Development of the Jan Mayen microcontinent by linked propagation and retreat of spreading ridges
Robert A. Scott1, L.A. Ramsey2, S.M. Jones3, S. Sinclair1 & C.S. Pickles4
1
CASP, Department of Earth Sciences, University of Cambridge, West Building, 181A Huntingdon Road, Cambridge CB3 0DH, UK2
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK3
Bullard Laboratories, University of Cambridge, Madingley Rise, Cambridge CB3 0EZ, UK4
ChevronTexaco, Woodhill House, Westburn Road, Aberdeen AB16 5XL, UKrobert.scott@casp.cam.ac.uk
Cenozoic oceanic crust north of Iceland contains an active spreading centre (the Kolbeinsey Ridge), an extinct spreading centre with pronounced apparent curvature (the Aegir Ridge), and an intervening continental fragment (the Jan Mayen microcontinent). Previous spreading models for this part of the Norwegian-Greenland Sea have invoked fan-shaped spreading geometries with different rotation poles to those used for coeval oceanic areas to the south and north. As a result of geometrical inconsistencies in these models, we have attempted to derive a self-consistent kinematic model that explains seafloor spreading for the entire northern North Atlantic using a single set of rotation poles.
In our model, spreading with a constant NW-SE azimuth occurred on the Mohns Ridge (north of the Jan Mayen Fracture Zone), Reykjanes Ridge (south of Iceland) and the Aegir Ridge from continental break-up at chron 24R to chron 18 time. During this interval, the Aegir Ridge was straight and parallel to the Mohns and Reykjanes ridges. Around chron 18-17 time, the spreading azimuth on all three ridges changed abruptly to a more WNW-ESE direction. From chron 17 to chron 6 time, stepwise northward propagation of the Kolbeinsey Ridge was balanced by stepwise northward retreat of active spreading on the Aegir Ridge, with the propagating and dying ridge tips linked by fracture zones. The balanced propagation/retreat resulted in curvature of the Aegir Ridge, fanning of magnetic anomalies formed at the Aegir Ridge, and apparent anticlockwise rotation of the Jan Mayen microcontinent by displacement along the linking fracture zones. Following the extinction of the Aegir Ridge around chron 6 time, spreading occurred on the Mohns, Kolbeinsey and Reykjanes ridges.
The initiation of the Kolbeinsey Ridge was intimately linked with the change of spreading azimuth at chron 18-17 time, 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. Individual episodes of northward propagation on the Kolbeinsey Ridge may have been promoted by pulses of Iceland plume activity. Dynamic elevation of the incipient Kolbeinsey Ridge with respect to the Aegir Ridge may have been the principal mechanism that promoted microcontinent formation.