Kane Fracture Zone

Abstract

Abstract. The Kane Fracture Zone probably is better covered by geophysical survey data, acquired both by design and incidentally, than any other fracture zone in the North Atlantic Ocean. We have used this data to map the basement morphology of the fracture zone and the adjacent crust for nearly 5700 km, from near Cape Hatteras to the middle of the Mesozoic magnetic anomalies west of Cap Blanc, northwest Africa. We use the trends of the Kane transform valley and its inactive fracture valley to determine the record of plate-motion changes, and we interpret the basement structural data to examine how the Kane transform evolved in response to changes in plate motion. Prior to about 133 Ma the Kane was a small-offset transform and its fracture valley is structurally expressed only as a shallow ( <0.5 kin) trough. In younger crust, the offset may have increased to as much as 190 km (present offset 150 km) and the fracture valley typically is up to 1.2 km deep. This part of the fracture valley records significant changes in direction of relative plate motion (5~ ~ near 102 Ma, 92 Ma, 59 Ma, 22 Ma, and 17 Ma. Each change corresponds to a major reorganization of plate boundaries in areas around the Atlantic, and the fracture-zone orientation appears to be a sensitive recorder of these events.The Kane transform has exhibited characteristic responses to changes in relative plate motion. Counterclockwise plate-motion changes put the left-lateral transform offset into extension, and the response was for ridge tips at the ridge-transform intersections to propagate across the transform valley and against the truncating lithosphere. Heating of this lithosphere appears to have produced uplift and formation of a well developed transverse ridge that bounds the inactive fracture valley on its older side. The propagating ridge tips also rotated toward the transform fault in response to the local stress field, forming prominent hooked ridges that now extend into or across the inactive fracture valley. Clockwise (compressional) changes in relative plate motion produced none of these features, and the resulting fracture valleys typically have a wide-V shape.The Kane transform experienced severe adaptions to the changes in relative plate motion at about 102 Ma (compressional shift) and 92 Ma (extensional shift), and new transform faults were formed in crust outside the contemporary transform valley. Subsequently, the transform offset has been smaller and the rates of change in plate motion have been more gradual, so transformfault adjustment has been contained within the transform valley. The fracture-valley structure formed during extensional and compressional changes in relative plate motion can be decidedly asymmetrical in conjugate limbs of the fracture zone. This asymmetry appears to be related to the 'absolute' motion of the plate boundary with respect to the asthenosphere.

Ridge segmentation, tectonic evolution and rheology of slow-spreading oceanic crust

“…at 22-24 Ma [Tucholke et al, 1996], which was also recorded by the Kane FZ [Tucholke and Schouten, 1988]. We thus remap the data by rotating crust younger than 20 Ma by 10°t owards the west, and crust older than 20 Ma by 190 to account for the change in plate motion.…”

“…At that time the overall trend of the ridge axis was similar to that at present. However, the spreading direction was rotated -200 counterclockwise, as recorded by the traces of the Kane [Tucholke and Schouten, 1988] and Atlantis FZs (Figure ib), resulting in a more oblique ridge configuration. The gravity anomalies over the crust generated during this period show more pronounced gravity lineations and higher RMS than near the axis (Figures lb and 2), suggesting better organized segmentation.…”

Seismic and magnetic constraints on the structure of upper oceanic crust at fast and slow spreading ridges

“…This pattern, however, places the pole of opening for the Atlantic in an unrealistic position, namely, a few hundred kilometers to the south, and is more likely an indicator of temporal variability in spreading rate. Calculations extending past anomaly 5 show the average spreading rate in this area to be constant for the past 10 Myr [Tucholke and Schouten, 1988]. Although earlier bathymetric data show little evidence for propagating rifts [Sempere et al, 1993], high-resolution data,collected aboard the Japanese support vessel Yokosuka in 1994, resolve the off-axis scars of several southward propagating rifts N.…”

“…Sea surface magnetic anomaly identification has determined that the ridge immediately north of the Kane transform has been spreading asymmetrically at an average half rate near 14 mm/yr to the west and 13 mm/yr to the east for the past 10 Myr [Klitgord and Schouten, 1986;Tucholke and Schouten, 1988]. Several studies have previously been conducted along the western Kane transform and adjacent rift valley.…”

The evolution of lithospheric deformation and crustal structure from continental margins to oceanic spreading centers

“…The segmented magnetic high running parallel to the margin is the East Coast Magnetic Anomaly (ECMA). Solid gray lines show the location of the Kane and Northern fracture zones as mapped by Tucholke and Schouten (1988) on the basis of a combination of basement structure and magnetic data. White lines ilustrate the location of the offset zone traces identified in this study.…”