Diaplectic quartz glass and SiO2 melt experimentally generated at only 5 GPa shock pressure in porous sandstone: Laboratory observations and meso-scale numerical modeling
Diaplectic quartz glass and SiO2 melt experimentally generated at only 5 GPa shock pressure in porous sandstone: Laboratory observations and meso-scale numerical modeling
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DOI：
10.1016/j.epsl.2013.09.021
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发表时间：
2013-12
影响因子：
5.3
通讯作者：
A. Kowitz;N. Güldemeister;W. Reimold;R. Schmitt;K. Wünnemann
中科院分区：
文献类型：
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作者：
A. Kowitz;N. Güldemeister;W. Reimold;R. Schmitt;K. Wünnemann
冲击恢复实验和数值模拟的冲击变形在低压范围从2.5到17.5 GPa的干燥，多孔的Seeberger砂岩相结合，提供了新的，重要的见解方面的不均匀性的冲击分布在这样重要的，上地壳的材料，迄今为止没有压力校准计划的冲击变质。我们发现在2.5GPa的冲击压力下孔隙已经完全闭合。在冲击实验中，石英单晶在5GPa压力下开始转变为透晶石英玻璃和/或SiO2熔体，而在冲击压力分别为30-35 GPa和1.45 GPa的情况下没有观察到这些效应。透晶玻璃或熔体的外观并不局限于直接低于冲击表面的区域，而是与更宽区域中的孔的出现有关。从0.03vol. %开始，随着冲击压力的增加，这些相的结合量明显增加在5 GPa至1080 vol. % 17.5 GPa。根据以前对陨石坑自然冲击的可可尼诺砂岩中二氧化硅相的冲击分类，该分类基于可可尼诺砂岩Hugoniot曲线的不同斜率，我们的观察使我们能够建立一个与Kieffer（1971）的渐进冲击变质分类的冲击阶段1b-4相一致的多孔砂岩的冲击压力分类。尺度解释了多孔材料和单晶石英中冲击变形的差异，与我们的实验结果一致。它证实了孔隙空间在低标称压力下完全塌陷，并表明孔隙空间塌陷导致局部压力放大，可能超过初始压力的4倍。这为在低冲击压力实验中观察到的透晶石英玻璃和钙钛矿的形成提供了解释。数值模型预测的SiO2熔体的量类似于在冲击实验中观察到的。这也表明，数值模型是必不可少的，以提供超出实验能力的信息。
A combination of shock recovery experiments and numerical modeling of shock deformation in the low pressure range from 2.5 to 17.5 GPa in dry, porous Seeberger sandstone provides new, significant insights with respect to the heterogeneous nature of shock distribution in such important, upper crustal material, for which to date no pressure-calibrated scheme for shock metamorphism exists. We found that pores are already completely closed at 2.5 GPa shock pressure. Whole quartz grains or parts of them are transformed to diaplectic quartz glass and/or SiO2melt starting already at 5 GPa, whereas these effects are not observed below shock pressures of 30–35 and ∼45 GPa, respectively, in shock experiments with quartz single crystals. The appearance of diaplectic glass or melt is not restricted to the zone directly below the impacted surface but is related to the occurrence of pores in a much broader zone. The combined amount of these phases increases distinctly with increasing shock pressure from 0.03 vol.% at 5 GPa to ∼80 vol.% at 17.5 GPa. In accordance with a previous shock classification for silica phases in naturally shocked Coconino sandstone from Meteor Crater that was based on varied slopes of the Coconino sandstone Hugoniot curve, our observations allow us to construct a shock pressure classification for porous sandstone consistent with shock stages 1b–4 of the progressive shock metamorphism classification of Kieffer (1971).Numerical modeling at the meso-scale provides the explanation for the discrepancy of shock deformation in porous material and single-crystal quartz, in keeping with our experimental results. It confirms that pore space is completely collapsed at low nominal pressure and demonstrates that pore space collapse results in localized pressure amplification that can exceed 4 times the initial pressure. This provides an explanation for the formation of diaplectic quartz glass and lechatelierite as observed in the low-shock-pressure experiments. The numerical models predict an amount of SiO2melt similar to that observed in the shock experiments. This also shows that numerical models are essential to provide information beyond experimental capabilities.