Contrasting mechanism of crustal growth: Geodynamic evolution of the Paleoproterozoic granite–greenstone belts of French Guiana
The Paleoproterozoic granite–greenstone belts of French Guiana formed during a period of major crustal growth at the scale of the Earth. Two contrasting mechanisms of crustal growth have been identified by recent structural, metamorphic, geochronological and geochemical investigations in the Cayenne...
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| Published in: | Precambrian research 1998-10, Vol.92 (2), p.165-193 |
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| Main Authors: | , , , , , , |
| Format: | Article |
| Language: | eng |
| Subjects: | |
| Online Access: | Get full text |
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| Summary: | The Paleoproterozoic granite–greenstone belts of French Guiana formed during a period of major crustal growth at the scale of the Earth. Two contrasting mechanisms of crustal growth have been identified by recent structural, metamorphic, geochronological and geochemical investigations in the Cayenne–Régina region, which is part of the northern granite–greenstone belt of French Guiana. Following the formation of oceanic crust, which is characterized by a tholeiitic volcanic sequence dated at 2174±7
Ma, the early stage of crustal generation was marked by successive building of calc-alkaline plutonic–volcanic complexes, with the formation of the Ile de Cayenne complex dated at 2144±6
Ma to the north, and of the Central Guiana complex dated at 2115±7
Ma to the south. This first period of crustal generation by accumulation of mantle-derived magmas was followed by a period of crustal recycling and tectonic accretion. Sediments derived from the granite–greenstone belts were deposited in large marginal basins, such as the Orapu basin, separating the plutonic–volcanic complexes. Convergence between the newly formed crustal blocks caused deformation during the Transamazonian orogeny of the Orapu marginal basin caught in between the Ile de Cayenne and Central Guiana complexes. Oblique convergence is further characterized by the development of en-echelon pull-apart basins along the North Guiana Trough sinistral strike-slip shear zones, affecting the edges of the Orapu marginal basin. The lithological succession in these basins is typical of foreland basins, and the metamorphic and structural evolution of the Kaw and Régina basins in the Cayenne–Régina region indicate burial to depth up to 20
km in a context of heterogeneous transpression. The geochemical signature of small syntectonic granitic plutons dated at 2093±8
Ma and 2083±8
Ma emplaced along the major strike-slip shear zones is consistent with crustal thickening and partial melting of an enriched crustal source. These features suggest that the last stage of the Transamazonian orogeny was marked by oblique convergence, collision and crustal thickening in a similar way to modern orogens. |
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| ISSN: | 0301-9268 1872-7433 |