Gravitational sliding on the Mid-Atlantic Ridge at the Kane Transform:Implications for submarine basin-slope degradation and deformation

摘要

Deep-tow side-scan sonar imagery,along with submersible and camera surveys,provides a synoptic view of the sea-floor geology,leading to critical observations and new interpretations for previously unknown gravitational sliding features on the Mid-Atlantic Ridge at the Kane Transform (23 deg 38 min N).The sliding on the rift-valley wall occurred mostly as massive slumps of slope-forming gabbroic bed rocks,possibly along mechanically weak,low-angle (approx 30 deg) detachment faults,creating frontal cuspate ridges and downslope-trending lineaments.The sliding on the transform-valley wall occurred mostly as debris avalanches,producing distributed surficial sediment and bedrock clasts in an apron of hum-mocky and chaotic terrain on the lower slope,steeply dipping (approx 70 deg) amphitheaterlike escarpments on the upper slope,and downslope-trending ridges and lineaments on the middle slope.Local and global comparative analysis suggests that distinct geologic settings of submarine slopes exert fundamental influence on the nature,style,and scale of gravitational sliding.The rift-valley wall differs from the transform-valley wall primarily because of their different structural grain,lithological complexity,and sediment thickness.The steeply dipping (approx 25 deg),sediment-free rift-valley wall on the Mid-Atlantic Ridge contrasts strongly with the gently dipping (approx 5 deg),passive continental margins loaded with thousands of meters of petroliferous sedimentary rocks.Results from comparative analysis not only add to the knowledge of complexities of submarine gravitational sliding structures but also contribute to a better understanding of the differences in sea-floor degradation and deformation processes in contrasting submarine geologic settings represented by mid-ocean ridges and passive continental margins.