Ordovician fragmentation of Gondwana : Integrated magmatic – sedimentary – structural record of the Variscan domain
Résumé
Fragmentation of northwestern Gondwana took place in a context of massive and
widespread magmatism during the Ordovician. With the improvement of U-Pb dating
techniques, Ordovician plutonic and volcanic rocks have been increasingly documented
throughout the Variscan orogen of Europe. The origin of this magmatism is largely debated if
not largely conjectural. But it implies a lithospheric and most probably asthenospheric
reorganization of the Variscan domain of Gondwana, directly impacting the later convergence
between Gondwana and Laurussia. The Ordovician sedimentary record, and particularly that
of the “Sardic” unconformity also poses the issue of the potential links between external and
internal geodynamics via lithospheric deformation during the Ordovician crisis.
The Ordovician crisis is richly documented throughout the Variscan belt, but mainly at
numerous localities and mostly from a monodisciplinary perspective, notwithstanding the fact
that the structural environment of Ordovician sediments, plutons and volcanics has rarely
been investigated. Our project (ORDISCO) aims at evaluating the coupling between internal
geodynamics, crustal deformation and the sedimentary record during dynamic reorganization
of the Gondwana margin later involved in the Variscan collision. It involves implementing a
harmonized geodatabase gathering the magmatic, structural, sedimentologic, stratigraphic,
and geochronological information on the Ordovician period at the scale of the Variscan belt of
Europe. The project also includes the detailed multidisciplinary study of three key regions of
the inner part of the Gondwana margin located in Southern France and Spain and the
reexamination of the reference sites in Sardinia.
The present contribution aims at presenting the geodatabase and the progress made at
building the magmatic / geochronological sub-base, as well as the first stratigraphic,
geochronological and structural results from the Variscan foreland in SE France