Patthoff, D.A., Kattenhorn, S.A. (2010)


The relationship between fracture sets and the South-Polar Terrain dichotomy on Enceladus

Eos, Transactions of the American Geophysical Union 91, Fall Meeting Supplement, Abstract P33A-1557.

Young fractured ice in the south-polar terrain (SPT) of Enceladus is separated from older regions of the moon by a narrow (9-50 km) band of deformation that defines a morphological dichotomy. The dichotomy is 100s of meters higher than the SPT and is divided into segments, some of which appear to be parallel fold-like structures and others that are dominated by numerous fractures. Overall, the trend of the dichotomy is semi-parallel to lines of latitude and has a shape that is roughly rectangular with the longer sides made of segments of the fold-like features. The parallel trend of some of the folds with the present day tiger stripes may be attributed to contraction to either side of the dilational tiger stripes. However, how the dichotomy has evolved, especially the older parts, and how the segments relate to the older fractures within the SPT remains unexplored. Our previous work has revealed an age sequence of fracture sets with similar properties to the tiger stripes. These fractures appear to have been rotated (clockwise, CW) about the south pole relative their original locations, which we attribute to long-term nonsynchronous rotation of a decoupled ice shell. The older sets include prominent fractures that are longer and wider than other fractures in each set and stand out as potentially ancient versions of the named tiger stripes. We have identified 7 potential paleo-tiger stripes that have a range of ages and orientations. The youngest of the paleo-tiger stripes are rotated ~28° CW relative to the orientation of the present day tiger stripes, the next oldest are rotated an additional ~47° CW, and the oldest another ~78° CW. If these paleo-tiger stripes were similar in form and function to the contemporary tiger stripes, localizing crustal spreading in the past, they should also have influenced the SPT dichotomy analogously to the present day tiger stripes. Accordingly, if the tiger stripes are responsible for fold belt-like features in the SPT dichotomy, the paleo-tiger stripes may have contributed to the creation of older fold belts in the dichotomy. These older fold belts should share similar ages and orientations to the fracture sets with which they are associated and may also have been modified as the ice shell rotated across a tidally-locked stress state. Our mapping shows that the youngest of the paleo-tiger stripes share a similar orientation to the fold belts of the dichotomy between longitudes of ~290° and 330° and near 90°. Additional correlations of the fold belts to older fracture sets likely exist. Other sections of the dichotomy are dominated by fractures instead of folds. The fractured terrains are centered near longitudes of 0° and 220° and spread out ~25° longitude. The fractures are not randomly oriented but instead appear to have systematic sets, some of which correlate to the orientations of the paleo-tiger stripes. In order to establish a correlation with the paleo-tiger stripes we: 1) identify what specific structures comprise the dichotomy, 2) determine if different parts of the boundary have different ages by examining crosscutting relationships, 3) determine if sections of the dichotomy are genetically related to the fracture sets in the SPT, and 4) explore how the fracture sets interact with and influence the dichotomy.

External link: AGU database



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