Evidence for pre-Cenozoic extension in the eastern Main Ranges of the southern Canadian Rockies

Research in the Canadian Rocky Mountain Parks reveals that normal faults within the eastern Main Ranges of the southern Canadian Rockies, traditionally associated with postcontractional transtension during the Paleogene Period, likely originated much earlier—during Carboniferous and Permian rifting. This rifting separated pericratonic terranes from North America, forming the Slide Mountain Ocean. Unlike other regions where such extensional faults are obscured by later tectonic events, this area preserves these ancient structures due to Cretaceous to Paleogene contraction that transported them over unattenuated continental crust without significant overprinting. Detailed field mapping of deformation adjacent to normal fault surfaces provides critical evidence for this pre-Cenozoic extension, challenging prevailing interpretations and offering new insights into the tectonic evolution of the Canadian Rockies.

Taerum, R. L. (2022). Evidence for pre-Cenozoic extension in the eastern Main Ranges of the southern Canadian Rockies. Geosphere, 18(3), 1152–1176. https://doi.org/10.1130/ges02347.1