Ultrafast olivine-ringwoodite transformation during shock compression

Area of Science:

• Mineralogy
• Planetary Science
• High-pressure Physics

Background:

• Meteorites contain high-pressure mineral polymorphs, indicating past hypervelocity collisions.
• Previous understanding suggested these transformations required seconds, linked to large asteroid impacts.
• The exact mechanisms and timescales of these mineral transformations were experimentally unverified.

Purpose of the Study:

• To experimentally investigate the mechanisms of mineral transformation under shock compression.
• To determine if high-pressure polymorphs like ringwoodite can form on shorter timescales.
• To re-evaluate the size of celestial bodies capable of producing these shock events.

Main Methods:

• Shock compression of an olivine crystal using a focused high-power laser pulse.
• Time-resolved analysis of the transformation process using femtosecond X-ray free electron laser (XFEL) diffractometry.
• Investigation of nanosecond-timescale shock-induced mineral phase transitions.

Main Results:

• Observed a nanosecond transformation mechanism leading to the formation of ringwoodite.
• Ringwoodite formation occurred via a rapid, diffusionless process.
• The transformation is significantly faster than previously hypothesized.

Conclusions:

• Ringwoodite can form through a much faster, diffusionless mechanism than previously assumed.
• This mechanism allows for ringwoodite formation from collisions involving smaller asteroids (metre to submetre scale).
• Even meteorites appearing unshocked may contain evidence of high-pressure states from past impacts.