The impacted Martian crust: structure, hydrology, and some geologic implications.
The impacted Martian crust: structure, hydrology, and some geologic implications.
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受影响的火星地壳：结构、水文学和一些地质意义。
DOI：
10.1029/jb094ib12p17359
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发表时间：
1989
影响因子：
--
通讯作者：
Kenneth L. Tanaka
中科院分区：
文献类型：
--
作者：
D. J. Mackinnon;Kenneth L. Tanaka
我们认为，遭受严重轰炸的火星地壳通常由10公里厚的高渗透性、破碎的基岩带组成，上面覆盖着1至2公里厚、相对不透水的喷射层。对地面撞击和爆炸坑的地震、钻探和观测测量表明，地下岩石强烈破裂成米大小(或更大)的块体。对地球和月球陨石坑的重力测量表明，在底部基岩的上部几公里处发生了百分之几的膨胀。这些测量表明，裂隙的火星基岩可能具有大约1%的开放裂隙孔隙度和至少103达里尔的渗透率；由于裂隙强度的降低和岩石静压力的增加，这些值将随着深度的增加而减小。理论撞击破碎和混合模型以及实验室和现场研究表明，撞击喷出物由混合良好、分选较差的碎屑组成，服从幂函数分布。根据这些分布、堆积理论、实验关系和对相似物质的测量，我们估计喷出带内未蚀变喷出物的平均孔隙度为10-20%，其最大渗透率约为10−2达西。随后的胶结作用和挤压作用使喷出物的变化降低了孔隙度和渗透率，而局部压裂作用则增加了孔隙度和渗透率。粉碎可能会产生大量粘土大小的物质，这些物质可能有效地保留水或冰，并增加赤道地区的地面冰保留。我们的模型与观测到的火星地壳中1到3公里深的机械不连续以及疏松喷射物的侵蚀敏感性和其他过程是一致的。我们进一步提出，由喷射物组成的泥石流和随后的灾难性洪水可以解释克赖斯地区流出水道的发展，其用水量比洪水单独需要的要少得多。
We propose that the heavily bombarded Martian crust generally consists of a 10-km-thick zone of highly permeable, fractured basement rock overlain by a 1- to 2-km-thick, relatively impermeable ejecta zone. Seismic, drill core, and observational measurements of terrestrial impact and explosion craters demonstrate that the subjacent rocks are intensely fractured into meter-sized (or larger) blocks. Gravity measurements over terrestrial and lunar craters indicate that bulking of a few percent occurred in the upper few kilometers of the underlying bedrock. These measurements suggest that fractured Martian basement rocks may have an open fracture porosity of about 1% and permeabilities of at least 103 darcies; these values would decrease with depth due to decreasing fracture intensity and increasing lithostatic pressure. Theoretical impact fragmentation and mixing models and laboratory and field studies indicate that impact ejecta are composed of well-mixed, poorly sorted clasts that follow power law distributions. On the basis of these distributions, packing theory, experimental relations, and measurements on analogous materials, we estimate that the average porosity of unaltered ejecta within the ejecta zone is 10–20% and their maximum permeability is about 10−2 darcy. Subsequent alteration of ejecta by cementation and compression may reduce porosity and permeability, whereas local fracturing may increase them. Comminution may produce an abundance of clay-sized material that may effectively retain water or ice and increase ground ice retention in equatorial areas. Our model is consistent with observed 1- to 3-km-deep mechanical discontinuities in the Martian crust and the susceptibility to erosion of unconsolidated ejecta by sapping and other processes. We further propose that debris flows made up of ejecta and followed by catastrophic floods may explain the development of Chryse region outflow channels with much less water than was required by flooding alone.