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We investigate (i) margin-scale structural inheritance in rifts and (ii) the time scales of rift propagation and rift length establishment, using the East Greenland rift system (EGR) as an example. To investigate the controls of the underlying Caledonian structural grain on the development of the EGR, we juxtapose new age constraints on rift faulting with existing geochronological and structural evidence. Results from K-Ar illite fault dating and syn-rift growth strata in hangingwall basins suggest initial faulting in Mississippian times and episodes of fault activity in Middle-Late Pennsylvanian, Middle Permian, and Middle Jurassic to Early Cretaceous times. Several lines of evidence indicate a close relationship between low-angle late-to-post-Caledonian extensional shear zones (CESZs) and younger rift structure: (i) reorientation of rift fault strike to conform with CESZs, (ii) spatial coincidence of rift-scale transfer zones with CESZs, and (iii) close temporal coincidence between the latest activity (late Devonian) on the preexisting network of CESZs and the earliest rift faulting (latest Devonian to earliest Carboniferous). Late-to post-Caledonian extensional detachments therefore likely acted as a template for the establishment of the EGR. We also conclude that the EGR established its near-full length rapidly, i.e., within 4-20% of rift life. The "constant-length model" for normal fault growth may therefore be applicable at rift scale, but tip propagation, relay breaching, and linkage may dominate border fault systems during rapid lengthening.

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Supradetachment basins at passive rifted margins are a key witness of majorcontinental extension, and they may preserve a record from which the amount and rates of extension and metamorphic core complex exhumation may be reconstructed. These basins have mainly been recognised in back-arc and orogenic collapse settings, with few examples from rifted margins. Using 2D and 3D seismic reflection, wellbore, and gravity anomaly data, we here characterise the threedimensional structural and tectonosedimentary evolution of a spoon-shaped supradetachment basin that was formed in the necking domain of a rifted margin, EAGE MUÑOZ-BARRERAetal.