Geology: Magma and Its Properties

Study Notes

Molten rock located beneath the Earth's surface, specifically in the melted mantle rock and oceanic plate.

Asthenosphere: A hot, mobile layer of partially molten rock within the Earth's upper mantle.
The formation and movement of magma occurs in the asthenosphere.

Made up of silicate minerals, primarily feldspar and quartz.
Contains dissolved gases, including water vapor, carbon dioxide, hydrogen sulfide, and sometimes hydrochloric or sulfuric acid.

Geothermal gradient: The rate of increasing temperature with respect to increasing depth in the Earth's interior.
Partial melting: Rocks have different mineral compositions and therefore different melting points. When hot rocks start to melt deep in the Earth, some minerals melt while others stay solid.
Decompression melting: The upward movement of the Earth's mostly solid mantle (through convection) causes a decrease in pressure, resulting in a lower melting point and the formation of magma.
- Occurs at divergent boundaries where tectonic plates separate.
- Occurs at mantle plumes, columns of hot rock rising from the Earth's core to the crust.
Flux melting: Water or carbon dioxide added to rock causes the rock to melt at lower temperatures.
- Occurs around subduction zones where water from the subducting seafloor lowers the melting temperature of the mantle.

A measure of a fluid's resistance to flow.
Magma with high silica content has higher viscosity and flows less easily than magma with low silica content.
Dissolved gases can also influence viscosity.

Cooling and Solidification: As magma rises and cools, it crystallizes into igneous rocks.
Volcanic Eruptions: If magma reaches the surface, it erupts as lava.
Intrusive Igneous Rocks: Magma can solidify underground, forming intrusive igneous rocks like batholiths and dikes.