Morphology and crustal structure of the Kane Fracture Zone Transverse Ridge

Abstract

The Kane Fracture Zone (KFZ) transverse ridge is an anomalously shallow ridge which parallels the KFZ for over 200 km 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 modeled to constrain its seismic velocity structure. The transverse ridge first appears on older lithosphere opposite the eastern ridge‐transform intersection. 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 is not present. 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 only present immediately beneath the KFZ trough and along the south facing wall of the transverse ridge., These constraints, and the formation of the KFZ 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 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 ridge‐transform intersection.