FRACTURE-ZONES IN THE NORTH-ATLANTIC FROM COMBINED GEOSAT AND SEASAT DATA

We present a new tectonic fabric map of the northern and central North Atlantic Ocean floor from 10-degrees-S to 66-degrees-N based on combined Geosat and Seasat altimetry data. Short wavelength vertical gravity along-track was derived by Hilbert transforming and high-pass filtering Geosat and Seasat deflection of the vertical profiles. The along-track gravity data were used in conjunction with magnetic anomaly data to locate a large number of fracture zones as well as extinct spreading ridges and V-shaped structures. We traced many fracture zones more continuously and closer to adjacent continental margins than was previously possible. We also mapped a number of unnamed fracture zones and fracture zone segments, many of which were previously uncharted. We have evaluated the agreement between the mapped fracture zones and synthetic flow lines as predicted from recent plate models for the opening of the North, central North and South Atlantic. Most fracture zones in this area correlate quite well with synthetic flow lines, supporting the proposition that Geosat/Seasat altimetry data serve as a useful tool to map fracture zones, where insufficient bathymetric data are available. Many fracture zones, including some small-offset fracture zones in the central North Atlantic, have been stable and follow tectonic flow lines for tens of millions of years. However, many other fracture zones do not reflect a "railroad track" pattern of plate motions. The geometry of many small- and medium-offset fracture zones indicates that the ridge axis discontinuities that produce them can migrate along the ridge, causing off-axis traces that deviate from tectonic flow lines. Velocity-space diagrams constructed using a recent relative and absolute present day plate motion model indicate that some low-angle V-shaped troughs and ridges are likely formed by migration of the plate boundary relative to a mesospheric reference frame. Other low-angle V-shaped structures reflect slow migrations/oscillations of small-offset ridge axis discontinuities that are distinct from both tectonic flow lines and V-shapes reflecting "absolute" plate motions. High-angle V-shaped structures are the result of fast migrating ridge axis discontinuities (propagating rifts).