THE NORTHERN CORDILLERA - TOWARDS RESOLUTION OF CONTRADICTORY MODELS

Paleogeographic and tectonic models of Northern Cordilleran geological evolution are contradictory. Some feature large-scale margin parallel displacements of some or most of the orogen in the mid to Late Cretaceous. Most do not. What is not contradictory is the data. There is only one geological ‘history’ of the Cordillera. This history is recorded in the crustal rocks exposed at the surface and in the Cordilleran lithosphere and sub-lithospheric mantle. It is our reading of this record, through geological and geophysical interrogation of the crust and mantle, that is problematic, not the data. Hence reconciliation of the data used to argue for and against large-scale translations is possible. But it is proving to be a difficult task. Here I focus on three points including: 1) the implications of the Late K Carmacks Group; 2) the veracity of the stratigraphic correlations that tie the Cordillera together; and 3) determining if the problem facing us is systemic as opposed to Cordilleran. 1) Paleomagnetic studies of the 70 Ma Carmacks Group yield consistently far-sided and clockwise rotated paleopoles that have been interpreted as requiring almost 2000 km of dextral margin-parallel translation relative to cratonic N America. What portion of the Northern Cordillera is constrained by the Carmacks Group to have moved north in the Late Cretaceous, and where is the eastern boundary of this domain? 2) Stratigraphic correlations of Precambrian and Paleozoic strata have been used to tie much of the orogen to adjacent cratonic N America. Particularly compelling are the Proterozoic through lower Paleozoic stratigraphic ties that have been established in southern Alberta and BC (McMechan et al., 2021) and which beg the question ‘is correlation data or interpretation?’ 3) Is our inability to reconcile paleomagnetic and geological data within the Cordillera a uniquely Cordilleran problem? Or are we facing a systemic failure? If so, analysis of orogenic belts elsewhere on Earth and of different ages should be plagued by similar problems. Are they?