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[1] We utilize imaging data from the Galileo spacecraft to investigate band formation on one of Jupiter's moons, Europa. Bands are polygonal features first observed in Voyager data close to Europa's anti-Jovian point and represent areas where preexisting terrain has been pulled apart, allowing new material to move up into the gap. We examine the detailed morphology of several bands imaged at different resolutions and lighting geometries. We identify several distinct morphological characteristics, including central troughs, hummocky textures, and ridge and trough terrains, some of which are common among the bands studied. In many cases, bands have initiated along segments of one or more preexisting double ridges, ubiquitous within Europa's ridged plains. Distinctive morphological features and high standing topography imply that the bands formed from compositionally or thermally buoyant ice, rather than liquid water. Comparisons between Europan band morphologies and features found on terrestrial mid-ocean ridges reveal several similarities, including axial troughs, subcircular hummocks, normal faults, and indications of symmetrical spreading. We conclude that terrestrial mid-ocean ridge rifting is a good analogy for Europan band formation. If a terrestrial seafloor-spreading model is applicable to Europan bands, we speculate that band morphologies might be related to the relative rate of spreading of each band. Bands may have contributed significantly to the resurfacing of Europa. Europan bands we examine predate (but do not postdate) lenticulae and related features, implying that the style of resurfacing on Europa has changed over recent geological time in these regions.

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[1] We have used high-resolution scanned air photos and field measurements to analyze fracture population systematics for the Reykjanes fissure swarm in order to determine the effect of rift obliquity on the evolution of fracture populations on the Reykjanes Peninsula, SW Iceland. The peninsula is oriented approximately 30°oblique to the direction of plate motion. Data show significant differences between the strike, length, and degree of development of fractures along the margin of the fissure swarm and those in the center of the zone of active volcanism. Along the margin, fractures are long, highly segmented extension fractures, and normal faults with offset on the order of several meters and a predominant strike 20°oblique to the trend of the plate boundary (rift axis). In the center of the zone of active volcanism, fractures are generally shorter, straighter, fewer in number, and strike approximately perpendicular to the direction of maximum horizontal extension and parallel to the trend of eruptive fissures. Right-lateral oblique-slip faults striking approximately perpendicular to the spreading direction are present in the center of the rift zone. Scaled experimental models of oblique extension predict a significant change in fracture strike at the rift margins due to the presence of a secondary stress field; on the Reykjanes Peninsula, this corresponds to the boundary between thicker and thinner brittle crust. The models confirm that right-lateral oblique-or strike-slip faults accommodate significant left-lateral shear where deformation is distributed in a rift zone.