HR: 15:10h
AN: T52E-07    [PDF]
TI: Crustal and Upper Mantle Structure of the Ultra-slow Spreading Gakkel Ridge
AU: * Schmidt-Aursch, M
EM: mschmidt@awi-bremerhaven.de
AF: Mechita C. Schmidt-Aursch, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, 27568 Germany
AU: Jokat, W
EM: jokat@awi-bremerhaven.de
AF: Wilfried Jokat, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, 27568 Germany
AB: The 1800 km long Gakkel Ridge (Arctic Ocean) shows full spreading rates between 13 mm/yr north of Greenland and 6 mm/yr near its termination in the Laptev Sea. It is the slowest-spreading mid-oceanic ridge worldwide, and therefor plays a key role in understanding melt generation and crustal accretion processes. The joint AMORE expedition investigated the rigde in summer 2001 with the two research icebreakers RV Polarstern and USCGC Healy. Several geophysical and petrological experiments have been conducted including refraction seismic profiling along the rift valley and detailed sampling of the sea floor. Analysis of the rock samples and forward modelling of the wide-angle seismic data resulted in a clear division of the ridge in three parts with completely different structural characteristics. First results of a helicopter-based magnetic survey gave evidence for long-term focused magmatism along some parts of the ridge. The seismic data yielded also an exceptional thin oceanic crust with thicknesses not higher than 3 km and seismic velocities well below 6.4 km/s. Seismic velocities in the upper mantle are with values around 7.8 km/s also very low. The velocity models gave direct constraints for a 3D forward modelling of gravity data based on the 5-minute-grid of the Arctic Gravity Project. The crustal thickness shows only little variations along the rift valley, but perpendicular to the ridge the thickness varies between vanishingly thin and about 6 km. The density models off-axis strongly depend on the assumed temperature structure of the upper mantle. We will present several 3D density models of the oceanic crust and upper mantle to discuss different melt generation processes along the ridge.
DE: 1744 Tectonophysics
DE: 3025 Marine seismics (0935)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting