Role of tectonic inheritance in the latest Cretaceous to Paleogene Eurekan Orogeny (NE Canadian Arctic)

The Eurekan Orogeny is a contractional deformational event that occurred during latest Cretaceous to Paleogene times along the eastern Canadian Arctic and northern Greenland, and which possibly reached as far as Svalbard (Figure 1). It was caused by the reactivation of the Late Devonian to Early Carboniferous Ellesmerian Orogen because of relative plate motions between Greenland and Ellesmere Island. De Paor et al. (1989) highlighted the atypical nature of the orogen when compared with the general structure of standard thrust and fold belts: it does not contain a metamorphic zone nor a well-developed foreland basin, the exposed rocks are younger towards the hinterland and the orogen is anomalously wide. Despite recent research in the region, the atypical nature of the Eurekan Orogen remains largely unexplained.

This study presents a set of restored cross-sections through Ellesmere and Axel Heiberg islands in order to discuss the structural development of the Eurekan Orogen. In the study area, Eurekan structures are characterised by easterly and south-easterly directed thrusts which involve different amounts of strike-slip. These thrusts incorporate Proterozoic to Mississippian rocks of the Ellesmerian Orogen, Mississippian to Late Cretaceous rocks of the Sverdrup Basin and latest Cretaceous to Paleogene syn-orogenic strata. Our structural restorations reveal that, besides the reactivation of Ellesmerian structures, the style of Eurekan deformation was significantly controlled by the tectonic inversion of structures related to Sverdrup Basin development (Figure 1).

During the Mississippian to Late Cretaceous, the structural evolution of the Sverdrup Basin was dominated by salt diapirs and extensional faults. The distribution and structural style of both the diapirs and the extensional faults were determined by the presence and extent of a Carboniferous salt layer at the base of the sedimentary succession. Diapirs were concentrated along the basin axis, where a thick Late Carboniferous salt layer was present. Generally, diapirs were associated with salt withdrawal minibasins that developed over autochthonous salt, except on southern Axel Heiberg Island, where the minibasins sank over an allochthonous salt canopy. Marginal areas of the basin, where no salt was deposited, were cut by Carboniferous to Jurassic extensional faults.

During the latest Cretaceous to Paleogene, Eurekan shortening resulted in the reactivation of earlier structures and subsidence in the Sverdrup Basin ended. The style of tectonic inversion was controlled by the amount of salt: extensional faults at the basin margin were inverted whilst in the basin centre the diapirs were squeezed and the minibasins continued subsiding. Some of the diapir walls formed thrust-welds that merged into larger thrusts detached at the base of the salt layer. Therefore, both the current thrust geometry and distribution were inherited from the Sverdrup Basin original structural framework. Tectonic inheritance explains both the anomalous width of the orogen and the younging of exposed statigraphic units towards the foreland (towards the basin centre) as well as the vergence of the orogen towards Greenland. In addition, the presence of salt at the base of the sedimentary succession helps to explain the total absence of a metamorphic zone.

Previous work in the area focused on differentiating Ellesmerian from Eurekan structures, which was important to constrain the regional tectonic framework. However, our study demonstrates that the style of Eurekan deformation on the Canadian Arctic was determined by the original structural framework of the Sverdrup Basin. This highlights the importance of tectonic inheritance in the development of thrust and fold belts.