Modification of Caloris ejecta blocks by long-lived mass-wasting: A volatile-driven process?
Modification of Caloris ejecta blocks by long-lived mass-wasting: A volatile-driven process?
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通过长期大量消耗来改变热量喷射物块：挥发性驱动的过程？
DOI：
10.1016/j.epsl.2020.116519
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发表时间：
2020
影响因子：
5.3
通讯作者：
Wright J
中科院分区：
文献类型：
--
作者：
Wright J
Caloris盆地是水星上最大的保存完好的撞击盆地。因此，Caloris喷出物为我们提供了一个利用遥感研究水星深层内部物质的机会。我们已经对环卡路里旋钮的地貌、颜色、分布和侧面坡度进行了观察。我们的观察表明，这些环卡路里旋钮是卡路里撞击产生的改良喷出物块。高分辨率的信使号图像显示，旋钮是圆锥形的，与周围的平原相比，相对没有陨石坑，这意味着旋钮已经经历了表面重塑。我们已经观察到物质脱落的旋钮叠加的冲击陨石坑，明显晚于卡路里的影响，这需要一些旋钮修改已经更新。我们观察到水星表面的凹陷，一般认为是由挥发性损失引起的，与几个旋钮密切相关，这表明许多旋钮含有挥发性物质，旋钮的修改可能会延伸到水星的最近过去。我们的测量结果表明，旋钮侧翼通常有1.21 °的斜率，这是陡峭的一个土堆的松散的材料，最初侵位3.8 Ga。球的圆锥形，陡峭的斜坡，缺乏重叠的火山口的旋钮，和旋钮叠加关系与其他地貌表明，任意原始形状的卡路里喷出物块被修改成目前的形状，长期生活的质量浪费。大规模的浪费必须占主导地位的影响园艺，这将产生圆顶形态。我们认为，质量浪费可能是由挥发性损失驱动的，以类似于陆地地形称为“臼齿”。如果环卡路里旋钮类似于臼齿，那么它们代表了水星上迄今为止没有记录的地形和过程，这对行星内部的挥发性成分有影响。因此，这些旋钮是BepiColombo的主要目标，它可以搜索旋钮中的新故障和波动性暴露。
The Caloris basin is the largest well-preserved impact basin on Mercury. As such, Caloris ejecta afford us an opportunity to study material from Mercury's deep interior with remote sensing. We have made observations of the geomorphology, colour, distribution, and flank slopes of the circum-Caloris knobs. Our observations suggest that these circum-Caloris knobs are modified ejecta blocks from the Caloris impact. High-resolution MESSENGER images show that knobs are conical and relatively uncratered compared with the surrounding plains, which implies the knobs have undergone resurfacing. We have observed material that has sloughed off knobs superposing impact craters that demonstrably postdate the Caloris impact, which requires some knob modification to have been more recent. We have observed hollows, depressions in Mercury's surface generally believed to have been caused by volatile-loss, on and closely associated with several knobs, which indicates that many knobs contain volatile material and that knob modification could extend into Mercury's recent past. Our measurements show that knob flanks typically have slopes of ∼21°, which is steep for a mound of unconsolidated material that was originally emplaced ∼3.8 Ga. The conical shape of knobs, their steep slopes, the dearth of superposed craters on knobs, and knob superposition relationships with other landforms suggest that Caloris ejecta blocks of arbitrary original shape were modified into their present shapes by long-lived mass-wasting. Mass-wasting must have dominated over impact gardening, which would have produced domal morphologies only. We suggest that mass-wasting was probably driven by volatile-loss, in a manner analogous to terrestrial landforms called ‘molards’. If the circum-Caloris knobs are analogous to molards, then they represent a landform and a process hitherto undocumented on Mercury, with implications for the volatile content of the planet's interior. These knobs therefore are prime targets for BepiColombo, which could search for fresh failures and volatile exposures in the knobs.
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