New U-Pb monazite, zircon, and xenotime ages date the Late Carboniferous crystallization of the anatectic Vialais granite in the Montagne Noire Axial Zone and the high-temperature deformation and metamorphism of the augen gneiss (Ordovician granite protolith) from which the granite was likely derived. The U-Pb monazite ages obtained from the augen gneiss (308. ±. 3. Ma), late kinematic Vialais granite (303. ±. 4. Ma), and post-kinematic leucogranite (298. ±. 2. Ma), bracket the high-temperature deformation and metamorphism at ~. 310-300. Ma, clearly postdating regional contraction and nappe emplacement (>. 320. Ma). The planar-linear and locally linear fabrics in the augen gneiss outline a regional-scale double dome structure (Caroux and Espinouse sub-domes) containing smaller (km-scale) upright folds. Compared to the Caroux sub-dome, the larger, migmatitic Espinouse sub-dome contains abundant leucosome, leucogranite bodies and late-kinematic intrusions (Vialais granite). The Vialais granite displays a weak magmatic foliation that defines the main layering of the Espinouse migmatite. Ellipsoidal quartz-sillimanite nodules concentrated above the roof of the granite recorded an increment of strain (vertical shortening, E-NE elongation) during granite emplacement and crystallization, consistent with the extension event that exhumed the domes. These new geochronological and structural data suggest that the Montagne Noire double dome formed in a pull-apart structure within a dextral strike-slip system. Upright folding in the sub-domes has been traditionally assigned to a regional contraction event; alternatively, we propose that local contraction is associated with the convergence of low-viscosity crust beneath the upper crust pull-apart. Dynamic models of extension of hot crust indicate that contraction at depth is generated by flow of low-viscosity orogenic crust converging and rising to fill the gap created by upper crust extension. This interpretation solves the long-standing problem of apparent coeval contraction and extension in the Montagne Noire double dome and establishes migmatite dome emplacement in strike-slip corridors as a style of late Variscan tectonics.
Bibliographical noteFunding Information:
Teyssier, Whitney, and Rey acknowledge support from the National Science Foundation grant EAR-1050020 . Detailed review by Olivier Vanderhaeghe and two anonymous reviewers helped improve the manuscript.
© 2014 Elsevier B.V.
Copyright 2015 Elsevier B.V., All rights reserved.
- Extensional tectonics
- Gneiss dome
- ID-TIMS and LA-ICP-MS U/Pb dating
- Late carboniferous crustal flow
- Partial melting
- Variscan belt