Shock Recovery With Decaying Compressive Pulses: Shock Effects in Calcite (CaCO3) Around the Hugoniot Elastic Limit
Shock Recovery With Decaying Compressive Pulses: Shock Effects in Calcite (CaCO3) Around the Hugoniot Elastic Limit
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DOI：
10.1029/2021je007133
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发表时间：
2022-05
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通讯作者：
K. Kurosawa;H. Ono;T. Niihara;T. Sakaiya;T. Kondo;N. Tomioka;T. Mikouchi;H. Genda;Takuya Matsuzaki;M. Kayama;M. Koike;Y. Sano;M. Murayama;W. Satake;T. Matsui
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作者：
K. Kurosawa;H. Ono;T. Niihara;T. Sakaiya;T. Kondo;N. Tomioka;T. Mikouchi;H. Genda;Takuya Matsuzaki;M. Kayama;M. Koike;Y. Sano;M. Murayama;W. Satake;T. Matsui
陨石中矿物的冲击变质作用提供了对古代太阳系的洞察。方解石是碳质球粒陨石中丰富的水蚀变矿物。从小行星Ryugu和Bennu传回的样本预计含有方解石族矿物。尽管硅酸盐中的冲击变质作用已经得到了很好的研究，但关于水蚀变矿物的这类数据却很有限。在这里，我们在千叶理工学院行星探索研究中心利用撞击实验研究了含有大理石的方解石中的冲击波效应。我们用比目标更小的弹丸产生了衰变的压缩脉冲。金属容器便于回收保留撞击前地层的样品。用ISALE冲击物理程序估算了样品中的峰值压力分布。与传统的单轴冲击恢复实验相比，这种方法能够从一次实验中产生经历不同程度变质的冲击颗粒的能力是一个优势。用偏光显微镜和X射线衍射仪对冲击后的样品进行了分析。我们发现，当峰值压力超过3 GPa时，超过一半的方解石颗粒表现出波状消光。这一冲击压力比大理石的Hugoniot弹性极限(HEL)高一个数量级，但接近方解石晶体的HEL，这表明波动消光记录了晶体中位错诱导的塑性变形。最后，我们提出了一种重建陨石母体中方解石颗粒最大深度的策略，如果在Ryugu和Bennu的球粒陨石和/或返回的样品中发现了受冲击的方解石颗粒。
Shock metamorphism of minerals in meteorites provides insights into the ancient Solar System. Calcite is an abundant aqueous alteration mineral in carbonaceous chondrites. Return samples from the asteroids Ryugu and Bennu are expected to contain calcite‐group minerals. Although shock metamorphism in silicates has been well studied, such data for aqueous alteration minerals are limited. Here, we investigated the shock effects in calcite with marble using impact experiments at the Planetary Exploration Research Center of Chiba Institute of Technology. We produced decaying compressive pulses with a smaller projectile than the target. A metal container facilitates recovery of a sample that retains its pre‐impact stratigraphy. We estimated the peak pressure distributions in the samples with the iSALE shock physics code. The capability of this method to produce shocked grains that have experienced different degrees of metamorphism from a single experiment is an advantage over conventional uniaxial shock recovery experiments. The shocked samples were investigated by polarizing microscopy and X‐ray diffraction analysis. We found that more than half of calcite grains exhibit undulatory extinction when peak pressure exceeds 3 GPa. This shock pressure is one order of magnitude higher than the Hugoniot elastic limit (HEL) of marble, but it is close to the HEL of a calcite crystal, suggesting that the undulatory extinction records dislocation‐induced plastic deformation in the crystal. Finally, we propose a strategy to re‐construct the maximum depth of calcite grains in a meteorite parent body, if shocked calcite grains are identified in chondrites and/or return samples from Ryugu and Bennu.