TECTONIC RECONSTRUCTIONS OF NORTH AMERICA AND CORDILLERAN TERRANES- A PALEOMAGNETIC PERSPECTIVE WITH PALEOZOIC AND MESOZOIC EXAMPLES

Using rocks from both tectonostratigraphic terranes and those associated with cratonic portions of tectonic plates, paleogeographic reconstructions can be made using paleomagnetism. The ability to determine the paleolatitude of rocks from a given terrane, and to compare this with predicted locations derived from a given tectonic model makes paleomagnetism an interesting tool for terrane analysis. The focus of the presentation will be an evaluation of paleogeographic models for North America and the Alexander/Wrangellia terrane, with examples from Paleozoic and Mesozoic time.

For North America, a significant number of paleomagnetic results from cratonic rocks are available, with some important time intervals being poorly represented. To augment these data several composite apparent polar wander path (APWP) models for NA have been constructed using results from other plates rotated into NA coordinates. These composite APWPs (Besse and Courtillot, 2002, Enkin 2006, Torsvik et al, 2008, Kent and Irving 2010, Cocks and Torsvik 2011) will be compared with APWPs that rely only on NA-derived data. Several complications are highlighted- for sedimentary rocks the possibility of inclination error exists (and correction methods are variably successful), many results are from deformed craton margins and so may include recognized or suspected rotations, and many APWP compilations include either lengthy still-stands (during which NA experienced little or no motion relative to the spin axis) or rapid APW that may suggest true polar wander.

Data from tectonostratigraphic terranes are abundant for some of the larger terranes, but are poor or non-existent for many others. Complications that will be highlighted include the common association between remagnetization and deformation, the often poor paleomagnetic behavior of the clastic sediments that are common to many of these terranes, and issues of internal deformation that can complicate data interpretation. Despite these complications, robust sets of data are available. Evaluation of competing paleogeographic models for the Alexander and associated arc terranes during Siluro-Devonian time (Wright and Wyld, 2006, Colpron et al, 2009, Cocks and Torsvik, 2001, and Beranek et al, 2013), and for Wrangellia and associated terranes during the Mesozoic will be made.