Orogenic polarity, paleo-magnetic constraints and updated geochronology of high to ultra high-pressure metamorphism: towards a re-interpretation of the evolution of the French Variscan belt?

In mountain belts, one the one hand, the method to restore the paleopositions of landmasses, and thus oceanic domains, is paleomagnetism, combined with high-resolution geochronological data. As far as the Palaeozoic is concerned, we are fortunate to benefit of the so-called unified full plates reconstruction models (i.e. paleomagnetic databases consistent with coherent plate boundaries kinematics, mantle dynamics and geologic features, see for example Domeier and Torsvik, 2017 for a general discussion).

On the other hand, deciphering orogenic polarity requires the combination of different geophysical methods. Regarding the European Variscan belt, a synthetic overview of results and interpretations of various methods of geophysical imagery is now available ( Edel et al, 2018; Schulmann et al., 2022).

These two types of data constitute robust points of reference that any orogenic evolution model must respect at least in the first order.

In the last decade, in the French Variscan belt, significant advances linking petrological and geochronological records have been performed, especially on high to ultra-high pressure metamorphic rocks. In addition, new observations have confirmed the occurrence and extension of magmatic arcs and back-arcs systems active during Devonian and Carboniferous times.

We present and discuss a review of all these new data and their confrontation with the available robust paleomagnetic and geophysical crustal-scale constraints. This analysis leads us to a revision, and sometimes a radical re-evaluation, of the orogenic evolution models hitherto proposed to interpret the evolution of the French part of the European Variscan belt.

References:

Edel JB, Schulmann K, Lexa O, Lardeaux JM. 2018. Late Palaeozoic palaeomagnetic and tectonic constraints for amalgamation of Pangea supercontinent in the European Variscan belt. Earth Sciences Review, 177:589−612

Domeier M, Torsvik TH. 2017. Full-plate modelling in pre-Jurassic time. Geological Magazine, 156(2): 261−280.

Schulmann, K., Edel, J.B., Martinez-Catalàn, J.R., Mazur, S., Guy, A., Lardeaux, J.M., Lexa, O., Ayarza, P., Palomeras, I. 2022. Tectonic evolution and global architecture of the European Variscan belt constrained by geophysical data. Earth Sciences Review, 234, 104195.