Mud volcanism and morphology of impact craters in Utopia Planitia on Mars: Evidence for the ancient ocean
Mud volcanism and morphology of impact craters in Utopia Planitia on Mars: Evidence for the ancient ocean
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DOI：
10.1016/j.icarus.2013.09.018
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发表时间：
2014-01-15
期刊：
影响因子：
3.2
通讯作者：
Reiss, D.
中科院分区：
文献类型：
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作者：
Ivanov, Mikhail A.;Hiesinger, H.;Reiss, D.
我们对乌托邦平原西南部（北纬20-45度，东经100-120度）的单元和结构的性质、相对和绝对模型年龄进行了详细的地质测绘和解释，结果表明：(I)由北大陆单元（VB）物质掩埋并叠加在其表面的陨石坑的大小-频率分布（SFD）表明，早于VB侵位的地形的绝对模式年龄近似为3.7Ga。(2)在乌托邦平原的西南部分，缺乏部分被VB材料包围的陨石坑，这意味着VB的就位速度快于撞击陨石坑的积累速度，并且与VB由于流出通道的水灾难性释放而就位的地质短时间一致（例如，卡尔，M.H. [19961年。火星上的水牛津大学出版社，纽约，第229页）。(3)叠加在VB表面上的陨石坑的SFD表明其绝对模式年龄为3.6-3.5 Ga。代表VB地层上限的蚀变流的绝对模式年龄估计为3.5Ga。(4)大多数较大的（即，大于1公里）的撞击坑显示出喷出物的形态（壁垒状和煎饼状喷出物），这表明目标物质中存在冰/水。煎饼状喷出物的远端部分严重降解（不是由于海湾）。这表明这些陨石坑形成于含有较高挥发物丰度的目标中。(5)两个撞击坑的直径范围都有重叠（从大约2公里到大约60公里）。火山口与煎饼状喷出物集中在中央部分的乌托邦盆地（不到类似的1000公里，从盆地中心）和壁垒火山口发生在周边的盆地。这种陨石坑的空间分布模式表明，乌托邦平原中心的物质含有更多的冰/水。(6)乌托邦平原中央部分周围的蚀刻流是从VB表面之下喷发出来的。然而，它们的形态和退化模式与熔岩不一致，而是表明由于泥火山作用而形成的流动。(7)蚀刻流在空间上与巨大的多边形，有证据表明，这些功能填充的乌托邦平原的中心部分之前，它被覆盖的Elysium衍生单位。多边形槽和蚀刻流的区域的外（南部）边缘大致对应于从煎饼状喷出物到城墙喷出物的过渡。这表明多边形和流动区域的外边缘可能勾勒出大片水/冰（直径约2000公里）的较深部分，这些水/冰可能存在于西方晚期的乌托邦平原中心。(C)2013 Elsevier Inc. All rights reserved.
Results of our detailed geological mapping and interpretation of the nature and relative and absolute model ages of units and structures in the SW portion of Utopia Planitia (20-45 degrees N, 100-120 degrees E) suggest the following. (I) The size-frequency distribution (SFD) of craters that both are buried by materials of the Vastitas Borealis units (VB) and superpose its surface indicate that the absolute model ages of terrain predating the emplacement of the VB is similar to 3.7 Ga. (2) Lack of craters that are partly embayed by materials of the VB in the SW portion of Utopia Planitia implies that the emplacement of the VB was faster than the rate of accumulation of impact craters and is consistent with the geologically short time of emplacement of the VB due to catastrophic release of water from outflow channels (e.g., Carr, M.H. [19961. Water on Mars. Oxford University Press, New York, p. 229). (3) The SFD of craters that superpose the surface of the VB indicates an absolute model age of similar to 3.6-3.5 Ga. The absolute model ages of etched flows, which represent the upper stratigraphic limit of the VB, are estimated to be similar to 3.5 Ga. (4) The majority of the larger (i.e., >1 km) impact craters show ejecta morphologies (rampart and pancake-like ejecta) that are indicative of the presence of ice/water in the target materials. The distal portions of the pancake-like ejecta are heavily degraded (not due to embayment). This suggests that these craters formed in targets that contained higher abundances of volatiles. (5) The diameter ranges of the craters with either rampartor pancake-like ejecta are overlapping (from similar to 2 to similar to 60 km). Craters with pancake-like ejecta are concentrated within the central portion of the Utopia basin (less than similar to 1000 km from the basin center) and rampart craters occur at the periphery of the basin. This pattern of the crater spatial distribution suggests that materials within the center of Utopia Planitia contained more ice/water. (6) Etched flows around the central portion of Utopia Planitia were erupted from beneath of the surface of the VB. Their morphology and pattern of degradation, however, are inconsistent with lava and, instead, indicate formation of the flows due to mud volcanism. (7) Etched flows are spatially associated with giant polygons and there is evidence that these features populated the center portion of Utopia Planitia before it was covered by the Elysium-derived units. The outer (southern) edge of the zone of polygonal troughs and etched flows approximately corresponds to the transition from pancake-like ejecta to rampart ejecta. This suggest that the outer edge of the zone of the polygons and flows may outline the deeper portions of the large body (similar to 2000 km across) of water/ice that likely existed in the center of Utopia Planitia in late Hesperian. (C) 2013 Elsevier Inc. All rights reserved.