Shock Metamorphism

Definition

Shock metamorphism refers to the dramatic physical and chemical changes that occur in rocks and minerals when they are subjected to the intense pressure and heat generated by the impact of a meteorite or asteroid. This process can transform the target materials in various ways, creating distinctive features that are characteristic of impact events.

5 Must Know Facts For Your Next Test

1. Shock metamorphism can produce a wide range of diagnostic features in target rocks, including shatter cones, impact glass, and the formation of high-pressure mineral phases.
2. The degree of shock metamorphism observed in rocks can provide insights into the intensity of the impact event, with higher levels of shock indicating more energetic collisions.
3. Shock metamorphism can occur over a wide range of pressures, from just a few gigapascals (GPa) to over 100 GPa, depending on the size and velocity of the impacting object.
4. The presence of planar deformation features (PDFs) in quartz grains is considered one of the most reliable indicators of shock metamorphism and the occurrence of an impact event.
5. Shock metamorphism can also lead to the melting and vaporization of target materials, creating distinctive features like impact glass, tektites, and impact craters.

Review Questions

• Explain how the intensity of an impact event can be inferred from the degree of shock metamorphism observed in the target rocks.
  • The degree of shock metamorphism observed in rocks can provide insights into the intensity of the impact event that caused it. Rocks subjected to higher pressures and temperatures will exhibit more severe shock features, such as the development of high-pressure mineral phases, more extensive planar deformation features (PDFs) in quartz, and the melting or vaporization of target materials. The presence and characteristics of these diagnostic shock metamorphic features can be used to estimate the energy and force of the impact, with more intense impacts producing higher levels of shock metamorphism.
• Describe the role of planar deformation features (PDFs) in quartz as an indicator of shock metamorphism and impact events.
  • Planar deformation features (PDFs) in quartz are considered one of the most reliable indicators of shock metamorphism and the occurrence of an impact event. These microscopic, parallel fractures form in quartz grains under the extreme pressures generated by a meteorite or asteroid impact. The presence and characteristics of PDFs, such as their orientation, spacing, and the number of sets, can provide information about the intensity of the shock wave and the pressure conditions experienced by the target rocks. The identification of PDFs in quartz is a key diagnostic tool used by geologists to identify and study impact structures, as these features are unique to the shock metamorphism caused by impact events and cannot be produced by other geological processes.
• Analyze how the melting and vaporization of target materials due to shock metamorphism can contribute to the formation of distinctive impact features, such as impact glass and tektites.
  • The intense pressure and heat generated during an impact event can lead to the melting and vaporization of target materials, creating distinctive features like impact glass and tektites. Impact glass is formed when the target rocks are rapidly melted and then quenched, preserving the glassy texture. Tektites are natural glass objects that are ejected from the impact site and can be found over a wide geographic area. The formation of these features is a direct result of the shock metamorphism experienced by the target rocks, as the extreme conditions of the impact can transform the mineral composition and physical properties of the materials. The study of impact glass and tektites can provide valuable insights into the nature and intensity of the impact event, as well as the processes of shock metamorphism that occur during the collision.

Related terms

Shockwave: The powerful compressional wave that radiates outward from the point of impact, transmitting the tremendous energy released during an impact event.

Planar Deformation Features (PDFs): Microscopic, parallel fractures that form in quartz and other minerals under the extreme pressures of a meteorite impact, serving as a diagnostic indicator of shock metamorphism.

Shocked Quartz: Quartz grains that have been subjected to the immense pressures of an impact, resulting in the development of unique features like PDFs and the transformation of the crystal structure.