High‐resolution studies of double‐layered ejecta craters: Morphology, inherent structure, and a phenomenological formation model
High‐resolution studies of double‐layered ejecta craters: Morphology, inherent structure, and a phenomenological formation model
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双层喷射物陨石坑的高分辨率研究：形态学、固有结构和唯象形成模型
DOI：
10.1111/maps.12416
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发表时间：
2014
影响因子：
2.2
通讯作者：
Kenkmann T.
中科院分区：
文献类型：
--
作者：
Wulf G;Kenkmann T.
在富含挥发性物质的环境中，撞击坑的喷出物覆盖层通常具有特征性的分层喷出物形态。所谓的双层喷出物（DLE）陨石坑的特征是具有不同形态的两个喷出物层。对高分辨率图像数据的分析，特别是HiRISE和CTX，为DLE陨石坑的形成提供了新的见解。一个新的现象学挖掘和喷出物侵位模型DLE陨石坑提出了一个详细的案例研究的基础上，火星陨石坑Steinheim-一个保存完好的DLE陨石坑和其他DLE陨石坑的研究。观测结果表明，外喷出物层是作为中间和远端喷出物，在着陆后以碎片雪崩或（如果充满水）碎片流模式向外传播，超越先前形成的二级陨石坑。相比之下，内喷出物层是由近端喷出物沉积物在就位阶段的平移滑动形成的，该平移滑动超出并覆盖外喷出物层的部分。根据我们的模型，火星上的DLE陨石坑是撞击事件进入岩石/冰混合物的结果，该混合物产生大量冲击诱导的蒸发和地面冰的融化，导致高喷射角度，近端着陆位置，以及远侧部分相对潮湿（以液体形式的水）成分的喷出物幕，而近侧部分则是干燥成分。其结果是，在瞬态火山口边缘，这是由摩擦加热和深度的压力增强引起的喷出物中的冰成分的基础融化，启动了向外定向的火山口边缘材料在平移滑动模式的崩溃。我们的研究结果表明，类似的过程也可能适用于其他具有丰富挥发性环境的行星体，如Ganymede，Europa和地球。
The ejecta blankets of impact craters in volatile‐rich environments often possess characteristic layered ejecta morphologies. The so‐called double‐layered ejecta (DLE) craters are characterized by two ejecta layers with distinct morphologies. The analysis of high‐resolution image data, especially HiRISE and CTX, provides new insights into the formation of DLE craters. A new phenomenological excavation and ejecta emplacement model for DLE craters is proposed based on a detailed case study of the Martian crater Steinheim—a well‐preserved DLE crater—and studies of other DLE craters. The observations show that the outer ejecta layer is emplaced as medial and distal ejecta that propagate outwards in a debris avalanche or (if saturated with water) a debris flow mode after landing, overrunning previously formed secondary craters. In contrast, the inner ejecta layer is formed by a translational slide of the proximal ejecta deposits during the emplacement stage that overrun and superimpose parts of the outer ejecta layer. Based on our model, DLE craters on Mars are the result of an impact event into a rock/ice mixture that produces large amounts of shock‐induced vaporization and melting of ground ice, leading to high ejection angles, proximal landing positions, and an ejecta curtain with relatively wet (in terms of water in liquid form) composition in the distal part versus dryer composition in the proximal part. As a consequence, basal melting of ice components in the ejecta at the transient crater rim, which is induced by frictional heating and the enhanced pressure at depth, initiates an outwards directed collapse of crater rim material in a translational slide mode. Our results indicate that similar processes may also be applicable for other planetary bodies with volatile‐rich environments, such as Ganymede, Europa, and the Earth.
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