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473651 
Journal Article 
Syntectonic crustal melting and high-grade metamorphism in a transpressional regime, Variscan Massif Central, France 
Gebelin, A; Roger, F; Brunel, M 
2009 
1 
Tectonophysics
ISSN: 0040-1951 
477 
3-4 
229-243 
English 
Hot collisional orogens are characterized by abundant syn-kinematic granitic magmatism that profoundly affects their tectono-thermal evolutions. Voluminous granitic magmas, emplaced between 360 and 270 Ma, played a visibly important role in the evolution of the Variscan Orogen. In the Limousin region (western Massif Central, France), syntectonic granite plutons are spatially associated with major strike-slip shear zones that merge to the northwest with the South Armorican Shear Zone. This region allowed us to assess the role of magmatism in a hot transpressional orogen. Microstructural data and U/Pb zircon and monazite ages from a mylonitic leucogranite indicate synkinematic emplacement in a dextral transpressional shear zone at 313 +/- 4 Ma. Leucogranites are coeval with cordierite-bearing migmatitic gneisses and vertical lenses of leucosome in strike-slip shear zones. We interpret U/Pb monazite ages of 315 +/- 4 Ma for the gneisses and 316 +/- 2 Ma for the leucosomes as the minimum age of high-grade metamorphism and migmatization respectively. These data suggest a spatial and temporal relationship between transpression, crustal melting, rapid exhumation and magma ascent, and cooling of high-grade metamorphic rocks. Some granites emplaced in the strike-slip shear zone are bounded at their roof by low dip normal faults that strike N-S, perpendicular to the E-W trend of the belt. The abundant crustal magmatism provided a low-viscosity zone that enhanced Variscan orogenic collapse during continued transpression, inducing the development of normal faults in the transpression zone and thrust faults at the front of the collapsed orogen. (C) 2009 Elsevier B.V. All rights reserved. 
Crustal melting; High-grade metamorphism; Transpression; U/Pb dating; Variscan French Massif Central; lower continental-crust; u-pb systematics; shear zone; montagne noire; granitic complex; saint-sylvestre; axial zone; extensional tectonics; ductile deformation; plateau daigurande