The Lomonosov Ridge experiment: 'Lorex 79'

Abstract

In the spring of 1979 the Department of Energy, Mines and Resources (EMR) undertook a large‐scale, multidisciplinary project to study the nature and origin of the Lomonosov Ridge. The scientific program was planned and coordinated by the Earth Physics Branch, and the logistic support was provided by the Polar Continental Shelf Project/Scientists from other branches of EMR, from the Department of Fisheries and Oceans (DFO), and from a number of universities in Canada and the U.S.A. took part in the project code named Lorex 79. The Lomonosov Ridge is an aseismic submarine mountain range that bisects the Arctic Ocean into the Amerasia and Eurasia Basins (Figure 1). It rises sharply to a height of some 3 km above the adjacent abyssal plains, the Makarov Basin to the west, and the Fram Basin to the east. It is close to 200 km wide where it approaches the North American and Eurasian continental shelves but narrows to 25 km at its midpoint near the North Pole. Its relatively flat top, the steepness of its flanks, and results from previous geophysical measurements indicate that it may be a sedimentary structure of continental origin rather than a structure of oceanic origin [Sweeney et al., 1978]. In this context it has been suggested on several occasions that it is a rafted fragment split off the Eurasian continental shelf at the time of the opening of the North Atlantic and the Eurasia Basin in Early Tertiary times. However, since the available geophysical, geological, and bathymetric data are relatively sparse and often of doubtful quality (because of the enormously difficult operating conditions), the continental nature of the Lomonosov Ridge has never been unambiguously demonstrated.

Mid‐Cenozoic tectonic and paleoenvironmental setting of the central Arctic Ocean

“…A single seismic refraction profile collected from a drifting ice island during the Canadian Lomonosov Ridge Experiment (LOREX) in 1979 [ Weber , 1979] (Figure 3) provides one of the few constraints on the deeper crustal structure of the central LR. In close proximity to the ACEX drill sites, the upper crust has a thickness of 5 km and a velocity of 4.7–5.2 km/s, and the lower crust exceeds 20 km thick with a velocity of 6.6 km/s [ Mair and Forsyth , 1982; Forsyth and Mair , 1984].…”

Peculiarities of roughness and thickness of oceanic crust in the Eurasian Basin, Arctic Ocean

“…A low‐density zone of 3200 kg m −3 for the upper mantle is introduced below the central part of the ridge to model the strong negative gravity anomaly. Additional constraints on the thickness and structure of the oceanic crust were derived from results of seismic refraction investigations during the LOREX and FRAM expeditions (Weber 1979; Jackson et al . 1982; Kristoffersen et al.…”

“…(1995a,b). The stars show thickness values based on observations of the LOREX expedition after Weber (1979) for the northern Amundsen Basin (reference e), and from the FRAM‐II expedition after Duckworth & Baggeroer (1985) for the Amundsen Basin (reference f).…”

“…The only seismic control on the Moho depth of the Amundsen Basin is that available from the LOREX Expedition close to the Lomonosov Ridge (Weber 1979; Mair & Forsyth 1982). A depth of 12 km for the Moho about 80 km away from line 2 (Fig.…”

“…(1982); (line c) from Jackson et al . (1984); (line d) from Duckworth & Baggeroer (1985); (line e) from Weber (1979); and (line f) from Duckworth & Baggeroer (1985). (b) Pattern of the magnetic anomalies and the Chron numbers for the Amundsen and Nansen basins (modified after Kovacs et al .…”