A KINEMATIC MODEL FOR IAPETUS OCEAN CLOSURE

Since the earliest days of plate tectonics, the evolution of the northern Appalachians and the Caledonides of the British Isles has served as a type example of the 'Wilson cycle' of ocean closing and opening. Orogen development has been illustrated using cross-section time-slices. This approach is valuable, but it leads to implicit assumptions that: (i) subduction was initiated at previously 'passive' continental margins; (ii) convergence was mainly orthogonal; and (iii) terranes and zones had ribbon-like geometry extending parallel to continental margins.

The post-Pangea tectonic evolution of the Earth provides little support for these assumptions. We use the software GPlates to propose alternative kinematic models for the Northern Appalachians and the Caledonides of Britain and Ireland that operate on the surface of a sphere. We first restore the effects of Mesozoic extension and late Paleozoic strike-slip using previous estimates. We then attempt to reconstruct possible Ordovician to Silurian terrane paths that honor paleomagnetic data, provenance evidence of terrane linkage, and suggested positions of peri-Gondwanan terranes along the margin of Amazonia – West Africa. The results suggest that terranes attributed to Ganderia and associated peri-Gondwanan arcs crossed the Iapetus in at least four pieces. Portions of "Ganderian" and "Avalonian" continental crust may have travelled together after being juxtaposed during Monian/Penobscottian interaction on the margin of Gondwana, that involved involving along-margin strike-slip, transpression, and/or transtension.