The role of the Spitsbergen shear zone in determining morphology,segmentation and evolution of the Knipovich Ridge |
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| Authors: | Crane Kathleen Doss Hany Vogt Peter Sundvor Eirik Cherkashov Georgy Poroshina Irina Joseph Devorah |
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| Institution: | (1) Department of Geography, Hunter College, CUNY, 695 Park Avenue, New York, NY 10021, USA;(2) Marine Physics, Code 7420, Naval Research Laboratory, Washington, DC 20375, USA;(3) Department of Solid Earth Physics, University of Bergen, Allegaten 41, Bergen, Norway;(4) VNIIOkeangeologia, 1 Anglyskiy Prospekt, St. Petersburg, Russia;(5) Naval Oceanographic Office, Code N92, 1002 Balch Blvd. Stennis Space Center, MS 39522, USA |
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| Abstract: | In 1989–1990 the SeaMARC II side-looking sonar and swath bathymetric system imaged more than 80 000 km2 of the seafloor in the Norwegian-Greenland Sea and southern Arctic Ocean. One of our main goals was to investigate the morphotectonic
evolution of the ultra-slow spreading Knipovich Ridge from its oblique (115° ) intersection with the Mohns Ridge in the south
to its boundary with the Molloy Transform Fault in the north, and to determine whether or not the ancient Spitsbergen Shear
Zone continued to play any involvement in the rise axis evolution and segmentation.
Structural evidence for ongoing northward rift propagation of the Mohns Ridge into the ancient Spitsbergen Shear Zone (forming
the Knipovich Ridge in the process) includes ancient deactivated and migrated transforms, subtle V-shaped-oriented flank faults
which have their apex at the present day Molloy Transform, and rift related faults that extend north of the present Molloy
Transform Fault. The Knipovich Ridge is segmented into distinct elongate basins; the bathymetric inverse of the very-slow
spreading Reykjanes Ridge to the south. Three major fault directions are detected: the N-S oriented rift walls, the highly
oblique en-echelon faults, which reside in the rift valley, and the structures, defining the orientation of many of the axial
highs, which are oblique to both the rift walls and the faults in the axial rift valley.
The segmentation of this slow spreading center is dominated by quasi stationary, focused magma centers creating (axial highs)
located between long oblique rift basins. Present day segment discontinuities on the Knipovich Ridge are aligned along highly
oblique, probably strike-slip faults, which could have been created in response to rotating shear couples within zones of
transtension across the multiple faults of the Spitsbergen Shear Zone. Fault interaction between major strike slip shears
may have lead to the formation of en-echelon pull apart basins. The curved stress trajectories create arcuate faults and subsiding
elongate basins while focusing most of the volcanism through the boundary faults. As a result, the Knipovich Ridge is characterized
by Underlapping magma centers, with long oblique rifts.
This style of basin-dominated segmentation probably evolved in a simple shear detachment fault environment which led to the
extreme morphotectonic and geophysical asymmetries across the rise axis. The influence of the Spitsbergen Shear Zone on the
evolution of the Knipovich Ridge is the primary reason that the segment discontinuities are predominantly volcanic.
Fault orientation data suggest that different extension directions along the Knipovich Ridge and Mohns Ridge (280° vs. 330°,
respectively) cause the crust on the western side of the intersection of these two ridges to buckle and uplift via compression
as is evidenced by the uplifted western wall province and the large 60 mGal free air gravity anomalies in this area.
In addition, the structural data suggest that the northwards propagation of the spreading center is ongoing and that a `normal'
pure shear spreading regime has not evolved along this ridge.
This revised version was published online in November 2006 with corrections to the Cover Date. |
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