Global correlations of mid-ocean-ridge basalt chemistry with seismic tomographic images

Abstract

THERMAL convection in the mantle is the most important dynamic process in the Earth's interior. Two quite different approaches are currently used to provide and analyse information regarding lateral temperature variations in the upper mantle. On the one hand, the major-element chemistry of basalts erupted at mid-ocean ridges is directly influenced by the temperature of the mantle beneath1–5; on the other, seismic velocity studies6–17 can be used to map lateral temperature variations on a global scale (lower seismic velocities corresponding to higher mantle temperatures). Here we make a first attempt at relating these two approaches, by examining the global co-variation between mid-ocean-ridge basalt chemistry and upper-mantle shear-wave velocity. We find a strong correlation between basalt chemistry and variations in seismic velocity at depths of 100–170 km and lateral scale-lengths of 1,000–2,400 km, supporting a common thermal origin for the two types of signal. The departure of a few points from the general correlation may either reflect locally poor resolution of the tomographic model or, more interestingly, point to real anomalies that will repay closer examination.