Tectonics of the Western Amerasian Basin

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Source www.۳۳igc.org
Holding Date 18 August 2008
Tectonics of the Western Amerasian Basin
Kosko, Mikhail; Grikurov, Garrik; Kaban\'kov, Vasily; Poselov, Victor
VNIIOkeangeologia, Russian Federation

The eastern part of Amerasian Basin is occupied by deep Canada Basin, while the western part demonstrates complex bottom topography defined by contrasting negative and positive morphostructural forms. Among the latter the most prominent are Lomonosov Ridge, Alpha Ridge, Mendeleev Rise, Arlis Plateau, Chukchi Cap and Northwind Ridge. Together with intervening Makarov Basin and some smaller depressions this entire morphostructural ensemble represents, in fact, an over-deepened shelf which bridges the North American and Asian continents and is interpreted as part of the submerged Hyperborean Platform.
The concept is consistent with available geological, seismic and potential field data. Of special importance are the results of bottom sampling which provided numerous large-sized fragments of predominantly sedimentary rocks. The clasts are particularly abundant on tops and steep slopes of bathymetric highs but rapidly wane out toward deeper seabed. Such distribution suggests the derivation of debris from local bedrock sources draped by only thin veneer of loose sediments. The main dredged lithologies include clastic and carbonate rocks of inferred late Precambrian age, fossiliferous Paleozoic carbonates with associated sandstones and Mesozoic clastics and are believed to represent continental platform cover sequences on ancient cratonic basement.
Deep seismic sounding experiments confirm the similarity of crustal structure beneath Lomonosov Ridge and Mendeleev Rise both of which display the presence of moderately thinned upper crustal layer continuously traced from the adjoining parts of the Siberian continental shelf. Stronger thinning or even local rupturing of the upper crust is observed under the deepest bathymetric lows.
The presented data favor a continental nature of the western Amerasian Basin which appears to have formed by extensional fragmentation (rifting) and subsidence of a Precambrian platform area possibly partly intersected and/or rimmed by younger fold belts. The proposed interpretation severely constrains geodynamic models implying a purely volcanic origin of the Alpha-Mendeleev system within a rotational oceanic opening between the Canadian and Alaska-Chukotka plates.