BUILDING KINEMATIC MODELS FOR IAPETUS OCEAN CLOSURE

Appalachian-Caledonide orogen development has been traditionally illustrated using cross-sections showing terrane accretion and collision over time. This approach is valuable but leads to implicit assumptions: (i) subduction was initiated at passive continental margins; (ii) convergence was mainly orthogonal; (iii) terranes and zones had ribbon-like geometry parallel to continental margins; and (iv) present-day orogen geometry is a valid "end point" for reconstructions. Post-Pangea tectonic evolution provides little support for these assumptions. We will use GPlates software to display alternative, more actualistic kinematic models.

We will include in this analysis several previously under-utilized data sets:

1) Estimates of late Paleozoic and Mesozoic plate motions, to restore a valid mid-Devonian geometry from which to build back in time;

2) Reviews of legacy biostratigraphic data using calibrated time scales to place sedimentary units accurately relative to isotopically dated igneous units;

3) A review of paleomagnetic information including both declinations and inclinations, so as to evaluate terrane-scale changes in both orientation and latitude;

4) A compilation of detrital zircon data using new display methods to show proximity of terranes to major continental blocks that are the best candidates for sedimentary provenance.

Preliminary results suggest that terranes attributed to Ganderia and associated Gondwana-derived arcs crossed the Iapetus in several pieces, arriving at the Laurentian margin at different times from Ordovician to Devonian. Portions of "Ganderian" and "Avalonian" continental crust may have travelled together after being juxtaposed during Penobscottian convergence on the margin of Gondwana. The Taconian Orogeny is explained as the result of a diachronous arc-continent collision that involved both Laurentia-derived and Gondwana-derived units. It was followed by subduction-polarity reversal at the Laurentian margin. Salinian deformation resulted from subduction-accretion of terranes at this margin, over a period lasting from the Late Ordovician to the Ludlow. Acadian deformation resulted from motion at an Early Devonian along-margin boundary that may have varied from sinistral transpression in New England to ideal strike slip in Britain and Ireland.