The Neoproterozoic Hekla Sund Basin, eastern North Greenland: A pre-lapetan extensional sequence thrust across its rift shoulders during the Caledonian orogeny

The Vandredalen thrust sheet forms the allochthonous Caledonian front in Kronprins Christian Land, eastern North Greenland. It transported Neoproterozoic shallow marine, arkosic sediments of the Rivieradal Group and shelf sediments of the Hagen Fjord Group across parautochthonous Neoproterozoic-Ordovician sediments on the foreland. The thrust sheet roots to the east along the Brede Spærregletscher-Hekla Sund lineament and has a demonstrable westwards displacement of c. 40 km. A large part of that displacement (c. 22 km) is achieved on a single structure, the Vandredalen thrust, but this is only one of a linked system of thrusts which involve parautochthonous thin-skinned thrust sheets to the west and thicker skinned thrust sheets now exposed in the east. Conodont geothermometry suggests that the thick-skinned thrust sheets formerly extended westwards above the Vandredalen thrust sheet at higher structural levels. Restoration of the displacement on the thin-skinned thrusts reveals the Rivieradal Group to be a Neoproterozoic syn-rift sequence deposited in an eastwards-facing extensional half-graben (Hekla Sund Basin) which originally lay immediately to the east of the Brede Spærregletscher-Hekla Sund lineament. The transgressive Hagen Fjord Group represents a period of post-rift thermal re-equilibration in latest Riphean time and the youngest units in the group overstep the original rift shoulder. The Hekla Sund Basin represents another example of the rift-sag episodes which are an important feature of the pre-lapetan evolution of the Laurentian margin successions and comparisons are made with coeval basins in Scotland and Svalbard.