Volcanism and structure of continental rift valleys

Abstract

T he common image invoked by the term “riff” is of extensive linear depressions embellished by the constructional features of recent volcanic activity. It is to the credit of Drs Pinkerton and Macdonald, both of Lancaster University, that they interpreted "rift" in an imaginative way and organized a group of speakers who, although falling under the general generic heading of “rifters”, dealt with the subject over a long time scale and wide spatial distribution. Drs Williams and Banks were conventional enough in that their subjects were respectively the geology and geophysics of the East African rift system in Kenya. Professor King summarized the geology in and around the non-volcanic Baikal rift. Dr Upton presented the fascinating story of the intense faulting and associated magmatism of the late Precambrian Gardar province of South Greenland whereas Dr Howell Francis injected new data and enthusiasm into the magmatic history of the Midland Valley of Scotland. Professor Bailey, painting on a wider canvas, considered the causes of African rifting and magmatism. Dr Williams, dealing with the distribution, composition and age of the Cenozoic volcanics both within and away from the Kenya rift, emphasised the growing complexity of the story as more data become available. Lavas that at one time had been considered to belong to the same phase, had been shown to differ in both composition and age. There was no simple compositional progression in either space or time, this lack of obvious correlation applied also between volcanic structures and those in the underlying