Mafic

Definition

Mafic refers to igneous rocks and magmas that are rich in magnesium and iron, typically resulting in darker colors and denser materials. This term is significant because it helps classify rocks based on their mineral composition, which directly relates to their formation processes in Earth's internal structure, the characteristics of magma, and the textures found in various igneous rocks.

5 Must Know Facts For Your Next Test

1. Mafic magmas have lower viscosity compared to felsic magmas, allowing them to flow more easily during volcanic eruptions.
2. The presence of iron and magnesium in mafic rocks contributes to their dark coloration, which contrasts with the lighter hues of felsic rocks.
3. Mafic rocks like basalt and gabbro are often associated with oceanic crust formation, as they are the predominant rock types found in mid-ocean ridges.
4. The mineral composition of mafic rocks typically includes olivine, pyroxene, and amphibole, distinguishing them from felsic counterparts.
5. Mafic magma can form from partial melting of the upper mantle, which has a higher concentration of iron and magnesium compared to continental crust materials.

Review Questions

• How does the mineral composition of mafic rocks influence their physical properties compared to felsic rocks?
  • Mafic rocks contain higher amounts of magnesium and iron, which contribute to their density and darker color. In contrast, felsic rocks are richer in silica and lighter elements, making them less dense and typically lighter in color. This difference in mineral composition affects not only their appearance but also their behavior during volcanic activity; mafic magmas are more fluid and have lower viscosity compared to the thicker, more viscous felsic magmas.
• Discuss the role of mafic magmas in the formation of oceanic crust and how this relates to plate tectonics.
  • Mafic magmas play a crucial role in the formation of oceanic crust, primarily at mid-ocean ridges where tectonic plates diverge. As the plates separate, magma from the mantle rises to fill the gap, creating new oceanic crust predominantly made up of basalt. This process is integral to plate tectonics as it contributes to seafloor spreading and influences global geological activity, including volcanic eruptions associated with divergent boundaries.
• Evaluate the implications of mafic rock formation on Earth's internal processes and how it affects surface geology.
  • The formation of mafic rocks has significant implications for understanding Earth's internal processes. Their origin from partial melting of the upper mantle reveals insights into the chemical composition and temperature conditions of this layer. Moreover, as mafic rocks make up much of the oceanic crust, they affect surface geology by influencing ocean basin topography and contributing to volcanic activity. The dynamics between mafic magma generation and tectonic plate movements help explain various geological phenomena including earthquakes and the creation of new landforms.

Related terms

Felsic: Felsic describes igneous rocks and magmas that are rich in silica and lighter elements, resulting in lighter colors and lower densities compared to mafic rocks.

Basalt:

Basalt is a common mafic volcanic rock, known for its fine-grained texture and dark color, formed from rapid cooling of lava at or near the Earth's surface.

Gabbro:

Gabbro is a coarse-grained mafic intrusive rock formed from the slow cooling of magma beneath the Earth's surface, containing minerals such as pyroxene and plagioclase.