GeologyRocks

The way I undersand it is that metamorphism is the alteration of rocks by heat and/or pressure, and metasomatism is the alteration of rocks by hydrothermal minerals.

John

“Civilisation exists by geological consent, subject to change without notice.” -  Will Durant

That's the way I understand it too, although quite often metamorphic processes can involve both.

Yes. Almost certainly there will be some extremely hot fluids around during metamorphism.

John

“Civilisation exists by geological consent, subject to change without notice.” -  Will Durant

Thanks for the explanation. It means the metamorphic facies is also related in metamorphism? If im right?

Yes you're right.  Metasomatism is a form of metamorphism as it also involves the alteration of rocks, it's just a specific type of metamorphism involving the movement of fluids.  An example here in Cornwall is the movement of fluids in a batholith due to the circulation of hot fluids following contact metamorphism of the surrounding rocks by heat.  In this case it is metamorphism followed by metasomatism.