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The Structural Integrity of the Lomonosov Ridge with the North American and Siberian Continental Margins

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The Structural Integrity of the Lomonosov Ridge with the North American and Siberian Continental Margins The structural integrity of the Lomonosov Ridge with the North American and Siberian continental margins V. Poselov1, V. Butsenko1, A. Chernykh1, V. Glebovsky1, H. R. Jackson2, D. P. Potter2, G. Oakey2, J. Shimeld2 and C. Marcussen3 1I.S. Gramberg Research Institute for Geology and Mineral Resources of the World Ocean ‘VNIIOkeangeologia’, 1 Angliysky Ave., 190121 St. Petersburg, Russia 2Geological Survey of Canada Atlantic, Box 1006 Dartmouth, N.S., B2Y 4A2 Canada 3Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, 1350 Copenhagen K, Denmark ABSTRACT support earlier interpretations of the Lomonosov The Lomonosov Ridge crosses the Arctic Ridge as a separate microcontinent. Ocean connecting the North American and Siberian margins. The Ridge consists of a number of linear, INTRODUCTION parallel topographic highs that deepen toward the The Lomonosov Ridge, approximately 1700 km adjacent basins where they are buried by sediments. long, has a sinuous shape (Fig.1). The Ridge is named Bathymetric, seismic reflection, refraction, and after the Russian polymath Mikhail Vasilyevich Lo- potential field data show that the structure of the monosov. It was first mapped by the Russian high lat- Ridge is continuous with the adjacent continental itude air borne surveys of 1948. In 1954 it was shown margins. The sedimentary section on the Lomonosov on the bathymetric map of the Arctic Ocean (Burkan- Ridge can be traced from the North American margin ov 1954). The first bathymetric measurements on across the Pole to the Siberian margin. A reflection the Lomonosov Ridge available in western literature profile shot in the transition from the Siberian margin were made close to the pole during the First (1967) to the Lomonosov Ridge demonstrates that the strong and Second (1969) Canadian North Pole expeditions regional unconformity at the base of the hemipelagic (Weber 1983; Weber and Sweeney 1985). sedimentary unit. The entire sedimentary section The Lomonosov Ridge width varies between and the acoustic basement can be clearly followed 50 and 200 km. Its flanks rise steeply from the from the margin along the Ridge. The continuity of 3900 - 4200 m deep basins on each side to a depth sedimentary and crustal units is confirmed on the of typically 1000 - 1300 m below sea level (Weber coincident wide angle seismic reflection/refraction 1979; Bjork et al. 2007). The steep sides and the saw- profile. Magnetic data at the intersection of the Ridge toothed crest of the Ridge are typical of continental with the North American margin reveal the edge of block faulting. Seismic reflection profiles that the Pearya Terrane extending from Ellesmere Island show an angular unconformity in the sedimentary onto the Lomonosov Ridge. Furthermore, with section on the Ridge beneath the drilled Tertiary the Eurasia Basin closed the magnetic anomalies section (Jokat et al. 1992) have a distinct continental associated with Early Cretaceous dyke swarms character. The refraction velocities on the Ridge are can be traced from Franz Josef Land via the comparable with those on the Barents and Kara seas Lomonosov Ridge to the Alpha Ridge and from the shelves (Forsyth and Mair 1984), and gravity models North American polar margin to the Alpha Ridge. controlled by wide angle reflection/refraction (WAR) The distribution of the dykes suggests that since profiles (Weber and Sweeney 1985) also indicate a their emplacement the Lomonosov Ridge has been continental origin of the Ridge. In addition, the fit of stable with respect to the North American margin the Lomonosov Ridge morphological configuration and remained in close proximity to the Barents Sea with that of the conjugate Eurasia Basin margin margin until separation of the North American and suggests that the Ridge is a continental sliver Eurasian plates, as predicted by plate reconstructions separated by seafloor spreading from the Barents- based on magnetic lineations. The geomorphological Kara seas crustal block (e.g. Srivastava and Tapscott and geophysical data presented in the paper do not 1986). ICAM VI Proceedings 233 Fig. 1. Bathymetric map of the Arctic Ocean showing the location of seismic reflection lines in black and wide angle reflection/refraction lines in red described in the text. The black boxes labeled A and B are the position of the magnetic surveys shown in Figure 10. The black box labeled C is the location of gravity and magnetic surveys presented in Figure 11. The Lomonosov Ridge divides the Arctic Ocean of North America (e.g. Ostenso 1974). Another into two major deep basins (Fig. 2a): the Eurasia and transform model has the Siberian margin rifted from the Amerasia basins. It has been called a double- the Queen Elizabeth Islands with shearing along the sided continental margin (Jokat et al. 1992). The Alaska margin and Lomonosov Ridge (e.g. Herron Eurasia Basin with its two sub-basins, the Amundsen et el. 1974). The rotational model for the opening and Nansen basins (Fig. 1), was created by Cenozoic of the Amerasia Basin with Alaska rifted away sea floor spreading revealed by lineated seafloor from the Queen Elizabeth Islands margin was first spreading anomalies. This is due to the difficulties suggested by Carey (1958) and continues to be in interpreting chaotic high amplitude magnetic the option supported by the majority of researches anomalies associated with the Alpha-Mendeleev (e.g. Cochran et al. 2006). The rotational model is ridges, the weak magnetic lineations in the Canada consistent with paleomagnetic data from Alaska Basin and the scarcity of bedrock samples. Several (Halgedahl and Jarrard 1987) and restores Mesozoic different geodynamic models have been suggested geology of the Queen Elizabeth Islands with that on for the Amerasia Basin, such as rifting of Alaska the Alaskan margin (Embry 1990). The rotational from the Lomonosov Ridge requiring transform option predicts that the Amerasia Basin side of the motion along the Queen Elizabeth Islands margin Lomonosov Ridge is a sheared margin. 234 V. Poselov Fig. 2. Bathymetric map of the Arctic Ocean (section ‘a’) with the yellow line along the length the Lomonosov Ridge indicating the position of the bathymetric profile presented in section ‘b’. The black box labeled ‘c’ indicates the region of detailed bathymetric surveys. The dots on section ‘c’ are the locations of spot soundings. The north-south line with closely spaced dots is the location of the LORITA wide angle reflection/refraction profile. The orange short lines are the location of seismic reflection profiles. Significant new data collected by agencies in relative to the margins along major transform faults Canada, Denmark and Russia over the Lomonosov is required. Ridge (Fig. 1) are presented that provide information In 1992 for the first time, the Polar Marine on the continental affinities of the Ridge and its Geosurvey Expedition (PMGE) under the auspices transition to the adjacent continental margins. A of the Ministry of Natural Resources and Environ- major question addressed is whether the geophysical ment of the Russian Federation carried out WAR data can be explained by plate reconstructions observations over the Lomonosov Ridge and the ad- with the Lomonosov Ridge remaining fixed with jacent Amundsen and Podvodnikov-Makarov basins respect to the continental margins of North America (Fig. 1). In addition, aeromagnetic mapping in a belt and Siberia, or whether displacement of the Ridge 100 km wide was acquired along the WAR profile. ICAM VI Proceedings 235 In 2007, VNIIOkeanologia and the Marine Arctic m. At the 1000 m contour the plateau is about 200 Geological Expedition (MAGE) were charged by km wide. Further north the Lomonosov Ridge has the Federal Agency for Mineral Resources of the a width of about 70 km at the 1500 m contour. On Russian Federation (Rosnedra) to perform integrat- a bathymetric profile (Fig. 2b) slightly westward of ed geological and geophysical investigations on the the location of the LORITA profile, the topography Lomonosov Ridge and the adjacent Siberian Shelf. across the trough and over the plateau is not The range of scientific observations included WAR significantly different from the regional variations measurements, multichannel seismic reflection pro- observed along the length of the Lomonosov Ridge. filing and potential field (gravity and magnetic) mea- For instance, greater water depths are observed near surements in a belt 100 km wide along the WAR line. the Pole where there is an internal valley in the Ridge The Geological Surveys of Canada (GSC) and or towards the Siberian margin (at about 700 km on Denmark and Greenland (GEUS) acquired WAR figure 2b) where one limb of the sub-parallel ridges data and limited reflection profiling over the junction that form the Lomonosov Ridge is crossed. of the Lomonosov Ridge with the Greenland and The transition from the Siberian margin to the Ellesmere Island continental margin in 2006. In 2007 Lomonosov Ridge (Fig. 1 and 2) is smooth for the and 2009 on LOMROG I and II ship-based programs, first 200 km from the shelf. The water depth increases seismic reflection profiles on the Lomonosov Ridge steadily from about 200 m to 1750 m over about 200 were collected by GEUS that are also shown here. km. Further northward the Lomonosov Ridge is In this paper the Lomonosov Ridge will be made up of a complex of ridges and basins as seen described from the continental shelves towards the in the rugged topography. A consistent feature of this North Pole through successive data sets beginning region of the Lomonosov Ridge is a series of parallel with bathymetry and continuing with data that ridges with a width of over 200 km extending south to investigate the sedimentary and crustal structure. at least 82°30’ N and, based on gravity data, perhaps to the Siberian Margin (Cochran et al. 2006). BATHYMETRY The contours on the International Bathymetric SEISMIC REFLECTION DATA Chart of the Arctic Ocean (IBCAO version 2.0) Near the North American margin (Jakobsson et al.
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