HR: 1330h
AN: T12A-0450    [PDF]
TI: Differing Forms of Continental Rifting on the Eurasian and Amerasian Margins of the Lomonosov Ridge, Arctic Ocean
AU: * Cochran, J R
EM: jrc@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Edwards, M H
EM: margo@soest.hawaii.edu
AF: Hawaii Institute of Geophysics and Planetology, SOEST, University of Hawai, 1680 East-West Road, Honolulu, HI 96822 United States
AU: Coakley, B J
EM: Bernard.Coakley@gi.alaska.edu
AF: Geophysical Institute, University of Alaska, 903 Koyukuk Drive, Fairbanks, AK 99775 United States
AB: The Lomonosov Ridge is a high-standing ridge of continental crust extending across the Arctic Ocean, separating the Amerasian and Eurasian Basins, and forming a continental margin to both basins. Geophysical data collected from U.S. Navy submarines during the SCICEX program shows that the Lomonosov Ridge has a different structural relationship to each of the flanking basins. These variations appear to reflect two very different types of rifting and resulting continental margins. The western Lomonosov Ridge is steep, blocky and less than 100 km wide for 450 km from the North American margin past the pole. This portion of the ridge is made up of sets of tilted fault blocks forming sediment-filled half grabens. South of 88$\deg$N on the Eurasian side, the ridge broadens to about 200 km width. The Eurasian side of the ridge remains steep and relatively straight to the Siberian slope. The majority of the broadening occurs on the Amerasian side which consists of a series of en echelon ridges oriented at about 30$\deg$ to the overall trend of the ridge. The Lomonosov Ridge is flanked on the Eurasian side by a 40-60 mGal free-water gravity low relative to the level in the Eurasian Basin, generally with a steep gradient on the basinward side of the low. The gravity gradient parallels and is located just ridgeward of the termination of the Cenozoic seafloor magnetic anomaly sequence in the Eurasian Basin and is interpreted as the ocean-continent boundary. The parallelism between the Lomonosov Ridge, the magnetic anomaly trend and the present Gakkel Ridge axis along much of the length of the Eurasian Basin implies nearly orthogonal rifting. The blocky Greenland end of the Lomonosov Ridge is paralleled on the Amerasian side by Marvin Spur, which can be traced as a narrow, linear ridge or as a gravity high across the Makarov Basin to about 88$\deg$N on the Siberian side, where the Lomonosov Ridge broadens and becomes more complex. Marvin Spur may then merge with the basinward edge of the ridge. A gravity low is situated between Marvin Spur and the Lomonosov Ridge. Further south, toward Siberia, the en echelon ridges making up the Lomonosov Ridge trend obliquely into the Amerasian Basin and die out basinward. This structure is interpreted as defining a complex sheared margin that is compatible with the rotational model for the development of the Amerasian Basin. This model predicts a pure shear margin at the Greenland end of the Lomonosov Ridge with motion becoming more oblique to the trend of the Lomonosov Ridge toward Siberia. We suggest that Marvin Spur marks the ocean-continent boundary in the shear portion of the margin and that the oblique ridges and basins at the Siberian end or the ridge consist of extended continental crust affected by trans-tensional rifting.
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
DE: 9315 Arctic region
SC: Tectonophysics [T]
MN: 2003 Fall Meeting