Morphology and tectonics of the Kane Transform from Sea Beam bathymetry data

Abstract

High‐resolution Sea Beam data have been used to construct an accurate, regional scale, bathymetric map of the Kane Transform, a large‐offset, slowly slipping (30 mm/yr), central North Atlantic transform. The Kane Transform trends about 100°, nearly orthogonal to the regional trend of the adjacent Mid‐Atlantic Ridge (MAR) rift valley. The transform valley walls are composed of an alternating series of ridges and troughs which parallel the regional trend of the MAR. The ridges narrow and deepen toward the transform valley over distances of 10–20, km, and the intervening troughs widen into distinct closed‐contour depressions that appear to be relict nodal basins. The morphologic elements found on either side of the transform valley exhibit along‐strike continuity and represent undisrupted displacement markers. The swath of terrain sandwiched between these markers is only several kilometers wide and is made up of elongate basins, and ridges that integrate to create a distinctive transform‐parallel grain. This interval, the transform tectonized zone (TTZ), marks the time‐averaged location of strike‐slip tectonism as parcels of crust move from each intersection along the transform interface. The TTZ is widest (∼6 km) near the eastern ridge‐transform intersection (RTI) and narrows to a strand less than 3 km wide along the central and western portions of the transform. Along the eastern portion of the transform valley a narrow (∼3 km) median ridge several hundred meters high can be traced for more than 40 km along the valley floor, and a similar, but shorter, feature is also present near the western RTI. At both RTIs the neovolcanic zone from the adjacent rift valley can be traced, as a series of constructional edifices, across the entire intersection area to the Opposing transform valley wall. At the eastern RTI the neovolcanic zone wraps around the eastern edge of the nodal basin, while at the western RTI it appears to bisect a paired nodal basin located in the intersection area. A line drawn connecting the ends of each neovolcanic zone lies within the narrow TTZ and has a strike of 098°. Using the bathymetric map of the Kane Transform as a record of the time‐integrated tectonic evolution of this large, slowly slipping ridge‐transform‐ridge plate boundary, we have constructed a simple model for the evolution of RTIs. Our model emphasizes the interplay between temporal variations in crustal production rates (i.e., variations in the volume of basaltic melt production) along oceanic spreading centers and extensional tectonism. This model can explain the existence of nodal basins at RTIs and relict nodal basins along transforms and fracture zones, as well as the occurrence of regularly spaced ridge and trough topography on the ridge flanks.