Development of the Jan Mayen microcontinent by linked propagation and retreat of spreading ridges

Abstract

The Jan Mayen microcontinent lies between the active Kolbeinsey Ridge spreading centre and the extinct Aegir Ridge spreading centre in post-Paleocene oceanic crust to the north of Iceland. Uncertainties concerning the age of seafloor magnetic anomalies and the precise extent of oceanic crust in this segment of the northern North Atlantic have hindered attempts to model the spreading history. Here, we propose a new, geometrically self-consistent spreading model that uses a single set of rotation poles for the entire northern North Atlantic. In our model, the Jan Mayen microcontinent separated sequentially from the East Greenland margin during Oligocene time as a consequence of stepwise northward propagation of the Kolbeinsey Ridge and simultaneous northward retreat of the Aegir Ridge. The ridge tips were linked by a fracture zone that was periodically replaced by a new fracture zone to the north, resulting in balanced propagation/retreat of the spreading ridges and segmentation of intervening oceanic and microcontinent lithosphere. Spreading azimuths remained parallel with the West Jan Mayen Fracture Zone through the propagation/retreat phase. A number of possible fracture zones of the appropriate orientation can be identified that cut both the microcontinent and the occanic crust to the east. Systematic sinistral offset across these fracture zones produces an apparent counterclockwise rotation of the microcontinent with respect to the adjacent continental margins, whereas structural trends within the Jan Mayen microcontinent are not rotated appreciably. At least two factors appear to have been important in initiating the Kolbeinsey Ridge, and thus creating the Jan Mayen microcontinent: (1) the geometry of the plate boundary generated between Europe and Greenland at continental break-up (chron 24R), with the Aegir Ridge significantly offset to the east with respect to the Mohns and Reykjanes ridges; (2) a change of spreading azimuth, which acted to lock the transform system that had previously connected the southern tip of the Aegir Ridge with the northern end of the Reykjanes Ridge. The thermal effect of the Iceland plume on the overlying plates probably played little part in microcontinent generation, although the gravitational effect of the plume may have been significant.