[Previous] | [Session 38] | [Next]
B. R. Tufts, R. Greenberg, G. Hoppa, P. E. Geissler (Lunar and Planetary Lab, University of Arizona)
Lithospheric displacement features consistent with the presence of a subsurface liquid layer at the time of the displacements, continue to be imaged by Galileo. Lateral motion features on recent images include bands near Moytura Regio, Tyre, and in regional maps centered at 40N, 229W, and 15N, 76W. A band NE of Tyre exhibits more than 30 km of dilation and left-lateral shear, making it comparable to large south polar gray bands. Class 2 (dilational) ridges in the Greenberg et al [1] classification system appear in many locations. Bands and dilational ridges may be variations on the theme of tidal cracking and "working," with the differences due to availability of lateral room and changes in tidal stress. The distribution of bands and ridges suggests that lateral motion is global and long-lived, consistent with [2, 3]. Within bands, the corners of the medial cracks seem to be rounded off with successive infilling [4]. One interpretation is that these corners were melted by a relatively warm infill material. Blocks bordering bands in the C3 wedges region show little or no cracking parallel to and adjacent to the bands, unlike the Uruk Sulcus region of Ganymede [5], suggesting that the subsurface decoupling layer allowing their motion was a low-friction one, e.g. liquid water. Also, more examples of possible ridge-induced plate flexure have been found, evidenced by flanking cracks and shading indicative of collateral depressions. Examples include ridges near Tyre and ridges antipodal to the possible flexure near Conamara Chaos, where flexural parameters suggest a thin lithosphere [2]. Flexural parameters are not yet known for these newly-seen ridges. [1] Greenberg et al., Icarus, 1997. Sub. [2] Tufts et al. LPSC 29 1998. [3] Pappalardo and Sullivan, Icarus, 1996. 123: p. 557-567. [4] Sullivan et al., Nature, 1998. 391: p. 371-373. [5] Head et al., 1997, LPSC 28.