A two-day meeting of the Tectonic Studies Group was held in London at the Geological Society on 3-4 October 1991, to consider relationships between continental extension, super continent break-up, magmatism and mantle plumes. The approach was multidisciplinary, with contributions from geophysists, geochemists and tectonic geologists. There were 28 talks and 11 poster presentations, with about 150 people attending.
The conference was opened by convenor B. C. Storey (British Antarctic Survey, Cambridge) followed by a session on relevant geophysical and geochemical principles. D. L. Anderson (California Institute of Technology) gave a stimulating keynote lecture on mantle reservoirs and seismic tomographic evidence for mantle circulation. He suggested that the source of all 'enriched' basalts such as ocean island basalt (OIB) and continental flood basalt was in a shallow mantle layer relative to the source of depleted mid-ocean ridge basalt (MORB). He presented new, high resolution global seismic tomography data, and argued from these that deep-rooted hot mantle up-wellings underlie mid-ocean ridges and back arc basins, but that mantle plumes, as narrow jets underlying hot spots cannot be oberved by seismic means, nor are required by geochemical data. M. A. Menzies (Royal Holloway and Bedford New College) reviewed the penological, age and thickness variations in continental lithospheric mantle, and its suitability as a mantle source for continental basalts. He described reaction zones and metasomatic fronts generated by intrusion of magmas into mantle rock, and argued that such processes generate a range of mantle compositions like those of source regions of continental flood basalts.