Abstract

We present the results of geological and morphological analysis of LROC NAC images of a small volcanic crater Ina, D-shaped in plan view (2.9 × 1.9 km), and its immediate surroundings. This crater is located at the top of a very gently sloping shield volcano, the slopes of which, judging by the density of superimposed small craters, were formed ~3.5 Ga ago. Inside the crater there is a region with uneven relief and low hills, the density of small craters on which corresponds to an age of <100 Ma. In a number of works, the formations inside the Ina crater are considered to be manifestations of very young volcanism, while in other works, hills with an apparent age of <100 Ma are considered to be composed of “magmatic foam” such as massive pumice, which could affect the formation of small craters on them, reducing their diameters and thereby underestimating their measured spatial density. Accordingly, the Ina crater may be ancient and have the same age as the slopes of the shield volcano. In this paper, we studied the degree of morphological “freshness” of formations inside the Ina structure and compared the morphology of small craters superimposed on the hills inside Ina and on the slopes of the shield volcano adjacent to the Ina structure. In addition, model calculations of the thickness of the regolith layer for the cases of a “normal” target and a target consisting of “magmatic foam” have been performed. It is shown that the morphological freshness of the formations inside the Ina crater does not agree with the assumption about the ancientry of this crater, and morphologically “fresh” small craters on the hills inside Ina barely differ from those on the slopes of the shield volcano. These observations appear to contradict the “magmatic foam” hypothesis and support the conclusion that Ina’s structure is young.

中文翻译：

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月球陨石坑伊娜：陨石坑内地貌形态分析

摘要

我们介绍了一个小型火山口伊纳（Ina）的LROC NAC图像的地质和形态分析结果，该伊纳在平面图（2.9×1.9 km）及其附近环境中呈D形。这个火山口位于一个非常缓慢倾斜的盾构火山的顶部，根据叠加的小火山口的密度判断，其火山形成的坡度约为3.5 Ga。陨石坑内有一个凹凸不平，低丘的区域，小陨石坑的密度对应于<100 Ma的年龄。在许多作品中，伊纳火山口内的地层被认为是非常年轻的火山作用的表现，而在其他作品中，表观年龄小于100 Ma的山丘被认为是由“岩浆泡沫”组成的，例如块状浮石。 ，这可能会影响小火山口的形成，减小其直径，从而低估了它们测得的空间密度。因此，伊那火山口可能很古老，并且年龄与盾构火山的山坡相同。在本文中，我们研究了伊纳（Ina）结构内部地层的形态“新鲜度”，并比较了伊纳（Ina）内部丘陵和与伊纳（Ina）结构相邻的盾构火山斜坡上叠加的小火山口的形态。另外，对于“正常”靶和由“岩浆泡沫”构成的靶，进行了硬石膏层厚度的模型计算。结果表明，伊纳火山口内部地层的形态新鲜度与该火山口的古老性假设不符，在伊纳（Ina）内山丘上，形态上“新鲜”的小火山口与盾构火山山坡上的火山口几乎没有什么不同。这些观察似乎与“岩浆泡沫”假说相矛盾，并支持伊纳结构年轻的结论。