From Devonian extensional collapse to early Eocene continental break‐up: an extended transect of the Kejser Franz Joseph Fjord of the East Greenland margin

SUMMARY Seismic investigations along East Greenland's Fjord Region completed during the last decade provide fundamental insights into the region's crustal structure and tectonic history. A summary of models along a transect through the Kejser Franz Joseph Fjord provides a view from the Precambrian Shield to the Eocene oceanic crust. We conclude that a change of rifting geometry from an upper‐ to a lower‐plate‐style margin occurred in early Mesozoic times and formed the >350‐km‐wide rift zone. Despite the demonstrated asymmetry of the northeast Greenland and conjugate Vøring margins, the change of rift geometries and the direction of rift jumps remain debatable. A combined model for productivity and duration of magmatism is proposed for the northeast Greenland fjord region. We suggest that magmatism started slowly at 58.8 ± 3.6 Ma with a production rate of 1.5 × 10 −4 km 3 km −1 a −1 , which is similar to the productivity of onshore upper and lower lava sequences on the Geikie Plateau. A peak of 9.4 × 10 −4 km 3 km −1 a −1 for 0.5 Myr, and a subsequent productivity of 4.4 ± 0.3 × 10 −4 km 3 km −1 a −1 for 2.5 Myr between 53.3 and 50.8 Ma, produced the majority of melt, but break‐up did not occur immediately afterwards. Continuous production of melt, similar to the rate of ocean spreading until C22 (∼50 Ma), contributed to massive magmatic underplating until eventual break‐up at 50 Ma. The volumes and production rates show similarities to those obtained from a profile off the southeast Greenland margin but with a major difference in a smaller regional spatial extent.