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Continental Rift Basins |
Dept of Earth Sciences, The University, Parks Road, Oxford OX1 3PR, UK
Rifts are one of the most spectacular features of global morphology. Within oceans they separate plates as new oceanic crust is created. Within continents they may form deep valleys such as the Rhine graben, within which runs one of the world’s busiest waterways. They are often floored by deep lakes, such as Lake Baikal, the deepest lake in the world today whose floor lies 1700 m below the surface of the lake. Ancient rifts are the sites of petroleum accumulations beneath the margins of the Atlantic, in the North Sea and in China, of coals and oil shales and of minerals, including phosphates, barite, Cu-Pb-Zn sul-phides and uranium (Robbins 1983). Of all the world’s rifts none can match in scale and diversity the Great Rift System, which runs for over 7000 km and includes the East African Rift System and its extension through the Red Sea into the Dead Sea, to form a unique feature of global geology. Its study is important not only for what it can tell about the nature and origin of present-day rifts, the thermal, magmatic and tectonic processes which gave rise to them, climatic changes, and sedimentary, particularly lacustrine and volcaniclastic, processes. It is also essential for the understanding of the processes which formed passive continental margins, all of which are underlain by rifted sedimentary basins, and failed rifts whether they formed within continents or at the junction of continents and oceans.
Early workers on rifts were impressed by the wide valleys, 40–50 km across, filled by young
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