Igneous rocks

Igneous rocks

Rocks formed from crystals of one or more minerals bound together in a mixture.

Two main types of igneous rocks

Extrusive and intrusive igneous rocks.

Extrusive igneous rocks

Magma erupts on Earth's surface and cools rapidly, resulting in fine-grained texture.

Examples of extrusive igneous rocks.

Basalt and pumice.

Intrusive igneous rocks

Form deep underground when magma cools and solidifies slowly, resulting in coarse-grained texture.

Examples of intrusive igneous rocks.

Granite and diorite.

Temperature range of molten rock

650-1200 degrees Celsius.

Geotherm

A representation of the temperature structure of Earth's interior.

Decompression melting

Melting that occurs due to a sudden geological decrease in pressure, allowing molecules more room to move.

Volatiles

Substances like water and carbon dioxide that can change the chemical composition of the system and decrease melting temperature.

Solidus temperature

The temperature at which a rock begins to melt.

Liquidus temperature

The temperature at which a rock is fully molten.

Fractional crystallization

The process of removing specific elements from a melt, changing the relative abundances of elements in the system.

Bowen's reaction series

A sequence that describes the order in which minerals crystallize from a cooling magma.

What factors affect the viscosity of magma?

Temperature, crystal content, and gas content.

What type of eruption is associated with low-viscosity magma?

Effusive eruptions, which allow gas to escape easily.

Vesicles

Gas bubbles that are trapped within the rock.

Mafic vs felsic magma

Mafic magma has lower silica content and is less viscous, while felsic magma has higher silica content and is more viscous.

What type of eruptions are associated with felsic magma?

Explosive eruptions due to high viscosity and gas content.

Lahar

A water-rich slurry of volcanic debris that can flow down slopes.

Mid-ocean ridges

Constructive margins where melting occurs via decompression.

How does subduction contribute to igneous rock formation?

It introduces volatiles into the mantle, leading to melting and the formation of felsic melts.

What is the source of melt in continent-continent collisions?

The crust, which often leads to the formation of granite plutons.

Hot spot

A location where a plume of hot mantle material rises, leading to volcanic activity.

Magmatic intrustions

magma forces its way into existing rock layers through existing planes of weakness and solidifies

Sill

flat, sheet-like intrusion of igneous rock that runs parallel to existing rock layers

Dike

sheet-like rock formation that cuts across existing rock layers

Pluton

solidified blob-shaped large magma chamber in the crust

Batholith

huge mass of intrusive rock made of numerous plutons

Composition of igneous rocks

Si, H, K, Na, Fe, Ca, O, Mg, Al