Ultramafic

Definition

Ultramafic refers to igneous rocks that contain a very high percentage of magnesium and iron, typically with low silica content. These rocks are primarily composed of minerals like olivine and pyroxene, and their composition significantly influences the characteristics of magma and the types of igneous rocks that form during volcanic and tectonic activities.

5 Must Know Facts For Your Next Test

1. Ultramafic rocks typically have a silica content of less than 45%, which is significantly lower than that of mafic rocks.
2. The presence of olivine in ultramafic rocks gives them a distinctive green color, often seen in peridotite and similar formations.
3. Ultramafic magmas are believed to originate from the Earth's mantle, indicating that they are closely related to the processes occurring deep within the Earth.
4. Due to their high density, ultramafic rocks are commonly found in tectonic settings where mantle material is brought closer to the surface.
5. These rocks can play a crucial role in understanding plate tectonics and the formation of oceanic crust, as they often form at mid-ocean ridges.

Review Questions

• How does the composition of ultramafic magma differ from mafic magma, and what implications does this have for their physical properties?
  • Ultramafic magma has a higher proportion of magnesium and iron with lower silica content compared to mafic magma. This difference in composition leads to distinct physical properties such as higher density and higher melting temperatures. The low silica content in ultramafic magma results in a more fluid-like behavior during eruptions, which can affect volcanic activity and the types of rocks formed during solidification.
• Discuss the significance of peridotite as an ultramafic rock in understanding the Earth's mantle composition.
  • Peridotite is a key ultramafic rock that provides valuable insights into the Earth's mantle, as it is primarily composed of olivine. Studying peridotite helps scientists infer the chemical and physical conditions present deep within the Earth. Since peridotite represents the predominant rock type in the upper mantle, its analysis can reveal important information about mantle dynamics, the formation of magma, and processes related to plate tectonics.
• Evaluate the role of ultramafic rocks in plate tectonics and how they contribute to our understanding of geological processes.
  • Ultramafic rocks play a crucial role in plate tectonics by providing evidence for mantle dynamics and the movement of tectonic plates. Their presence at mid-ocean ridges suggests active mantle upwelling and magmatism, leading to new oceanic crust formation. By studying ultramafic compositions and their behavior during tectonic processes, geologists can better understand phenomena such as subduction zones, volcanic activity, and the recycling of crustal materials back into the mantle, thereby enhancing our knowledge of geological processes on Earth.

Related terms

Mafic: A term for igneous rocks that are rich in magnesium and iron but contain more silica than ultramafic rocks, often resulting in a darker color.

Peridotite:

An ultramafic rock composed mainly of olivine, often found in the Earth's mantle and significant for understanding mantle composition.

Silica:

A chemical compound (SiO₂) that is a major component of many igneous rocks, influencing their properties and classification.