Labyrinth Terrain on Titan

The Cassini/Huygens mission revealed a terrain type on Saturn's moon Titan of dissected, elevated plateaux with a high density of valleys named labyrinth terrain. We define four subtypes of labyrinth terrains: valleyed, polygonal, finely-dissected, and the possible outlier Kronin Labyrinth. We mapped the locations of all labyrinths imaged by Cassini and found they are distributed preferentially at high latitudes. We characterize the labyrinths by morphometric parameters such as intervalley width, valley width, and percent valleys. We find many labyrinths contain closed valleys, which constrains their formation and evolution. We also examine their low microwave emissivity spectral characteristics and find that the labyrinths are consistent with a bulk composition of dominantly organic materials, with some component of water ice – characteristics similar to Titan's undifferentiated plains. Our analyses show that labyrinths are ancient terrains – only the mountains and hummocky terrains are older. This implies that significant organic production occurred early in Titan's history. The organic inventory represented by the labyrinths is estimated to be 15–42% of the solid organic inventory of Titan (or 14–35% of the total surface organics, if the hydrocarbons of the lakes and seas are also included). Our preferred formation of the labyrinth terrains is erosion through dissolution and fluvial processes that dissect the plateau in a manner similar to dissolution geology (karst) on Earth. This scenario requires that the organics that make up the labyrinth terrain be soluble in methane and/or ethane liquids. It also suggests that the origin of the plateaux may have derived from Titan's past chemical production and subsequent depositional record.

卡西尼-惠更斯（Cassini/Huygens）任务在土星卫星土卫六（Titan）上发现了一类被命名为迷宫地形（labyrinth terrain）的地貌类型，其特征为被深切的抬升高原且谷地密度极高。我们将迷宫地形划分为四种亚型：谷地型、多边形型、精细深切型，以及可能的异常类克罗恩迷宫（Kronin Labyrinth）。我们对卡西尼探测器成像获取的全部迷宫地形的位置进行了地质填图，发现它们优先分布于高纬度区域。我们采用形态计量参数（包括谷间距、谷地宽度及谷地占比）对迷宫地形开展了系统的特征刻画。研究发现多数迷宫地形包含封闭谷地，这一发现对其形成与演化机制构成了约束条件。我们还分析了其低微波发射率的光谱特性，结果表明迷宫地形的主体以有机质为主，且含有一定占比的水冰组分——这一特征与土卫六上未分异平原的特征高度相似。我们的分析显示，迷宫地形属于古老地貌——仅山地与丘状地形的年代更为久远。这意味着在土卫六的早期演化阶段，曾发生过大规模的有机质生成过程。由迷宫地形所代表的有机质储量估计约占土卫六固态有机质总储量的15%~42%；若将湖泊与海洋中的烃类物质纳入统计，则约占地表总有机质的14%~35%。我们更支持的迷宫地形形成机制为：通过溶解作用与河流侵蚀作用对高原进行深切改造，该过程与地球上的喀斯特（karst）溶解地质作用相似。该模型要求构成迷宫地形的有机质可溶于甲烷和/或乙烷液体，同时也暗示这类高原的起源可能源自土卫六过往的化学生成过程与后续的沉积记录。