Marshall, S.T., Kattenhorn, S.A. (2005)

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A revised model for cycloid growth mechanics on Europa: Evidence from surface morphologies and geometries


Icarus 177: 341-366.

Although a single model currently exists to explain the development of curved Europan cycloids, there have been no systematic studies of the range of morphologies and quantifiable geometric parameters of cycloidal features. We address variations in geometry along individual cycloid segments, characterizing differences in cusp styles and angles, and addressing the morphologic aspects of cycloid segments and cusps. In so doing, we illustrate how geometric and morphologic evidence imply a formation mechanism that differs from the existing model in several aspects. The current model states that cycloids are initiated as tensile fractures that grow in a curved path in response to rotating diurnal tidal stresses on Europa. However, the geometry of a cycloid cusp necessitates that shear stress was resolved onto the existing cycloid segment by the rotating diurnal stresses at the instant of cusp formation. Furthermore, we observe that cycloid cusps have a strikingly similar geometry to tailcracks that developed at the tips of many ridge-like strike-slip faults on Europa in response to shearing at the fault tip. We suggest that this similarity in geometries can be attributed to an identical formation mechanism whereby cycloid cusps form by a tailcracking process. We therefore present a revised, mechanically-based model for cycloid formation that retains the basic premise that crack growth is governed by diurnal stresses, but describes the development of cycloid cusps in response to resolved shear stresses at the tips of existing cycloid segments. The ratio of normal to shear stress at the time of tailcrack formation dictates the cusp angle and, over longer time periods, influences the morphologic evolution of the cycloid segment as it is repeatedly reworked by tidal stresses.

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Citations:


This paper has been cited in the following 15 works:


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Kattenhorn, S.A., Hurford, T.A. 2009. Tectonics of Europa. In: Pappalardo, R.T., McKinnon, W.B., Khurana, K., eds, Europa. University of Arizona Press, 199-236.

Nimmo, F., Manga, M. 2009. Geodynamics of Europa's icy shell. In: Pappalardo, R.T., McKinnon, W.B., Khurana, K., eds, Europa. University of Arizona Press, 381-404.

Groenleer, J.M., Kattenhorn, S.A. 2008. Cycloid crack sequences on Europa: Relationship to stress history and constraints on growth mechanics based on cusp angles. ICARUS 193 (1): 158-181.

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Kattenhorn, S.A., Billings, S.E., Groenleer, J.M., Marshall, S.T., Vetter, J.C. 2006. Fracture access through the Europan ice shell: Geologic constraints for the selection of an optimal surface entry site. PROCEEDINGS OF THE EUROPA FOCUS GROUP WORKSHOP 5, NASA Ames Research Center, Moffett Field, California, Feb. 27-28, 2006: 63-64.

Kattenhorn, S.A., Marshall, S.T. 2006. Fault-induced perturbed stress fields and associated tensile and compressive deformation at fault tips in the ice shell of Europa: implications for fault mechanics. JOURNAL OF STRUCTURAL GEOLOGY 28 (12): 2204-2221.

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Nimmo, F., Prockter, L., Schenk, P. 2005. Europa's icy shell: Past and present state, and future exploration. ICARUS 177 (2): 293-296.


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