HR: 1330h
AN: T12D-0498    [PDF]
TI: Opening of the Arctic-North Atlantic Gateway
AU: * Engen, O
EM: oyvind.engen@geo.uio.no
AF: Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, Oslo, 0316 Norway
AU: Faleide, J I
EM: j.i.faleide@geo.uio.no
AF: Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, Oslo, 0316 Norway
AU: Eldholm, O
EM: olav.eldholm@geo.uib.no
AF: Department of Earth Science, University of Bergen, Allegaten 41, Bergen, 5007 Norway
AU: Breivik, A
EM: a.j.breivik@geo.uio.no
AF: Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, Oslo, 0316 Norway
AB: The $\sim$150 km wide Fram Strait between Svalbard and Greenland is the only deep-water connection between the Arctic and the world oceans. It is essential for the thermohaline `engine' of the North Atlantic circulation system, pulling warm surface water north along the European coasts while returning cold, saline bottom water from the Arctic. Moreover, it contains a series of short, ultra-slow spreading segments and right-lateral transform faults, connecting the Gakkel Ridge to the rest of the Mid-Atlantic Ridge system. While the ridges to the north and south started spreading near the Paleocene-Eocene transition ($\sim$55 Ma), the plate boundary between Svalbard and Greenland underwent shear and a transpressive orogeny. Only after the earliest Oligocene ($\sim$33 Ma), when the Greenland plate became attached to North America and the rotation pole moved, the entire plate boundary became divergent. However, the final opening of the Fram Strait gateway was delayed for several reasons: First, basement terraces on the western Svalbard margin were downfaulted post-Eocene, witnessing a pre-breakup crustal thinning period that may have lasted for 15-20 m.y. Second, transform segments formed continental bridges for several m.y. after breakup on the ridge segments; the deep-water passage was not established before continental outliers were separated by young oceanic crust across all transform faults. Third, the Hovgaard microcontinent, which was split off the western Barents Sea-Svalbard margin, may have restricted water circulation for some time. By integrating gravity, bathymetry, magnetic and reflection seismic data we locate the positions of present and extinct spreading axes, as well as the continent-ocean transition (COT) on the Svalbard side. The COT correlates with a steep gradient in the Bouguer gravity anomaly, which is taken as a proxy COT on the sparsely surveyed Greenland side. By testing different rotation poles we arrive at a regionally consistent plate kinematic model from breakup to present. The model shows that deep-water conditions in the Fram Strait could not possibly occur before Late Miocene to Early Pliocene times (9.5-4.5 Ma). If so, the far-field sedimentary record needs to be re-examined for independent corroboration of a young, major, deep-water gateway through the Fram Strait.
DE: 3010 Gravity
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 4267 Paleoceanography
DE: 9315 Arctic region
SC: Tectonophysics [T]
MN: 2003 Fall Meeting