ABSTRACT Ellef Ringnes Island in the western Queen Elizabeth Islands near the Canadian Polar margin is characterized by intrusions of Cretaceous mafic sills and dikes related to the Canadian portion of the High Arctic Large Igneous Province (HALIP) and the presence of a unique network of NNE–SSW and WSW–ENE striking steep faults. The exposed dikes on northern Ellef Ringnes Island are mostly oriented parallel to the NNE–SSW faults according to the radiating dike swarm of the HALIP. The studied sills and dikes are geochemically very homogeneous and probably related to the same intrusion event at ca. 121 Ma. They share geochemical similarities with other tholeiitic basaltic rocks related to the first stage of the HALIP (ca. 130–120 Ma) that are exposed on Axel Heiberg and northern Ellesmere islands. All these suites were probably generated from a common large magmatic center related to a mantle plume. The NNE–SSW striking faults are characterized by dextral strike-slip kinematics active after ca. 100 Ma (after the intrusion of the Early Cretaceous sills and dykes and the deposition of the Christopher Formation) and before the deposition of the Neogene Arctic continental terrace wedge. However, they cannot be related to the dextral strike-slip regime parallel to the continental margin during stage 2 of the Eurekan deformation in the Late Eocene. Instead, the NNE–SSW dextral faults may represent dextral antithetic Riedel faults of a wide, NE–SW striking, anastomosing strike-slip fault zone along the northern continental margin of North America, which was possibly active during Eurekan stage 1 in the Early Eocene.