Frozen Martian lahars? Evaluation of morphology, degradation and geologic development in the Utopia-Elysium transition zone

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• 作者：G.B.M. Pedersen
• 关键词：Mars ; Ice&ndash ; volcano interactions ; Lahars ; Elysium Volcanic province ; Galaxias
• 刊名：Planetary and Space Science
• 出版年：2013
• 出版时间：1 September, 2013
• 年：2013
• 卷：85
• 期：Complete
• 页码：59-77
• 全文大小：21086 K

文摘

Regional coverage of high-resolution data from the CTX camera has permitted new, detailed morphologic analysis of the enigmatic Utopia-Elysium flows which dominate the transition zone between Elysium volcanic province and Utopia Planitia. Based on topographic and morphologic analysis of the Galaxias region, this study supports the lahar hypothesis put forth by previous works and suggests that the center and the margins of the outflow deposits have very diverse morphologies that can be explained by varying degrees of water drainage and freezing. Regular channel and flood plain deposits are found in the central part of the outflow deposits, whereas the marginal deposits are interpreted to contain significant amount of ice because of their distinct morphological properties (smooth, lobate flow-fronts with upward convex snouts, unusual crater morphologies, raised rim fractures and localized flow fronts indicating rheomorphism). Thus, this study suggest that, unlike terrestrial lahars, lahar emplacement under Martian conditions only drain in the central parts, whereas the water in the margins of the outflow deposit (¡«75 % of the total outflow deposit in the Galaxias region) freezes up resulting in a double-layered deposit consisting of ice-rich core with an ice-poor surface layer.

It is here furthermore suggested that continued intrusive volcanic activity was highly affected by the presence of the ice-rich lahar deposits, generating ground-ice-volcano interactions resulting in a secondary suite of morphologies. These morphologies include seventeen ridges that are interpreted to be m?berg ridges (due to their NW-SE orientation, distinct ridge-crests and association with fractures and linear ridges) and depressions with nested faults interpreted to be similar to terrestrial ice-cauldrons, which form by enhanced subglacial geothermal activity including subglacial volcanic eruptions. These sub-lahar intrusions caused significant volatile loss in the ice-rich core of the distal lahar deposit and resulted in remobilization, deflation, and retreat of the lahar deposits, explaining the raised rim fractures, enclosed depressions, and small isolated islands found in distal lahar deposits.