Fine-scale isotopic heterogeneity in the sub-Atlantic mantle

Sup(87/86)Sr and sup(143/144)Nd studies are reported, on a series of basaltic glass samples from the mid-Atlantic ridge intersection with the Kane Fracture Zone located at 220-240N, which have implications for the dynamics of mantle melt segregation and the role of a major transform in mantle convection. The results indicate the existence of isotopic heterogeneities in oceanic basalt glasses from adjacent sites which implies that large scale magma chambers and regions of melt segregation do not exist in the upper mantle below the Kane Fracture Zone. (U.K.)