International Geologiical Congress - Oslo 2008

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AAA-01 Paleogeographic evolution of the Arctic region during the Phanerozoic - Part 1

 

Tectonic development of the Amerasia Basin, Arctic Ocean

 

Arthur Grantz, Consulting Geologist (United States)
Patrick E. Hart, U.S. Geological Survey (United States)
 

 

Seismic reflection, refraction and potential field data from Amerasia Basin in conjunction with piston cores from Northwind Ridge suggest that the basin was formed by four rotational extensions. The first event stretched and thinned Pangea on a westerly-dipping crustal scale detachment fault system of Sinemurian to no later than Early Hauterivian age that day-lighted on the east along the continental margin of Northwestern Canada. This event rotated Eastern Siberia about 50° anticlockwise from Northwest Canada about a pole in the lower Mackenzie Valley and created transitional crust lacking seafloor spreading magnetic anomalies beneath the margins of the Amerasia Basin.
The second event, 9° or 10° of anticlockwise rotational seafloor spreading, split the earlier-formed transitional crust and emplaced MORB (mid-ocean-ridge basalt) along a northerly trending symmetry axis in the center of the Amerasia Basin. The resultant fan of magnetic anomalies, estimated to be of Late Hauterivian to Late Barremian age (136-125 Ma), is geometrically symmetrical with the first spreading event and likewise converges toward a pole of rotation in the lower Mackenzie Valley.
Approximately 35° of clockwise rotation of Chukchi Microplate out of the East Siberian shelf about a pole near 72.5° N, 170° W constitutes the third rotational event, which probably occurred during or shortly following the Late Barremian. This event thrust the northeastern corner of the Chukchi Microplate across the boundary between event 1 and event 2 crusts in the western Canada Basin and created North Chukchi Basin in its wake. North Chukchi Basin is partially filled with post-Barremian to Early Campanian oceanic basalts of the Alpha-Mendeleev Large Igneous Province (125-80 Ma). In the absence of well-defined aeromagnetic anomalies or crustal-scale reflection data we can only speculate, on the basis of morphology, that North Chukchi Basin is a product of localized rotational seafloor spreading.
The fourth event, mildly rotational Paleocene extension, created basin and range structural morphology and the northerly-trending Northwind Basin in the axial region of the Chukchi Microplate. This extension thinned the continental crust of the microplate beneath the Northwind Basin by about 35 percent and created accommodation space for >2,000 m of water and >4,500 m of clastic sediment within the basin. The pole of this rotation was apparently located on the central Chukchi shelf.
Following the four extensional events the southeastern margin of the Amerasia Basin was subject to far-field convergence of Middle Eocene to Quaternary age that appears to have originated at the Pacific Rim and created large thrust-related detachment folds in the southeast Amerasia Basin that may be significant for hydrocarbon exploration.

 

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