The three large volcanoes in the Tharsis region of Mars: Arsia, Pavonis, and Ascraeus Montes all have fan-shaped deposits (FSDs) on their northern or western flanks consisting of a combination of parallel ridges, knobby/hummocky terrain, and a smooth, viscous flow-like unit. The FSDs are hypothesized to have formed in the Amazonian during a period of high spin-axis obliquity which redistributed polar ice to the equatorial Tharsis region resulting in thick (> 2 km), flowing ice deposits. Based on previous ice flow simulations and crater surveys, the ridges are interpreted to be recessional drop moraines formed as debris on the ice sheet surface was transported to the ice margin—forming a long ridge sequence over an extended (∼100 Myr) period of ice sheet retreat. We test this hypothesis using a high-resolution, thermomechanical ice sheet model assuming a lower ice loss rate (~ 0.5 mm/year) than prior work based on new experimental results of ice sublimation below a protective debris layer. Our ice flow simulation results, when combined with topographic observations from a long sequence of ridges located interior of the Pavonis FSD, show that the ridged units were more likely deposited during one or more periods of glacial advance (instead of retreat) when repetitive pulses (approx. 120 kyr periodicity) of ice accumulation during high obliquity produced kinematic waves which advected a large volume of surface debris to the ice margin. If ridge deposition does occur during glacial advance, it could explain the cyclic pattern of ridge spacing and would link the dominant, 120 kyr periodicity in obliquity to the time interval between adjacent ridges. By measuring the spacing between these ridges and applying this timescale, we constrain the velocity of glacial margin to be between 0.2 and 4 cm/Earth year—in close agreement with the numerical simulation. This re-interpretation of the FSD ridged unit suggests that the timescale of FSD formation (and perhaps the duration of the Amazonian high obliquity period) was shorter than previously reported.

中文翻译：

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火星Pavonis Mons的冷基冰川作用：冰期前冰m沉积的证据。

火星塔里西斯地区的三座大型火山：亚西亚，帕沃尼斯和阿斯格里乌斯·蒙特斯，在其北侧或西侧均具有扇形沉积物（FSD），包括平行的山脊，knob形/丘陵地带以及光滑，粘性流状单元。据推测，FSD是在自旋轴倾角较高的时期形成于亚马逊河中的，该时期将极地冰重新分布到赤道塔西斯地区，形成了厚厚的（> 2 km）流动冰层。根据先前的冰流模拟和陨石坑勘测，将山脊解释为凹陷的滴流，因为冰原表面上的碎屑被运送到冰缘，形成了较长的山脊序列（〜100 Myr）片材撤退。我们使用高分辨率来检验这个假设，热机械冰盖模型基于保护性碎片层以下冰升华的新实验结果，假设其冰损失率（〜0.5 mm /年）比以前的工作低。我们的冰流模拟结果，与从Pavonis FSD内部的一系列长脊的地形观测结果相结合，表明当重复脉冲（在高倾角时，冰积聚的周期大约为120年）产生了运动波，该运动波将大量的表面碎屑平移到了冰缘。如果在冰川发展过程中确实发生了山脊沉积，则可以解释山脊间距的周期性模式，并将倾斜的主要120 kyr周期性与相邻山脊之间的时间间隔联系起来。通过测量这些山脊之间的间距并应用该时间尺度，我们将冰川边缘的速度限制在0.2至4 cm /地球年之间，这与数值模拟非常吻合。对FSD脊状单元的这种重新解释表明，FSD形成的时间尺度（也许是亚马逊高倾角时期的持续时间）比以前报道的要短。