Abstract The erosion rates and mechanisms operating on Mount Sharp in Gale crater, Mars were assessed via experiments performed by the SAM instrument to determine the cosmogenic noble gas contents of Murray mudstone formation samples Mojave 2 and Quela. Previous measurements of samples from the Aeolis Palus depression between Mount Sharp and the north rim of Gale crater indicate that scarp retreat-generated surfaces formed within the last 100 Ma. In contrast, Mojave 2 yielded exposure ages of 1,320±240 (3He), 910±420 (21Ne), and 310±60 Ma (36Ar). Quela gave a 3He age of 1,460±200 Ma; 21Ne and 36Ar from this sample could not be quantified due to isobaric interferences. The discordant and young 36Ar exposure age in Mojave 2 is likely the result of interaction with water which dissolved the chlorine-bearing host phases of this nuclide. The most probable exposure scenario is that both Mojave 2 and Quela have been at the surface for the most recent ∼1 Ga after the overlying few meters of rock were removed in a geologically rapid exhumation episode. Based on local geomorphology, scarp retreat is the most likely mechanism for the exposure at these two sites. The exposure ages measured throughout Curiosity's traverse indicate that the net removal of rock has proceeded more recently on Aeolis Palus than on the lower slopes of Mount Sharp. The implied differential erosion rate is insufficient to explain how Mount Sharp formed, even over billions of years. Instead, given that the surfaces on Mount Sharp have existed for >1 Ga, the mountain must have formed early, likely during the Hesperian. This study provides direct quantitative support for inferences based on crater counts that Mount Sharp had eroded to close to its current form before onset of the Amazonian.

中文翻译：

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盖尔陨石坑（火星）中的十亿年暴露年龄表明夏普山形成于亚马逊时期之前

摘要 通过SAM仪器进行的实验评估了火星盖尔陨石坑夏普山的侵蚀速率和作用机制，以确定莫里泥岩地层样品莫哈韦2和奎拉的宇宙惰性气体含量。先前对夏普山和盖尔陨石坑北缘之间的 Aeolis Palus 洼地样本的测量表明，在过去的 100 Ma 内形成了陡峭的后退产生的表面。相比之下，莫哈韦沙漠 2 的暴露年龄为 1,320±240 (3He)、910±420 (21Ne) 和 310±60 Ma (36Ar)。Quela给出的3He年龄为1,460±200 Ma；由于同量异位素干扰，无法定量该样品中的 21Ne 和 36Ar。Mojave 2 中不一致且年轻的 36Ar 暴露年龄可能是与水相互作用的结果，水溶解了该核素的含氯宿主相。最可能的暴露情况是，在地质学上的快速剥脱事件中，覆盖的几米厚的岩石被移除后，莫哈韦 2 号和奎拉最近都在地表约 1 Ga。根据当地地貌，陡峭的撤退是这两个地点最可能的暴露机制。好奇号在整个穿越过程中测量的暴露年龄表明，与夏普山较低的斜坡相比，Aeolis Palus 上的岩石净移除进行得更晚。隐含的差异侵蚀率不足以解释夏普山是如何形成的，即使是在数十亿年的时间里。相反，考虑到夏普山上的地表已经存在超过 1 Ga，这座山一定很早就形成了，很可能是在 Hesperian 时期。