Abstract: The behaviour of the lithosphere under extensional strain is different whether the surface of the lithosphere is above or below the level that would be reached by the asthenosphere in its absence. Below this level, the continuity of the old lithosphere may be rapidly broken and oceanic accretion starts. Above this level, extensive thinning of the old lithosphère occurs until the level is reached, and then the asthenospheric material may break out to the surface. The thinning probably depends on the strain rate. Two extreme cases must be distinguished. For low strain rates: the lower lithosphere may be thinned by diapiric intrusions and lithospheric sinking; the upper one is much less affected, as occurs in the African Rifts or the Rhine Graben. For high strain rates, the whole lithosphère is thinned rather uniformly, as occurs in the Aegean region and probably on many continental margins. The greatest portion of the lithosphere is extended plastically, while the upper brittle portion, about 10 km thick, is extended by normal faulting. The pattern of faulting in these widely extended areas is compared to a pack of cards resting at an angle on a plane, with each card (tilted block) making a slight angle with the preceding one. Using this simple model, we discuss the case of the Pindos basin of the Hellenides. Similar intra-continental basins 150 to 400 km wide may be created before the subsidence increases sufficiently for oceanic accretion to begin. We point out that these basins are especially susceptible to compressional failure whenever the stress system changes from extensional to compressional. Consequently, many orogens are localized along such zones of earlier extension, as shown by geological studies of the Western Alpine system.
Publication Year: 1982
Publication Date: 1982-01-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 77
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