Mesozoic magnetic lineations in the Bering Sea Marginal Basin

Abstract

A compilation of marine magnetic profiles from the Bering Sea marginal basin has revealed the existence of north‐south trending magnetic lineations over the deep abyssal basins. The anomalies in the Aleutian and Bowers basins have maximum peak to peak amplitudes of 350 γ and wavelengths characteristic of sea floor spreading anomalies (25–100 km). These lineations are as much as 600 km long. In contrast, linear trends within the Komandorsky Basin are less distinct and have anomalies with variable amplitudes. The magnetic anomalies along an 850‐km profile crossing the Aleutian Basin have been correlated with the M1‐M13 (117–132 m.y.) sequence of Larson's (1974) Mesozoic time scale. These anomalies increase in age from east to west and yield a half spreading rate of 5.1 cm/yr. North‐south trending anomalies within Bowers Basin exhibit shapes and spacings similar to those from the Aleutian Basin, suggesting that these trends may have been connected at one time. Detailed model studies of the anomalies in the Aleutian Basin yield results which support the hypothesis that the igneous crust in the eastern Bering Sea is trapped oceanic plate which may have been part of the Mesozoic Pacific Basin. The model studies have indicated that (1) normalized magnetization intensities are comparable to those estimated for the Mesozoic Hawaiian Lineations in the Pacific, (2) the approximate phase angle of the observed anomalies (−10°±20°) would allow the magnetic lineations either to be formed at their present location or else to be formed at a more southerly site and then moved to their present location, and (3) the width of transitions between adjacent polarity intervals is relatively large (W ≥ 16 km) and may be related to a redistribution of the remanent magnetization within a deeply buried layer 2. The corrected depth to layer 2 is within 5% of the depth predicted for Mesozoic crust (120 m.y.) on the Sclater (1972) depth versus age curves. Although the north‐south trending anomalies in the Aleutian and Bowers basins are interpreted as sea floor spreading anomalies, the origin of the anomaly pattern in the Komandorsky Basin is not understood.

Aleutian basin oceanic crust

“…The original hypothesis for the nature of Aleutian basin crust was Mesozoic oceanic crust, trapped when subduction moved ∼55-50 Ma from the Beringian margin to its current location at the Aleutian ridge [Scholl et al, 1975;Cooper et al, 1976bCooper et al, , 1987Worrall, 1991;Cooper et al, 1992]. However, later magnetic analyses suggested a change in lineation orientation at the Vitus arch ( Fig.…”

“…In contrast, the Aleutian basin ( Fig. 1) is commonly modeled as oceanic crust, trapped ∼55-50 Ma when subduction moved from the Beringian margin to its current location beneath the Aleutian ridge [Scholl et al, 1975;Cooper et al, 1976bCooper et al, , 1987Worrall, 1991;Cooper et al, 1992]. Little is known about the deep structure of the Aleutian basin, except that early seismic refraction profiles suggest a velocity structure consistent with oceanic crust [Shor, 1964;Ludwig et al, 1971;Cooper et al, 1979].…”

“…The primary hypothesis for Aleutian basin formation is that it is underlain by Mesozoic oceanic crust [Scholl et al, 1975;Cooper et al, 1976bCooper et al, , 1987Worrall, 1991;Cooper et al, 1992]. Fig.…”

Structure and Quaternary tectonic history of the Woodlark triple junction region, Solomon Islands

“…In addition, the Ayu Trough is being subducted endon beneath the western New Guinea Trench (Taylor and Karner, 1983), but the data available for this region (Milsom et al, 1992) do not resolve the intersection geometry. Seafloor magnetic data show that, during the Tertiary, collisions between spreading ridges and trenches occurred at the Antarctic Peninsula (Barker, 1982), the South Scotia Ridge (Barker et al, 1984), the Aleutian Trench (Cooper et aL, 1976;Marshak and Karig, 1977;DeLong et al, 1978) and the Shikoku margin (Hibbard and Karig, 1990a, b).…”

Geology of the Komandorsky Deep Basin

“…Structural-tectonic scheme of the Bering Sea region (according to BOGDANOV and NEPROCHNOV, 1984). 1, Areas of the Mesozoic fold zone and pre-Albian accretion prism; 2, pre-Albian oceanic plate; 3, pre-Middle Miocene oceanic plate; 4, active volcanoes; 5, extinct volcanoes; 6, epicenters of earthquakes; 7, subduction zones; 8, axis of spreading; 9, thickness of sediments on the Aleutian plate and on the edge of the shelf (isolines in 2 km); 10, magnetic anomalies in the Bering Sea (according to COOPER et al, 1976); 11, magnetic anomalies on the Pacific plate. by a young spreading origin of the acoustic basement.…”