Abstract

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 Voring 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.

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