Tschauner Oliver, Asimow Paul D, Kostandova Natalya, Ahrens Thomas J, Ma Chi, Sinogeikin Stanislas, Liu Zhenxian, Fakra Sirine, Tamura Nobumichi
High Pressure Science and Engineering Center, Department of Physics, University of Nevada, Las Vegas, NV 89154, USA.
Proc Natl Acad Sci U S A. 2009 Aug 18;106(33):13691-5. doi: 10.1073/pnas.0905751106. Epub 2009 Aug 10.
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.
我们在一次冲击实验的回收产物中观察到了微米级的瓦兹利石颗粒，瓦兹利石是（Mg，Fe）₂SiO₄的一种高压相。我们推断这些颗粒是在小于1微秒的时间间隔内从冲击产生的熔体中结晶出来的，这是我们的实验达到并维持足以使该相稳定的压力的最长时间。这种快速的晶体生长速率（约1米/秒）表明，与之前对强冲击陨石中冲击熔体脉中高压相出现情况的研究结论相反，冲击事件期间熔体中高压相的生长不受扩散控制。在晶体生长过程中，一定有另一个过程，比如微湍流输运，在起作用。这一结果意味着，在冲击陨石中使高压相结晶所需的时间可能对应于直径1 - 5米的物体之间撞击所达到的冲击压力持续时间，而不是像之前推断的那样约为直径1 - 5千米的物体之间撞击所达到的冲击压力持续时间。这些结果还可能为通过冲击回收合成一些高价值的高压相提供另一条途径。
