SEGMENTED LINEAMENTS AS PALEOSTRESS INDICATORS OF GLOBAL STRESSES ON EUROPA (Invited Presentation)

Europa’s is extensively fractured by linear structures of length scales from 100s of meters to >1000 km. The formation and evolution of these features has been variously attributed to globally imposed surface stresses caused by diurnal tides, nonsynchronous rotation, and/or polar wander. Previous studies conducted, on both regional and local scales, to evaluate stress mechanisms responsible for the formation of linear features have used the locations and orientations of prominent lineaments on Europa as constraints. These studies have generally relied on an a priori assumption of the initial stress state that led to the formation of a given lineament (i.e., tension, compression, strike-slip motion). Results have varied significantly, with evidence presented for nonsynchonous rotation of as little as 25° [1] to as much as 1000° [2] and/or polar wander of 30° [3] or 80° [4] about Europa’s tidal axis. This suggests that, to better understand the stress history of Europa’s surface, models of global stress mechanisms need additional constraints.

Recent work has described several prominent lineaments on Europa that are segmented [5]. In terrestrial research, geometries associated with the segmentation of fractures or fracture systems have been well studied using theory, experiments, and field work. That research has provided a basic framework for assessing local and remote stress environments associated with their formation and has demonstrated that the process is an intrinsic property of brittle materials [e.g., 6]. [5] showed that the segmented lineaments on Europa were analogous to segmented fractures on Earth and used that relationship to describe the remote stress orientations and relative magnitudes that would have been necessary to allow their formation. This a priori knowledge of the stress state involved in the formation or evolution of these prominent lineaments provides a key additional constraint for assessing models of global stress.

References: [1] McEwen, A.S. (1986), Nature 321, 49-51; [2] Sarid et al. (2005), Icarus, 172, 469-479; [3] Sarid et al. (2002), Icarus 158, 24-41; [4] Schenk et al. (2008), Nature 453, 368-371; [5] Patterson and Head (2010), Icarus 205, 528-539; [6] Olson and Pollard (1989), Geology 17, 345-348.