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Thermal evolution of the western Svalbard margin
Authors:K Crane  E Sundvor  J -P Foucher  M Hobart  A M Myhre  S LeDouaran
Institution:(1) Dept. of Geology and Geography, Hunter College, CUNY 695, Park Ave., 10021 N. Y., NY, USA;(2) Lamont-Doherty Geological Observatory, 10964 Palisades, NY, USA;(3) Seismological Observatory, Allegaten 41, Univ. of Bergen, 5000 Bergen, Norway;(4) IFREMER, Centre de Brest, BP 337, 29273 Brest, France;(5) Department of Geology, University of Oslo, Blindern, Postboks 1047, Oslo 3, Norway;(6) Societe Nationale Elf Aquitaine, Tour Generale, Cedex 22, 92088 Paris, La Defense, France
Abstract:The northern Norwegian-Greenland Sea opened up as the Knipovich Ridge propagated from the south into the ancient continental Spitsbergen Shear Zone. Heat flow data suggest that magma was first intruded at a latitude of ap75° N around 60 m.y.b.p. By 40–50 m.y.b.p. oceanic crust was forming at a latitude of 78° N. At ap12 m.y.b.p. the Hovgård Transform Fault was deactivated during a northwards propagation of the Knipovich Ridge. Spreading is now in its nascent stages along the Molloy Ridge within the trough of the Spitsbergen Fracture Zone. Spreading rates are slower in the north than the south. For the Knipovich Ridge at 78° N they range from 1.5–2.3 mm yr-1 on the eastern flank to 1.9–3.1 mm yr-1 on the western flank. At a latitude of 75° N spreading rates increase to 4.3–4.9 mm yr-1.Thermal profiles reveal regions of off-axial high heat flow. They are located at ages of 14 m.y. west and 13 m.y. east of the northern Knipovich Ridge, and at 36 m.y. on the eastern flank of the southern Knipovich Ridge. These may correspond to episodes of increased magmatic activity; which may be related to times of rapid north-wards rise axis propagation.The fact that the Norwegian-Greenland Sea is almost void of magnetic anomalies may be caused by the chaotic extrusion of basalts from a spreading center trapped within the confines of an ancient continental shear zone. The oblique impact of the propagating rift with the ancient shear zone may have created an unstable state of stress in the region. If so, extension took place preferentially to the northwest, while compression occurred to the southeast between the opening, leaking shear zone and the Svalbard margin. This caused faster spreading rates to the northwest than to the southeast.
Keywords:transform margins  heat flow  ridge propagation
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