Ultrafast growth of wadsleyite in shock-produced melts and its implications for early solar system impact processes.
We observed micrometer-sized grains of wadsleyite, a high-pressure phase of (Mg,Fe)(2)SiO(4,) in the recovery products of a shock experiment. We infer these grains crystallized from shock-generated melt over a time interval of <1 micros, the maximum time over which our experiment reached and sustained pressure sufficient to stabilize this phase. This rapid crystal growth rate (approximately 1 m/s) suggests that, contrary to the conclusions of previous studies of the occurrence of high-pressure phases in shock-melt veins in strongly shocked meteorites, the growth of high-pressure phases from the melt during shock events is not diffusion-controlled. Another process, such as microturbulent transport, must be active in the crystal growth process. This result implies that the times necessary to crystallize the high-pressure phases in shocked meteorites may correspond to shock pressure durations achieved on impacts between objects 1-5 m in diameter and not, as previously inferred, approximately 1-5 km in diameter. These results may also provide another pathway for syntheses, via shock recovery, of some high-value, high-pressure phases.
Tschauner
Oliver
O
High Pressure Science and Engineering Center, Department of Physics, University of Nevada, Las Vegas, NV 89154, USA.
Asimow
Paul D
PD
Kostandova
Natalya
N
Ahrens
Thomas J
TJ
Ma
Chi
C
Sinogeikin
Stanislas
S
Liu
Zhenxian
Z
Fakra
Sirine
S
Tamura
Nobumichi
N
D003460:Crystallization; D008027:Light; D008670:Metals / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning / Q000379:methods; D011312:Pressure; D012542:Scattering, Radiation; D017640:Silicates / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry*; D012984:Software; D016082:Solar System; D013055:Spectrophotometry, Infrared / Q000379:methods; D017356:Synchrotrons; D013696:Temperature; D014961:X-Ray Diffraction
D008670:Metals; D017640:Silicates; D012825:Silicon