Morphology and Crustal Structure of the Kane Fracture Zone Transverse Ridge

The Kane Fracture Zone (KFZ) Transverse Ridge is an anomalously shallow ridge which parallels the KFZ for over 200 kilometers east of its intersection with the Mid-Atlantic Ridge rift valley. Sea Beam bathymetry and gravity data have been used to determine the morphology and density structure of the ridge, and travel-time data from two seismic refraction experiments have been used to constrain its seismic velocity structure. The transverse ridge first appears on older lithosphere opposite the eastern ridge-transform intersection (RTI). It rises to a maximum height of about 2000 m above the bordering KFZ trough 40 km east of the intersection area. Although bathymetry data along the western limb of the KFZ are relatively sparse, a ridge of similar dimensions appears to b e absent. The KFZ transverse ridge has a decidedly flexural shape in cross-section with a high, steep, south-facing wall and a gently sloping northern side. The grain of the ridge-parallel topography north of the KFZ continues undisrupted across the transverse ridge suggesting that the ridge has formed by vertical uplift of this crust. Seismic ray tracing and gravity analyses indicate that the KFZ transverse ridge is not locally compensated by an overthickened crust, but is underlain by crustal thicknesses and velocities similar to that of normal oceanic crust on either side of the KFZ. Anomalously thin crust is present only immediately beneath the KFZ trough and the south-facing wall of the transverse ridge. These constraints, and the existence of the transverse ridge on the older plate, preclude several previously proposed models for its origin including flexural bending due to differential subsidence across the fracture zone, constructional volcanism and serpentine diapirism. Although no other single mechanism provides a completely satisfactory explanation for the origin of the KFZ transverse ridge, the most likely mechanism appears to be a combination of thermal and viscodynamic forces operating near the RTI