MID-ATLANTIC RIDGE VOLCANISM FROM DEEP-TOWED SIDE-SCAN SONAR IMAGES, 25-DEGREES-29-DEGREES-N

We present deep-towed side-scan sonar mosaics of the inner valley floo r of eight spreading segments at the slow-spreading Mid-Atlantic Ridge between 25 degrees and 29 degrees N. An analysis of these images, whi ch well-resolve features a few tens of meters in size, confirms that t he multitude of small seamounts, with diameters between 0.5 and 3 km i dentified on the inner valley floor from previously collected multibea m bathymetry data, are volcanically constructed. Moreover, these image s reveal that these volcanoes have distinct surface morphologies not e vident in the coarser resolution multibeam bathymetry maps: 83% of the seamounts have a hummocky (bulbous) morphology; the other 17% have a smooth morphology. In addition to near-circular seamounts, small (1-2 km long) volcanic ridges are abundant in our study regions, and are no t, in general, seen in the bathymetry maps. We combine these new morph ological data with existing models for the construction of the shallow oceanic crust to obtain a better understanding of the melt delivery s ystem that builds the distinctive seafloor topography at the slow-spre ading Mid-Atlantic Ridge.