Formation, erosion and exposure of Early Amazonian dikes, dike swarms and possible subglacial eruptions in the Elysium Rise/Utopia Basin Region, Mars

Hundreds of narrow, linear ridge segments are found in the transition zone between the Elysium Rise and the Utopia basin, occurring as both single and multiple ridges. The ridges are distinctive because of their very linear, steep-sided nature, their often sharp ridge crest (which sometimes is fractured), their association with stubby flows, their continuity over long distances and their cross-cutting of different terrain. The linear ridges are interpreted to be single dikes and dike swarms, either emplaced as normal dikes or as dikes emplaced subglacially feeding an explosive or effusive eruption. Five dike swarms are identified, having lengths ranging from 10–45 km and being between 1–7 km wide, while single ridges are up to 20 km long and 100–500 m wide. In the areas of dike swarms, crustal dilatation is estimated to vary from 15–60%. Dikes emplaced en echelon suggest that variations in the local stress field caused rotation during dike emplacement and dikes crosscutting flow units imply that dike emplacement can account for some of the observed linear fractures in the area. The ridges both modify and constrain Early Amazonian flows and flood plain deposits suggesting intense dike emplacement in the Early Amazonian. The association with different stages of inverted craters, as well as some features of ice-related origin (possible ice-cauldron and tindar-like features), indicate that the dikes may have been exposed due to eolian erosion and loss of volatile rich units subsequent to their emplacement.