Abstract

The thickness of the lithosphere and melt generation are controlled by the temperature of the mantle, which in turn is dominated by convective heat transfer. Traditional geological and geophysical arguments provide limited, but strong, local constraints on mantle temperature, from thermal models of spreading ridges and sinking slabs, and from the mineralogy of garnet peridotite nodules brought up by alkaline magmas. The widespread installation of broad band seismometers now allows the S wave structure of the mantle to be mapped in considerable detail using surface waves to a depth of _{300 km. Vs is principally controlled by temperature, not by composition, so we now have a method of mapping the 3D temperature of the upper part of the mantle. I will discuss our most recent maps, produced from Keith Priestley’s model of Vs generated from about three million seismograms. The maps show a number of unexpected features. They show that the planform of the convective circulation beneath Africa and the Middle East is a 3D spoke pattern, with the hubs corresponding to the proposed locations of plumes. Beneath Asia thick lithosphere (}250 km) is now being generated by continental shortening beneath the Zagros, Hidu Kush, Pamirs, Tien Shan and Tibet.