COMPLEX TECTONICS OF THE GONDWANA-LAURUSSIA PLATE BOUNDARY ZONE – INTERFERENCE OF RELATIVE PLATE MOTION AND LATERAL ESCAPING LITHOSPHERIC BLOCKS (Invited Presentation)

Western Pangea resulted from the continental collision of the plates of Gondwana and Laurussia from early Devonian to Permian time. The evolved orogens at the plate boundary zone differ significantly in respect of timing and tectonics. This is caused by the diachronous, zipper style closure of the Rheic Ocean and the existence of a Peri-Gondwana promontory, i.e., the Armorican Spur. The presented tectonic model explains the evolution as well as the complex strain pattern with the sequential change of global plate kinematics in combination with regional scale decoupling of lithospheric blocks. Whereas the architecture of the Alleghanian fold and thrust belts predominantly displays the plate motion of Gondwana relative to Laurussia, the recurrent interference with lateral escaping lithospheric blocks is the underlying reason for the arcuate shape of the European Variscides. The principal steps are as follows.

Early Devonian collision of the Armorican Spur with Laurussia initiated the Acadian / Early Variscan orogeny in Western Europe coeval with transpressional tectonics in the Northern Appalachians. Late Devonian plate tectonic reorganization caused NW directed lateral escape of a lithospheric block in Brittany coeval with ongoing NE directed subduction-accretion tectonics in Central Europe. Subsequent W-directed collision of decoupled huge E-Peri-Gondwana lithospheric block with already accreted crust of the western shelf resulted in pervasive transpressional tectonics of the W-European Variscides and resulted in the Late Variscan Ibero-Armorican Arc.

Latest Carboniferous detachment of the Gondwana plate south of Europe terminates the Variscan orogeny. Ongoing collision of Gondwana and Laurussia occurred exclusively at the plate boundary segment of Western Gondwana and North America, finally shaping the fold and thrust belts of the Southern Appalachians and the Ouachita-Sonora-Marathon belt.

References: Kroner and Romer, 2013, Gondwana Research, 24; Kroner et al., 2016, Tectonophysics, 681; Stephan et al., 2018, Geological Magazine; Willner et al., 2018, Tectonophysics