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Comptes Rendus Géoscience
Volume 340, n° 4
pages 223-232 (avril 2008)
Doi : 10.1016/j.crte.2007.12.006
Received : 28 June 2007 ;  accepted : 10 December 2007
U–Pb Shrimp-RG zircon ages of Variscan igneous rocks from the Guilleries massif (NE Iberia pre-Mesozoic basement). Geological implications
Datations U–Pb par la méthode Shrimp sur zircons de roches ignées varisques du massif des Guilleries (socle pré-Mésozoïque du Nord-Est de l’Espagne). Implications géologiques

Francisco José Martínez a, , Joan Reche a, Alexander Iriondo b, c
a Departament de Geologia, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain 
b Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, C.P. 76230 Juriquilla, Querétaro, Mexico 
c Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado 80309, USA 

Corresponding author.

One diorite sheet, syntectonic with the dominant D2 foliation in the Guilleries massif, 50km south of the Variscan Pyrenean axial zone, has provided an U–Pb age of 323.6±2.8Ma, one of the oldest in that part of the Variscan basement. This age seems to be the same as that of the sillimanite-grade syn-D2 metamorphism in the deepest part of the massif; it is clearly separated from that obtained in three syn-extensional D3 leucogranite veins (305.3±1.9; 301.5±1.7; 299.0±2.3Ma) and the coeval biotite granites (305.9±1.5Ma). The leucogranites are 20Ma younger than the syn-D2 diorite and the sillimanite-grade metamorphism. They are considered the melting-induced products in the host rocks, at a deeper level than that of the present outcropping of the mantle-related biotite granites during the extensional collapse (D3) of the chain in the Lower Stephanian.

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La datation U–Pb d’une intrusion laminaire dioritique syntectonique de la foliation dominante D2 (qu’elle soit d’origine compressive ou extensive), dans le massif des Guilleries, situé 50km au sud de la zone axiale varisque pyrénéenne, indique un âge de cristallisation de 323,6±2,8Ma, un des plus anciens obtenu dans cette région du socle varisque. Cet âge doit correspondre à l’âge du métamorphisme à sillimanite syn-D2 dans les parties profondes du massif ; il est nettement distinct des âges obtenus sur trois veines de leucogranite syn-extension D3 (305,3±1,9 ; 301,5±1,7 ; 299,0±2,3Ma) et un granite à biotite contemporain (305,9±1,5Ma). Ces leucogranites postdatent de 20Ma la diorite syn-D2 et le métamorphisme à sillimanite. Ils sont considérés comme étant les produits de fusion de l’encaissant, induits par la mise en place en profondeur des granites à biotite d’influence mantellique au cours de l’extension (D3), par effondrement gravitaire de la chaîne au Stéphanien inférieur.

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Keywords : Shrimp ages, Variscan intrusions, NE Iberia, Diorite, Leucogranite, Biotite granite

Mots clés : Datations Shrimp, Intrusions Varisques, Nord-Est de l’Espagne, Diorite, Leucogranite, Granite à biotite

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