The World’s biggest relay ramp: Hold With Hope, NE Greenland

Abstract

Fault interaction in the Hold With Hope region of NE Greenland occurs between basin-margin faults that have a separation of about 100 km, with the relay ramp covering an area of about 25 000 km 2. This structure is therefore much larger than previously described relay ramps, showing that interaction between normal faults can occur over large areas and can control deformation across a region. The Western Fault Zone links north and eastwards with the Hochstetters Forland Fault via the Gauss Halvø Fault. These faults that control the relay ramp have kilometre-scale throws, juxtaposing Pre-Caledonian basement against Upper Palaeozoic and Mesozoic cover. The relay ramp initiated during the Devonian, but was at least partially breached at the end of the Devonian or beginning of the Carboniferous. Beds in the relay ramp are tilted towards the footwall, this tilt being similar to the results of recent numerical models of interacting normal faults. The relay ramp is affected by faults that are synthetic to, and that link, the basin-margin faults. These breaching faults suggest that stresses can interact over distances of at least 100 km. This model explains variations in the depth of the Moho across Kong Oscar Fjord. The basin-margin faults may be linked at depth, passing down into a relatively shallow detachment, or into a lower-crustal shear zone. Alternatively, the faults may not be directly connected at depth, but pass down into a zone of distributed ductile deformation.