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The basic tectonic features of the western Mediterranean are explained by a model invoking the activity of a toroidal convection cell in the upper mantle, uncoupled from the base of the lithosphere (a situation different from the usual plate tectonic conditions). The key feature of this model is that the current is visualized as eroding the base of the lithosphere in a manner analogous to the erosion of sand by running water or wind, producing a pattern of inverted subcrustal ripples concentric about the rising mantle column. Isostatic subsidence of zones thinned in this manner would have given rise to the geosynclinal furrows which were present throughout most of the Mesozoic and the Tertiary. Continued removal of lithosphere beneath such a furrow would eventually bring it to the point where it would no longer be capable of resisting compressive stresses applied by the thick zone behind it, which would be pressing outward as a result of the drag of the mantle current. At this point the furrow would be crushed between the two adjacent thick zones, and its sedimentary fill would be bulldozed out and slide away as great gravity nappes. Subcrustal erosion and the episodic outward movements as furrows collapsed would lead to the removal of continental crust from above the rising mantle column. When convection ceased, new oceanic crust in the central area would subside to its normal isostatic level, while the surrounding regions would rise in compensation, producing the pattern seen today.

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