Magma Basics

What are Igneous Rocks? "Igneous" is derived from the Latin word for “fire” - ignis. Thus, rocks that are “fire-formed”: molten rock (magma) cools to form a solid rock

What is magma?

Magma is molten rock, and contains:

Melt	Solids	Volatiles
Liquid, composed of mobile ions	Silicate minerals that have already crystallized from the melt	gases dissolved in the melt, including water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2)

How is magma made?

Heat

• Friction in subduction zones
• Crustal rocks heated during subduction
• Rising, hot mantle rocks

Pressure

• Increase confining pressure, increase temperature required to melt rock.
• Decrease pressure, decrease the temperature
• Rock can melt at a lower temperature

Volatiles

• Lowers the temperature required to melt rock
• Primarily water
• Where would you find this?

How does magma get to the surface?

Rocks at great depth	Rocks near the surface
Magma is less dense than the surrounding (host) rock Host rock warm, deform plastically Magma can easily push aside softened host rock	Host rock cold & brittle Magma ascends through fractures or stoping (blocks of wall rock break off and then sink into the magma)

<< HOME		next >>