The structure and paleomagnetism of North Atlantic Ocean layer 2: segregation vesicle determinations ( DSDP).

Segregation vesicles contain solidified residual melt. The segregation vesicle technique of seafloor basalt orientation is based on the assumptions that: 1) the orientation of this residue is mainly gravity controlled and forms a geopetal feature, and 2) rocks remain relatively stationary during the time of segregation, solidification, and magnetization. By application of this technique it is possible to determine the horizontal cooling of certain seafloor basalts recovered in drill cores and then correct the magnetic direction for the dip of the rocks, determine the true thickness of lithologic units (measured perpendicular to the dip), and estimate the dip direction, with some degree of confidence. This technique was applied to DSDP holes 332A, 332B, 334, 395, 395A, and 396B, which penetrated 117 to 583m into basaltic basement crust of the N Atlantic Ocean. The deformation of the upper 500m of oceanic basement documented here implies that either marine magnetic lineations may not always record the Earth's magnetic field at the time that portion of crust formed or are evidence for a deeper magnetic source layer in the N Atlantic.-from Author