Survival of fossilised diatoms and forams in hypervelocity impacts with peak shock pressures in the 1-19 GPa range
Survival of fossilised diatoms and forams in hypervelocity impacts with peak shock pressures in the 1-19 GPa range
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DOI：
10.1016/j.icarus.2017.02.028
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发表时间：
2017-07-01
期刊：
影响因子：
3.2
通讯作者：
Yolland, L.
中科院分区：
文献类型：
--
作者：
Burchell, M. J.;Harriss, K. H.;Yolland, L.
此前，已有研究表明，埋在冰层中的硅藻化石可以在速度高达5公里的S(-1)和峰值冲击压力高达12 GPA的情况下幸存下来。在这里，我们用一种不同的技术证实了这些结果，在撞击速度为2-6公里的S(-1)的情况下，硅藻被携带在液体水悬浮液中。这相当于3.8-19.8 Gpa的峰值冲击压力。我们还报告了用有孔板进行的类似实验的结果，冲击速度分别为4.67公里S(-1)(在水中携带时)和4.73公里S(-1)(在冰中携带时)，对应的峰值冲击压力分别为11.6和13.1GPa.在所有情况下，我们再次发现可识别的碎片存活下来，平均碎片大小约为20-25微米。我们将我们的结果与巨大撞击地球的喷射物在随后撞击月球时所经历的峰值冲击压力进行了比较。我们发现，如果地球喷射物是一种软岩(砂岩)，那么98%的地球喷射物对月球的影响都会经历低于20 GPA的峰值压力。如果喷出的陨石是坚硬的岩石(花岗岩)，这一比例将下降到82%。这假设撞击在坚实的月球表面上。如果我们将表面近似为一个松散的风化层，超过99%的撞击涉及峰值冲击压力低于20 Gpa。无论哪种方式，结果都表明，撞击月球的相当大一部分陆地陨石将以峰值冲击压力这样做，在我们的实验中，峰值冲击压力允许可识别的化石碎片存活。(C)2017 Elsevier Inc.保留所有权利。
Previously it has been shown that diatom fossils embedded in ice could survive impacts at speeds of up to 5 km s(-1) and peak shock pressures up to 12 GPa. Here we confirm these results using a different technique, with diatoms carried in liquid water suspensions at impact speeds of 2-6 km s(-1). These correspond to peak shock pressures of 3.8-19.8 GPa. We also report on the results of similar experiments using forams, at impact speeds of 4.67 km s(-1) (when carried in water) and 4.73 km s(-1) (when carried in ice), corresponding to peak shock pressures of 11.6 and 13.1 GPa respectively. In all cases we again find survival of recognisable fragments, with mean fragment size of order 20-25 mu m. We compare our results to the peak shock pressures that ejecta from giant impacts on the Earth would experience if it subsequently impacted the Moon. We find that 98% of impacts of terrestrial ejecta on the Moon would have experienced peak pressures less than 20 GPa if the ejecta were a soft rock (sandstone). This falls to 82% of meteorites if the ejecta were a hard rock (granite). This assumes impacts on a solid lunar surface. If we approximate the surface as a loose regolith, over 99% of the impacts involve peak shock pressures below 20 GPa. Either way, the results show that a significant fraction of terrestrial meteorites impacting the Moon will do so with peak shock pressures which in our experiments permit the survival of recognisable fossil fragments. (C) 2017 Elsevier Inc. All rights reserved.