Timing of oceans on Mars from shoreline deformation
Timing of oceans on Mars from shoreline deformation
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DOI：
10.1038/nature26144
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发表时间：
2018-03-29
期刊：
影响因子：
64.8
通讯作者：
Hemingway, Douglas J.
中科院分区：
文献类型：
--
作者：
Citron, Robert I.;Manga, Michael;Hemingway, Douglas J.
广泛的证据表明存在着古代火星海洋（1-8）。最引人注目的是北方平原上假定的古代海岸线（2，7）。然而，这些海岸线没有遵循等位面，这被用来挑战它们通过早期海洋形成的概念，因此质疑这样一个海洋的存在。海岸线与恒定海拔的偏离可以用塔尔西斯形成后发生的真正的极地漂移来解释（10），塔尔西斯是一个火山区，主导着火星的重力和地形。然而，来自海洋的表面负荷只有在塔尔西斯形成于远离赤道的地方才能驱动极地漂移（10），大多数证据表明塔尔西斯形成于赤道附近（11-15），这意味着目前没有解释海岸线偏离与我们对火星的地球物理理解一致的等位线。在这里，我们表明，在海岸线地形的变化可以解释由塔尔西斯的侵位所造成的变形。我们发现，海岸线一定是在塔尔西斯就位之前和期间形成的，而不是像以前假设的那样是在之后形成的。我们的研究结果表明，火星上的海洋形成得很早，与山谷网络同时存在，并指出火星上海洋的演变与塔尔西斯火山活动的开始和衰落之间存在密切关系，对早期火星的地质，水文循环和气候具有广泛的影响。
Widespread evidence points to the existence of an ancient Martian ocean(1-8). Most compelling are the putative ancient shorelines in the northern plains(2,7). However, these shorelines fail to follow an equipotential surface, and this has been used to challenge the notion that they formed via an early ocean(9) and hence to question the existence of such an ocean. The shorelines' deviation from a constant elevation can be explained by true polar wander occurring after the formation of Tharsis(10), a volcanic province that dominates the gravity and topography of Mars. However, surface loading from the oceans can drive polar wander only if Tharsis formed far from the equator(10), and most evidence indicates that Tharsis formed near the equator(11-15), meaning that there is no current explanation for the shorelines' deviation from an equipotential that is consistent with our geophysical understanding of Mars. Here we show that variations in shoreline topography can be explained by deformation caused by the emplacement of Tharsis. We find that the shorelines must have formed before and during the emplacement of Tharsis, instead of afterwards, as previously assumed. Our results imply that oceans on Mars formed early, concurrent with the valley networks(15), and point to a close relationship between the evolution of oceans on Mars and the initiation and decline of Tharsis volcanism, with broad implications for the geology, hydrological cycle and climate of early Mars.