Granites built by sheeting in a fault stepover (the Sanabria Massifs, Variscan Orogen, NW Spain) |
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| Authors: | N Vegas A Aranguren & J M Tubía |
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| Institution: | Departamento de Geodinámica, Facultad de Ciencias, Universidad del País Vasco, a.p. 644, E-48080 Bilbao, Spain |
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| Abstract: | The Sanabria region (Central Iberian Zone, Variscan belt of Spain) shows an asymmetric thermal dome marked by migmatites accompanied by the Ribadelago and the Sotillo plutons. These small plutons display pronounced mineralogical variations. Biotite granodiorites and tonalites prevail, and granites and gabbros are common. Both plutons are confined in the releasing stepover of a transpressional shear zone that strikes 120°E and dips 70°SW. Most of the igneous rocks form sheets parallel to the shear zone. Magnetic foliations and lineations in the igneous rocks are parallel, respectively, to the shear bands and stretching lineations observed in the shear zone. The formation of these igneous sheets at high angle to the main axis of the regional field stress is explained by a combination of the fault-valve behaviour of the shear zone with the power of melt overpressure to open and ascend through previously formed planar structures, like S- or C-planes. |
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