Paleomagnetism of Basalts and Interlayered Sediments Drilled during DSDP Leg 49 (N–S Transect of the Northern Mid-Atlantic Ridge)

Abstract

We report paleomagnetic results for Leg 49 obtained onboard Glomar Challenger and subsequently in the shore laboratories. The intensity of remanent magnetization of basaltic ocean crust fluctuates with depth at all sites; within-site variation of this property exceeds between-site variation. No significant differences in the remanence intensity of the upper ocean crust occur between magnetic anomalies 13 and 2' or between groups of sites at latitudes 37°N, 45°N, and 63°N. An arithmetic mean intensity of 5.0 × 10~3 emu/cm 3 for all Leg 49 basalt specimens is close to previous average values for samples from the North Atlantic Ocean floor. Median destructive fields, weak field susceptibilities, and Königsberger ratios are comparable with previous results from ocean floor basalts. The Königsberger ratios show that remanence dominates the magnetization of the upper ocean crust. In seven out of eight holes, the sign of the stable inclination is appropriate to the magnetic anomaly. Values of stable inclination fluctuate with depth. At two sites, abrupt changes in stable inclination together with other paleomagnetic properties make it easy to define distinct magnetic units. At the other sites, it is more difficult to locate boundaries using magnetic evidence alone. Fewer magnetic units than petrographic units are identified in all cases.

Paleomagnetism and Some Magnetic Properties of Basalts from the Bermuda Triangle

“…Although Lowrie (1977) noted that the paleoinclinations of basalts from early DSDP sites are consistent with the paleolatitudes of the sites (correlation coefficient = 0.912), the results of many studies show that the stable inclinations are often anomalous (usually shallow) relative to those expected from a geocentric axial dipole field (Cox and Doell, 1962;Brooke et al, 1970;Lowrie andOpdyke, 1972, 1973;Ade-Hall et al, 1973;and Ryall and Hall, 1977). Sometimes reversals are observed in the vertical column of a single hole (e.g., Faller et al, 1979 and. Furthermore, the relatively low intensities of remanent magnetization (JNRM) which are usually observed imply that a magnetic layer several kilometers thick is required to produce the observed anomalies (Lowrie, 1973;Scientific Party, 1975;and Harrison, 1976).…”

Paleomagnetism of Middle Jurassic Basalts, Deep Sea Drilling Project Leg 76

“…This study Taylor et al, 1973Marshall, 1978Bleil and Smith, 1980Hall and Ryall, 1977Johnson, 1979Johnson, 1979Faller et al, 1979Faller et al, 1979Faller et al, 1979Faller et al, 1979Faller et al, 1979 Reference This study Taylor et al, 1973Marshall, 1978Levi, 1980Levi, 1980Bleil and Petersen, 1977Johnson, 1979Johnson, 1979Faller et al, 1979Faller et al, 1979Faller et al, 1979Faller et al, 1979Faller et al, 1979 …”

A Magnetic Study of the Oceanic Crust in the Vicinity of Sites 482, 483, and 485, Leg 65

“…Figure 7 shows the variation of magnetic intensity with age for rocks from the Mid-Atlantic Ridge and for the dredged samples studied here. These values have been compiled from a number of sources, and include samples obtained from dredging and submersible sampling near the Mid-Atlantic Ridge axis (Johnson and Atwater, 1977) and by drilling during DSDP Legs 37 (Ryall et al, 1977), 45 , and 49 (Faller et al, 1979). The ages are determined from magnetic anomalies.…”