Question

How does contact metamorphism differ from region metamorphism?

Answer 1

Hint: Metamorphism is the process of mineralogical structural adjustment of pre-existing rocks due to physical and chemical conditions. The word metamorphism has entomological roots in ancient Greek and means “after form”. Metamorphism occurs at temperatures higher than 200°C and pressures higher than 300 MPa which mostly take place during continental collisions or subduction. The increase in temperature and pressure on the rocks is called prograde metamorphism or the grade of metamorphism. A lower grade of metamorphism takes place between the temperatures of 200-320°C and higher grade of metamorphism takes place above 320°C.

Complete answer: Apart from grades, metamorphism can also be subdivided into various types based on the process itself. Here are the basic differences between two such categories.

Contact Metamorphism	Regional Metamorphism
-Contact metamorphism takes place next to igneous intrusions and is caused by high temperatures associated with the igneous intrusion.	-Regional metamorphism results from tectonic forces that produce compressional stresses in the rocks.
-It is restricted to the zone surrounding the intrusion called the contact aureole and the grade of it decreases as it extends further before diminishing completely.	-It takes place over larger areas and does not show any relationship to igneous bodies.
-It is called high temperature, low-pressure metamorphism because the temperature is higher affected by the magma but the pressure in shallow levels of the crust is lower.	-Unlike contact metamorphism, this process occurs in the cores of fold mountains or eroded mountain ranges.
-It produces fine-grained rock that shows no foliation like hornfels.	-It forms strongly foliated rocks like slates, schists, and gneisses.

Note: Based on various processes of metamorphism, two types of metamorphic rocks are formed— foliated and nonfoliated. Examples of foliated rocks are slate, phyllite, schist, gneiss, etc and examples of non-foliated rocks are marble, quartzite, hornfels, anthracite coal, etc.