When
3:30 p.m., Sept. 20, 2011
Where
Kuiper Space Sciences 308
Dr. Thomas Sharp
Professor at Arizona State University
"Shock Metamorphism in Chondrites: Constraints on Impact History of L chondrites"
Meteorites are fragments of planets and asteroids that provide insight into planet formation and solar system processes. The assembly of planets and asteroids involved hyper-velocity collisions that are recorded in meteorites as shock metamorphism. Shock features include deformation, phase transformations, recrystallization, melting and crystallization. These shock effects have been used to estimate shock pressures by comparing them to features produced in shock-recovery experiments. The shock classification and pressure-calibration developed by Stoffler et. al (1991), which has been widely adopted by meteoriticists, implies that highly-shocked chondrites have experienced shock pressures from 50 to 90 GPa, suggesting high impact velocities between asteroids. Localized melting in shocked meteorites results in shock-melt veins and pockets that commonly crystallize at high pressure and record the pressure-temperature conditions of melt crystallization. The shock pressures estimated from melt crystallization are 18 - 25 GPa, which are significantly lower than those based on shock recovery experiments. We have used melt-vein crystallization and solid-state phase transformations to estimate shock pressures and durations. We find that the maximum shock pressure recorded in melt-vein crystallization is 26 GPa and the shock duration can be up to several seconds. Modeling the shock associated with various impact scenarios, we infer that the impact on the L-chondrite parent body at about 500 Ma involved a large impacting body (2- 10 km) and modest relative velocity (3 to ~ 7 km/s).
Professor at Arizona State University
"Shock Metamorphism in Chondrites: Constraints on Impact History of L chondrites"
Meteorites are fragments of planets and asteroids that provide insight into planet formation and solar system processes. The assembly of planets and asteroids involved hyper-velocity collisions that are recorded in meteorites as shock metamorphism. Shock features include deformation, phase transformations, recrystallization, melting and crystallization. These shock effects have been used to estimate shock pressures by comparing them to features produced in shock-recovery experiments. The shock classification and pressure-calibration developed by Stoffler et. al (1991), which has been widely adopted by meteoriticists, implies that highly-shocked chondrites have experienced shock pressures from 50 to 90 GPa, suggesting high impact velocities between asteroids. Localized melting in shocked meteorites results in shock-melt veins and pockets that commonly crystallize at high pressure and record the pressure-temperature conditions of melt crystallization. The shock pressures estimated from melt crystallization are 18 - 25 GPa, which are significantly lower than those based on shock recovery experiments. We have used melt-vein crystallization and solid-state phase transformations to estimate shock pressures and durations. We find that the maximum shock pressure recorded in melt-vein crystallization is 26 GPa and the shock duration can be up to several seconds. Modeling the shock associated with various impact scenarios, we infer that the impact on the L-chondrite parent body at about 500 Ma involved a large impacting body (2- 10 km) and modest relative velocity (3 to ~ 7 km/s).
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