Petrographic investigation of shatter cone melt films recovered from MEMIN impact experiments in sandstone and iSALE modeling of their formation boundary conditions
Petrographic investigation of shatter cone melt films recovered from MEMIN impact experiments in sandstone and iSALE modeling of their formation boundary conditions
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对砂岩 MEMIN 冲击实验中恢复的破碎锥熔体膜进行岩相学研究，并对其地层边界条件进行 iSALE 建模
DOI：
10.1111/maps.13179
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发表时间：
2018
影响因子：
2.2
通讯作者：
Kenkmann T.
中科院分区：
文献类型：
--
作者：
Wilk J;Hamann C;Fazio A;Hecht L;Langenhorst F.;Kenkmann T.
破碎锥是识别陨石撞击坑的诊断工具。它们在现场是明确可识别的，并且是唯一的宏观冲击变形特征。然而，物理边界条件和确切的形成机制仍然是一个争论的主题。在破碎锥表面上发现的熔体膜可以在其形成期间或之后立即允许压力-温度条件的约束。在MEMIN研究小组的框架内，我们从超高速撞击实验的喷出物中回收了24个碎裂锥碎片。在这里，我们专注于硅酸盐熔体膜（现在淬火成玻璃），在实验中形成的破碎锥表面与20-80厘米大小的砂岩目标，由铝和铁陨石弹丸的5和12毫米直径的速度分别为7.0和4.6公里秒-1的冲击。回收的破碎锥碎片大小从1.2到9.3毫米不等。它们显示出轻微弯曲的条纹状表面和顶角为36°-52°的圆锥形几何形状。这些碎片是从实验中回收的，峰值压力从46到86 GPa不等，并从0.38陨石坑半径内的区域发出。基于iSale建模和岩相学研究，破碎锥材料经历了0.5-5 GPa的低整体冲击压力，而变形显示朝向破碎锥表面急剧增加，导致岩石局部熔融，导致在SEM下可见的泡状和抛光熔体纹理。熔体膜的下表面是破碎和脆性剪切区，表明岩石从破碎锥的锥顶开始运动。熔体膜的涂抹和延伸表明随后的运动方向与粉碎和角砾状剪切区相反。我们认为，记录的剪切纹理和相邻的光滑的熔体膜可以与摩擦熔化，而覆盖的高度泡状的熔体层可能表明快速的压力释放。根据对上覆结构中石英、层状硅酸盐和金红石的熔融和混合的观察，我们推断，震后温度很高，但非常局部，超过2000 °C。破碎锥表面的熔化的上部横切破碎的下部，并伴随着平行于{112}平面的石英中形成的PDF。基于叠印纹理和记录的冲击效应，我们假设破碎锥在冲击加载过程中开始形成，并在卸载过程中保持活跃的断裂面，直到压力释放，并推断破碎锥表面是混合模式I/II断裂面。
Shatter cones are diagnostic for the recognition of meteorite impact craters. They are unambiguously identifiable in the field and the only macroscopic shock deformation feature. However, the physical boundary conditions and exact formation mechanism(s) are still a subject of debate. Melt films found on shatter cone surfaces may allow the constraint of pressure–temperature conditions during or immediately after their formation. Within the framework of the MEMIN research group, we recovered 24 shatter cone fragments from the ejecta of hypervelocity impact experiments. Here, we focus on silicate melt films (now quenched to glass) found on shatter cone surfaces formed in experiments with 20–80 cm sized sandstone targets, impacted by aluminum and iron meteorite projectiles of 5 and 12 mm diameter at velocities of 7.0 and 4.6 km s−1, respectively. The recovered shatter cone fragments vary in size from 1.2 to 9.3 mm. They show slightly curved, striated surfaces, and conical geometries with apical angles of 36°–52°. The fragments were recovered from experiments with peak pressures ranging from 46 to 86 GPa, and emanated from a zone within 0.38 crater radii. Based on iSale modeling and petrographic investigations, the shatter coned material experienced low bulk shock pressures of 0.5–5 GPa, whereas deformation shows a steep increase toward the shatter cone surface leading to localized melting of the rock, resulting in both vesicular as well as polished melt textures visible under the SEM. Subjacent to the melt films are zones of fragmentation and brittle shear, indicating movement away from the shatter cone apex of the rock that surrounds the cone. Smearing and extension of the melt film indicates subsequent movement in opposite direction to the comminuted and brecciated shear zone. We believe the documented shear textures and the adjacent smooth melt films can be related to frictional melting, whereas the overlying highly vesiculated melt layer could indicate rapid pressure release. From the observation of melting and mixing of quartz, phyllosilicates, and rutile in this overlying texture, we infer high, but very localized postshock temperatures exceeding 2000 °C. The melted upper part of the shatter cone surface cross‐cuts the fragmented lower section, and is accompanied by PDFs developed in quartz parallel to the {112} plane. Based on the overprinting textures and documented shock effects, we hypothesize shatter cones start to form during shock loading and remain an active fracture surface until pressure release during unloading and infer that shatter cone surfaces are mixed mode I/II fracture surfaces.
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影响因子：
2.2
作者：
Wilk J.;Kenkmann T.
通讯作者：
Kenkmann T.
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DOI：
--
发表时间：
2016
期刊：
影响因子：
--
作者：
J. Wilk;C. Hamann;T. Kenkmann;L. Hecht
通讯作者：
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DOI：
--
发表时间：
2005
期刊：
影响因子：
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作者：
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