Geometry and Kinematics of Structures in the South Polar Terrain of Enceladus: Over-Interpreting Kinematics?

Details Geometry and Kinematics of Structures in the South Polar Terrain of Enceladus: Over-Interpreting Kinematics? Geometry and Kinematics of Structures in the South Polar Terrain of Enceladus: Over-Interpreting Kinematics?

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p11b1598g&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P11B-1598

Other

[5475] Planetary Sciences: Solid Surface Planets / Tectonics, [6055] Planetary Sciences: Comets And Small Bodies / Surfaces

Scientific paper

There remains some debate as to whether fractures, ridges, grooves and other structures in the SPT region of Enceladus are the result of tidally-driven extensional, contractional or a combination of dip-slip and strike slip deformation. We document fractures, faults, and ridges that are both kinematically compatible and incompatible with current models for strain fields in the SPT. We utilize traditional geometric and kinematic structural analysis to map structures within the SPT. These observations may then be used to constrain models for the evolving strain field within the SPT. Six linear fractures, > 120 km in length, define the structural morphology of the SPT. These include the 'tiger stripes' as well as two elongate fractures that occur to the north of Damascus Sulcus and are subparallel to each other. These two fractures are associated with smaller pinnate fractures striking at 45° from the tiger stripes, or parallel to the tidal axis or the direction of maximum stress. These feather fractures are consistent with a component of right-lateral strike slip motion. Elsewhere, the tips of the recognized 'tiger stripes' display an apparent dextral curvature with radii of approximately 5-10 km. Such curved fractures are best observed at the tips of Alexandria Sulcus. In contrast, at the tips of Baghdad and Damascus Sulcii, both arcuate and linear fractures systems appear to emanate from the tips. The Mohr-Coulomb criterion for shear fracture predicts that faults develop with angles around 45° to the maximum compressive stress. The fact that the series of 'tiger stripes' are at an orientation of approximately 45° from 0° longitude, the direction of maximum stress, suggests that there is a component of shear force acting on Enceladus' SPT. The presence of ridge-like structures with amplitudes ranging from 10's to 1000 m located in regions between the tiger stripes is consistent with local contraction. While the type of folding mechanism is not known, minor longitudinal fractures along the crests of some ridges is consistent with a buckling model. It has been suggested that the tiger stripes are under varying compression and tension forces at different times in relation to each other. It is possible that the ridge-groove structures between the 'tiger stripes' formed by contraction of the ice terrains between sub-parallel, extending 'tiger stripes'. Linear fractures 10's of kms long, orthogonal to the 'tiger stripes', have been variously interpreted as transform faults, similar to those found on Earth. However, cross cutting relations, differences in geomorphology, and a lack of reliably identified 3-D displaced markers make such interpretations tenuous. Based on observations and analysis, we propose that the dominant strain field recorded in the features of the SPT is the result of transcurrent shearing and extension. However, the magnitude and direction of strains cannot be quantified until adequate 3-D topographic data are obtained and analyzed. Given the complexity of kinematic and geometrical relations in the SPT, we urge caution in interpreting displacement fields from structural orientation in the SPT.

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