Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p21b1601s&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P21B-1601
Physics
[5475] Planetary Sciences: Solid Surface Planets / Tectonics, [6222] Planetary Sciences: Solar System Objects / Ganymede, [8010] Structural Geology / Fractures And Faults, [8149] Tectonophysics / Planetary Tectonics
Scientific paper
Grooved terrain on Ganymede consists of parallel to sub-parallel ridges and troughs at a variety of spatial scales. Grooved terrain is observed in imagery as individual lanes and polygonal crosscutting swaths of bright terrain. Grooved terrain has been interpreted as the product of crustal extension expressed as rotational block faulting. Individual polygons show internally consistent groove morphology, size, and orientation. These similarities may indicate that the groove system within that polygon developed within a uniformly oriented extensional strain field. Extension magnitudes interpreted for groove sets range from a few percent to fifty percent. Differentiation of Ganymede’s interior, tidal distortion, and nonsynchronous rotation have been postulated as driving mechanisms for crustal extension on Ganymede. Differentiation is interpreted to result in a bulk volume increase accommodated by distributed extension of the lithosphere. Tidal distortion, the repeated dynamic cycling of stress conditions that vary with orbital and rotational position, can subject portions of the lithosphere to repeated transitions between extension and contraction. Nonsynchronous rotation can modify the frequency and amplitude of tidal distortion, including superposing secondary and even tertiary distortion cycles. We propose tectonic inversion, the reactivation of extensional faults as reverse faults, as a candidate process for the accommodation of crustal contraction on Ganymede. In the case of tidal stress cycling extensional faults can form at stress magnitudes that are not sufficient to induce reverse faulting. Once formed, fault planes can be reactivated as reverse faults at lower stress magnitudes than are required to form reverse faults. We use physical analogue models to test the reactivation of normal faults as a mechanism to accommodate contraction. Model results suggest that reverse displacement can be accommodated by fault systems initiated under extension. Model fault systems subjected to cyclic displacement reversals of equal magnitude can result in a fault system with a net extensional strain. Model fault patterns compare favorably with faults interpreted from imagery of grooved terrain on Ganymede. Slip tendency, the ratio of maximum shear stress to normal stress acting on a surface, is sensitive to surface orientation and the form of the stress tensor. Slip tendency analysis of model fault systems compares favorably with mapped fault patterns and interpreted stress fields on Ganymede, indicating that cyclic stress fields are a viable mechanism to accommodate contraction of Ganymede’s lithosphere.
Morris Alan P.
Sims Darrell W.
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