The main difference between contact and regional metamorphism is that contact metamorphism occurs in a small region, whereas regional metamorphism occurs in a wide area.
In geology, metamorphism is the formation of metamorphic rocks. There are two major ways of forming a metamorphic rock: contact metamorphism and regional metamorphism. These two types of metamorphism mainly differ from each other according to the area in which metamorphism takes place. Moreover, contact metamorphism involves the contact of the rock with magma, while regional metamorphism involves collisions between continent-continent or oceanic and continental plates.
Key Areas Covered
1. What is Contact Metamorphism
– Definition, Features, Formation
2. What is Regional Metamorphism
– Definition, Features, Formation
3. What is the Difference Between Contact and Regional Metamorphism
– Comparison of Key Differences
Key Terms
Contact Metamorphism, Regional Metamorphism, Metamorphism
What is Contact Metamorphism
Contact metamorphism is the formation of a metamorphic rock due to the contact of magma. The contact of magma causes a sudden change in temperature of an existing rock. Generally, the term contact metamorphism refers to changes that take place when magma is injected into a solid rock. At the boundary where the rock comes into contact with the magma, there is a very high temperature. However, this temperature decreases with distance from this boundary.
Figure 1: Contact Metamorphism
Furthermore, the area where contact metamorphism occurs in an igneous rock is called the aureole. An aureole shows all possible degrees of metamorphism from the contact boundary to a distance away. Sometimes, we can also observe the formation of some important ore minerals at or near the contact region.
When a particular rock undergoes contact metamorphism by an igneous intrusion, the rock becomes coarsely crystalline and more indurated. This type of rocks are called hornstones while the term hornfel describes the product of this metamorphism.
What is Regional Metamorphism
Regional metamorphism is a type of metamorphism where the formation of a metamorphic rock occurs in a wide area. This type of metamorphism occurs with rocks that are buried deep down the Earth’s crust. Generally, this metamorphism technique is associated with plate boundaries and formation of mountains ranges. The areas affected by this change are very large.
Figure 2: Continental-continental Convergence
Rocks often form from regional metamorphism due to the continent-continent collisions. There can also be collisions between oceanic and continental plates. As a result of these collisions, young metamorphic belts, present-day continental margins and older metamorphic belts align parallel to each other. These alignments cause the formation of mountain belts such as Himalaya.
When there is a collision between oceanic and continental plates, the oceanic plate gets subducted beneath the continental plate. This is due to the high density of the oceanic plate compared to the density of the continental plate. This subduction can cause either a rise in temperature or the melting of hydrated peridotite (fluids released from the metamorphic reactions).
Difference Between Contact and Regional Metamorphism
Definition
Contact metamorphism is the formation of a metamorphic rock due to the contact of magma while regional metamorphism is a type of metamorphism where the formation of a metamorphic rock occurs in a wide area.
Area
Regional metamorphism occurs in a comparatively larger area when compared to contact metamorphism.
Process
Contact metamorphism involves contact of a rock with magma while regional metamorphism involves a collision between continental or oceanic plates.
Conclusion
Metamorphism is basically the process of forming a metamorphic rock. The main difference between contact and regional metamorphism is that contact metamorphism occurs in a small region, whereas regional metamorphism occurs in a wide area.
Reference:
1. “Contact Metamorphism.” Geology In, Available here.
2. “Regional Metamorphism.” Geology In, Available here.
3. Fyfe, William S., and Jane Selverstone. “Regional Metamorphism.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 15 Feb. 2019, Available here.
4. Earle, Steven. “7.4 Regional Metamorphism.” Physical Geology, BCcampus, 1 Sept. 2015, Available here.
Image Courtesy:
1. “Rock contact metamorphism eng big text” By Jasmin Ros – Own work, CC BY-SA 3.0) via Commons Wikimedia
2. “Continental-continental convergence en” By Nefronus (CC0) via Commons Wikimedia
Leave a Reply