ABSTRACT
This chapter looks at the most distinctive belts of high heat flow, ocean ridges and rift valleys, to examine the evidence that indicates how the features form and develop. Basalt flows are associated with the East African rift valley, and closer to home they can also be found in northern Ireland and western Scotland. The basalt plateaux of Antrim and the Inner Hebrides are of comparable age with that rifting episode. The central rift is obviously broken up into sections and offset by some kind of fault orthogonal to the central ridge. Earlier rift valleys disappear as lateral spreading occurs, pushing the rift slopes away to form subordinate parallel ridges, which become more and more degraded away from the crest and eventually form the floor of the oceanic abyssal plains. The emphasis upon the importance of upwarping along the rift system makes it very tempting to draw a direct parallel with the processes at work beneath an ocean ridge.
