Abstract
The Paleozoic French Variscan Belt in Massif Central and Massif Armoricain is a collision belt that provides a good example of a suture zone where ophiolites are rare, and the frontal (i.e., the magmatic arc) part of the upper plate is not present. In the lower plate (or Gondwana), the continental rocks are subdivided into an Upper Gneiss Unit (UGU) and a Lower Gneiss Unit (LGU). The UGU experienced a highâpressure (and likely ultraâhighâpressure) metamorphism followed by crustal melting during their exhumation. New chemical UâThâPb monazite ages and ionâprobe UâPb zircon ages on migmatites allow us to constrain the PâTât paths followed by the UGU and LGU. By comparison with thermomechanical experiments, a possible geodynamic evolution scenario can be proposed for the Variscan convergence. The highâcompression regime of continental subduction developed during the initial subduction of the northern margin of Gondwana under Armorica in Silurian times. This induced the formation of a new subduction zone in the backâarc basin, which is the youngest, hottest, and thus mechanically the weakest part of the overriding plate. As a result, the arcâbackâarc basin domain has been almost totally subducted below Armorica. Only a limited part of the backâarc basin rocks remains exposed in the Devonian StâGeorgesâsurâLoire Unit. Subsequently, the continental subduction of Gondwana resumed with a steeper dip associated with lowâcompression regime that in turn allowed the highâpressure rocks to be exhumed and partly melted in Late Devonian times. Such a scheme depicts quite well the complexity of the Variscan Belt.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.