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Published 1994 | metadata_only
Book Section - Chapter

Hypervelocity impact: Ejecta velocity, angle, and composition


The low projectile component in tektites in contrast to the high projectile component in the Cretaceous-Tertiary (K-T) boundary clay has prompted a study of hypervelocity target-projectile mixing processes. Results from a 6.4-km/sec impact of a Fe-Ni-PGE alloy projectile (90% Fe) into a Mo target indicate that high-angle (55° to 75°), high-velocity (< 6 km/sec) melted ejecta is relatively projectile-rich, whereas low-angle (10° to 40°), low-velocity ejecta (< 1 km/sec) contains less projectile material and is more enriched in the target component. These results support theoretical predictions. Not predicted by theoretical calculation, but observed here, is a break in the compositional trend such that at angles of ejection between 50° and 70°, the projectile/target ratio in the melted ejecta decreases suddenly with increasing angle, only to rise to very high values at higher angles. It appears that for large-body terrestrial impacts, the composition of the high-angle, high-speed ejecta which reaches stratospheric heights will be critical to sudden changes in global climate and the induced environmental stresses. Application of these results to large impacts such as the K-T boundary event, are expected to provide new data pertinent to physical theories of extinction mechanisms.

Additional Information

© 1994 Geological Society of America. Manuscript accepted by the Society December 28, 1993. M. Long provided technical guidance during preparation and execution of the impact experiment. Paul Carpenter's assistance on the microprobe and SEM and Lindsey Hedges' advice and expertise at mounting and polishing such small samples are gratefully acknowledged. Discussions with P. Wyllie, W. W. Anderson and L. Rowan improved the paper. Support was provided by a NASA grant awarded T. J. Ahrens and an NSERC Postdoctoral Fellowship awarded N. J. Evans. This is Caltech contribution number 5264.

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August 20, 2023
August 20, 2023