Omphacite

Definition

Omphacite is a clinopyroxene mineral that is commonly found in high-pressure metamorphic rocks, especially eclogites. This mineral is significant because it forms under specific pressure-temperature conditions that are characteristic of certain metamorphic facies, particularly in subduction zones. Its presence indicates the unique conditions that lead to the transformation of rocks under intense geological processes.

5 Must Know Facts For Your Next Test

1. Omphacite typically forms at high pressures, generally above 2 GPa, which corresponds to depths of about 60 kilometers in the Earth's crust.
2. The chemical composition of omphacite often includes significant amounts of jadeite and diopside, giving it a unique character among pyroxenes.
3. It plays a critical role in understanding the geological history and tectonic processes involved in subduction zones and continental collision.
4. Omphacite is used as an indicator mineral for identifying eclogite-facies metamorphism and can provide insights into the thermal evolution of subducted materials.
5. The study of omphacite can also contribute to understanding the dynamics of plate tectonics and the formation of mountain ranges.

Review Questions

• How does omphacite's formation relate to the geological processes occurring in subduction zones?
  • Omphacite forms in subduction zones where high-pressure conditions prevail due to one tectonic plate being forced beneath another. This process leads to the transformation of mafic rocks into eclogite, where omphacite becomes a dominant mineral. The study of omphacite helps geologists understand the extreme conditions within these zones, shedding light on the metamorphic processes that occur during plate interactions.
• Discuss how omphacite contributes to our understanding of metamorphic facies and their corresponding pressure-temperature conditions.
  • Omphacite is a key mineral in identifying eclogite facies, which are associated with high-pressure metamorphism. By studying omphacite and its associated minerals, geologists can better understand the specific pressure-temperature conditions under which these rocks form. This knowledge helps refine models of metamorphic processes and provides insights into the broader context of tectonic activities influencing rock formation.
• Evaluate the implications of finding omphacite in a rock sample regarding its metamorphic history and potential tectonic environment.
  • The presence of omphacite in a rock sample suggests a complex metamorphic history indicative of high-pressure conditions typical in subduction zones. This finding implies that the rock may have originated from a basaltic source and undergone significant transformation due to tectonic activity. Understanding where and how omphacite forms can reveal important details about past geological events, helping researchers piece together the history of tectonic movements and related metamorphic processes.

Related terms

Eclogite: A dense, high-pressure metamorphic rock primarily composed of garnet and omphacite, formed from basalt or other mafic rocks in subduction environments.

Metamorphic Facies: Groups of metamorphic rocks that share similar mineral assemblages and are formed under specific pressure and temperature conditions.

Subduction Zone:

An area where one tectonic plate moves under another, leading to high pressures and temperatures that contribute to the formation of metamorphic rocks like eclogite.