Evolution of central massifs |
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| Abstract: | In spite of the abundance of definitions of central massifs, there is no integration of data Khain and Sheynmann (1960) define the central massifs as a residual province of older cycles within a progressive folding system. They note such provinces tend to be remodeled by the younger movements, yet retain their basic “setup” while exerting influence on the surrounding rocks. Central massifs may be classified into: 1) blocks of ancient Precambrian platforms, 2) blocks of Paleozoic or Mesozoic folded structures within younger geosynclinal system and 3) provinces of early consolidation which serve as “growth centers” within a geosynclinal system. Despite the differences in origin and age of central massifs, they have many common features. All are within geosynclinal belts and serve to divide them into segments; they are polygonal to diamond-shaped and are bounded by deep rifts with “flows” of ultrabasic to basic magma. As a rule, there are three periods of development of a massif with a single tectonic cycle: 1) continental regimen with denudation 2) minor marine trangression, block deformations, volcanism and granite intrusion and 3) transition to intermontane low with associated volcanic activity. Central massifs show,a mosaic of variously trending faults caused largely by vertical movements. Some students attribute the much thinner crust within the central massifs, based on geophysical studies, to a redistribution of deep-seated substance from the massif toward the geosyncline. — W. D. Lowry. |
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