CRUSTAL EVOLUTION OF ENCELADUS' SOUTHERN, LEADING, AND TRAILING HEMISPHERES

Based on interpretations of crustal features on Enceladus, we developed a global kinematic map of the satellite and suggest a series of events that define its crustal evolution. Features associated with Enceladus’ South Polar Terrane (SPT) are indicative of diapirism based on interpretations and kinematic analysis of structures similar to those observed overlying terrestrial salt diapirs. Based on observations of previously modeled diapir evolution and cross-cutting relationships of features on Enceladus, we propose an order of structure formation leading to the current configuration found in the southern hemisphere.

At the SPT, extensional fracturing of four parallel features termed ‘tiger stripes’, coupled with tidal heating in the icy crust, resulted in passive diapirism as relatively warm and therefore less dense ice ascended to the surface. As diapirism became active, uplift of the crust overlying the crest occurred creating a surrounding area of contraction in response to a central region of extension and the flow of ice down slope. Radial extensional fault zones initiated over the crest and continued to lengthen away from the SPT, producing grabens. Features comparable to ogives, found in terrestrial valley glaciers, developed as overlying ice flowed into these grabens. The initiation of a less prominent contractional belt located to the north in the trailing hemisphere occurred by foreland thrusting due to ongoing contractional forces from the SPT.

Structures in the equatorial regions of Enceladus’ leading and trailing hemispheres suggest that similar but older events occurred in these locations. The orientation of ridges and grooves and characteristics of features, including structures analogous to ice rises on earth, also suggest rotational displacement of crustal blocks over time in the southern, trailing, and leading hemispheres. Features analogous to terrestrial pressure ridges indicate that localized patches of subsurface water were once present in the equatorial region of the trailing hemisphere, possibly during a paleo diapir event. To further support these interpretations, hypsometry data as well as calculations of ice creep in environments of low gravity and temperature should be analyzed.