rock, increasing pressure, and temperature. Both limestone and marble are made mostly of calcium carbonate, but they look entirely different. The higher temperature and press conditions force the calcium carbonate to change its crystal structure to a form stable under the new environment. Before the change, limestone usually is grey and featureless, not considered particularly pretty. On the other hand, marble tends to be bright white with subtle, wavy bands of gray. Its beautiful appearance makes it a popular choice for countertops and fireplace mantles.

Limestone

Limestone

Marble

Marble

Many earth processes change the surrounding environment of rocks. Each process creates unique temperature and pressure conditions and results in different types of metamorphic rock; if we understand a type of metamorphic rock, we can interpret how it was metamorphosed. Two main processes, or types, of metamorphism, are called contact and regional metamorphism.

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  • 0:07 Metamorphism
  • 0:37 Metamorphic Rocks
  • 1:15 Contact Metamorphism
  • 2:29 Regional Metamorphism
  • 3:48 Lesson Summary
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What is contact metamorphism?

The contact metamorphism definition is a specific metamorphism that happens when rocks meet a hot source that quickly raises their temperature. This rapid rise in temperature causes the rock directly surrounding the heat source to metamorphose through a series of chemical and mineral changes.

What is the major source of heat for contact metamorphism?

The primary heat source for contact metamorphism is an intrusion, or injection, of magma into existing, cooler rock layers; this most commonly happens at a volcano. During the formation of a volcano, hot, molten rock from the earth's interior intrudes upward and outward into the overlying earth's crust. These intrusions continue to happen until the magma reaches the earth's surface and erupts as lava to form a volcano. The crust underneath that volcano is full of rocks that the heat of repeated magma intrusions has metamorphosed.

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Frequently Asked Questions

What is an example of a regional metamorphic rock?

There are many different types of regional metamorphic rocks. The most common regional metamorphic rocks are slate, schist, and gneiss.

What is contact metamorphism?

Contact metamorphism is one of the main types of metamorphism. It is the transformation rocks undergo they come into contact with a very high heat source.

What is the process of contact metamorphism?

The process of contact metamorphism usually happens when a hot, magma body intrudes into the earth's crust. The magma heats the surrounding rock, causing it to metamorphose.

What happens during regional metamorphism?

During regional metamorphism, rock layers are compressed, folded, and buried. This process increases both the pressure and temperature environment surrounding the rocks and causes them to transform into a new rock that is stable in those conditions.

What is regional metamorphism in geology?

Regional metamorphism is one type of metamorphism in geology. It is the widespread transformation of rocks under high temperature and pressure conditions.

What is an example of contact metamorphism?

An example of contact metamorphism is limestone surrounding a magma chamber being turned into marble. This process happens because marble is a more stable form of rock in the magma intrusion's high heat area.

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