Reconstructing the Neoproterozoic-lower Paleozoic Franklinian Margin of the Northwestern Canadian Arctic

Thomas Hadlari

New data from northwest Victoria Island are integrated with a synthesis of the Franklinian margin to infer the rift geometry during the breakup of Rodinia. Two fault trends at Victoria Island are postulated to have been active in the Neoproterozoic. (1) North and northwest-striking syn-magmatic fault zones host dykes of the Franklin magmatic event that indicate fault activity at ca. 720 Ma (Bedard et al. 2012); (2) A corridor of ENE striking normal faults is well developed and cuts the basal Cambrian unconformity, Cambrian strata overlie different stratigraphic intervals of the Shaler Supergroup across those faults, indicating post-Shaler, pre-Cambrian offset. The distribution of facies and Cambrian strata themselves are suggestive of deposition within paleotopographic lows, similar to patterns on the mainland to the south. Northwest of Victoria Island, Neoproterozoic and Cambrian facies define shelf (Arctic Platform) and offshore (Deep Water Basin) regions. We interpret the NE trend of the Cambrian facies transition to parallel the overall trend of the rifted margin. There is an orthogonal change in trend of the platform-offshore transition near Prince Patrick and Melville islands that projects offshore. Banks Island was thus part of the Arctic Platform. We relate the northwest-striking faults on Victoria Island that were active at 720 Ma to a transfer zone that separated the Arctic Platform on Banks and Victoria islands from the Deep Water Basin underlying the Sverdrup Basin to the northeast. The northeast-striking faults on Victoria Island are similarly correlated to the overall trend of the Franklinian margin. It has been proposed previously that the Deep Water Basin was underlain by oceanic crust. Now, the Deep Water Basin is defined by Cambrian facies, which are not indicative of the entire lithosphere. Seismic data show clinoforms that prograded into the basin, but are less than a second in thickness, not at the scale of a continental margin. Well basinward of the offshore facies boundary are Neoproterozoic-Cambrian(?) shallow marine facies at northern Axel Heiberg Island. Those peritidal deposits and associated mafic volcanic rocks are located on the “other side” of the Deep Water Basin and are therefore inconsistent with oceanic crustal affinity. We raise the question, did the Franklinian Deep Water Basin overlie continental crust, have an origin during Neoproterozoic rifting, and was it flanked by the actual continental margin platform with volcanic rocks to the northwest?