A Synthesis of Marine Geological/Geophysical Data for Ocean Crustal Drilling on Mid-Atlantic Ridge: ABSTRACT

Abstract

We have recently completed a synthesis of all available marine geological/geophysical data in the Mid-Atlantic Ridge area of the central Atlantic Ocean. The synthesis was undertaken to evaluate future scientific drill sites. The final product is a set of maps on Mercator projection for the following areas: Area VIII-1, 33° to 38°N, 30° to 44°W; Area VIII-2, 28° to 33°N, 34° to 48°W; Area VIII-3, 22° to 28°N, 39° to 50°W. For each area the data synthesized includes: contours of bathymetry at a 500-m (1,640-ft) contour interval, contours of free-air gravity at a 10 mgal contour interval, total intensity magnetic anomaly profiles and identifications along ships' tracks, locations and thicknesses of sediment ponds fr m seismic reflection data, seismic crustal structure from sonobuoy and other refraction measurements, surface sediment core locations, sediment types and ages, locations of available rock dredges, heat flow measurements, seismicity and regional tectonics. In addition, detailed maps showing near bottom observations at the Mid-Atlantic Ridge in the vicinity of the Kane Fracture Zone (24°N), TAG area (26°N), Oceanographer transform (35°N), and the Famous Area (37°N) are included. The segmental nature of the Mid-Atlantic Ridge crest is clearly shown. It is interpreted as a succession of relatively short spreading centers separated and offset by, in general, small offset transform zones. The average spacing between the transform zones is less than 50 km (31 mi) and rather uniform. The fracture zones may be traced away from the ridge transform section, but not necessarily as a continuous bathymetric feature. The gravity anomalies present a smoothed (low-pass filtered) version of the bathymetry. In some places (e.g., the eastern extension of fracture zone B at 36.5°N), the gravity anomalies display the continuation of fracture zones where the bathymetry does not. The magnetic anomaly identifications show the variable behavior of the North Atlantic accreting boundary through time. Consistent asymmetric spreading is found south of the Kane Fracture Zone (24°N), indicating continuous eastward migration of the accreting boundary. Variable asymmetric spreading is documented farther to the north. We find that the asymmetry is preserved in the individual magnetic anomalies, suggesting that the emplacement of the magnetic source has occurred in a relatively narrow zone. Further, we believe that the extreme variability of magnetic anomaly shapes in the North Atlantic may be caused by variable asymmetric behavior of the individual spreading centers. End_of_Article - Last_Page 538------------