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John Brozena, Naval Research Laboratory (United States)
Lawrence Lawver, University of Texas Institute for Geophysics (United States)
Vicki Childers, Naval Research Laboratory (United States)
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In 1955, Carey first suggested a rotational opening of the Arctic Ocean based on his theories concerning oroclinal bending. Grantz in 1966, Hamilton in 1967 and Tailleur in 1969 formulated the idea that the Canada Basin may have opened about a pivot point in the Mackenzie Delta. The Arctic Ocean can be divided into a mostly Tertiary to present Eurasian Basin, and the older Mesozoic Amerasian Basin. Even with additional data from the Amerasian Basin including extensive airborne, ship-based, and satellite magnetics and gravity, the tectonic evolution of the Canada and Makarov components of the Amerasian Basin are still controversial. While the final phase of opening of the Amerasian Basin may have been rotational about a pivot point near or south of the Mackenzie Delta, the earlier phases and even the directions of the initial basin formation are still controversial. Vogt and others first suggested a possible hotspot origin for the Alpha and Mendeleev Ridges and related them to the Iceland hotspot. Age versus depth and heat flow versus depth give a tentative age for the Amerasian Basin of latest Jurassic to early Cretaceous with seafloor spreading ending prior to the beginning of the Cretaceous Normal Superchron around 120 Ma.
To complement and extend the early US Navy Arctic aeromagnetic surveys of the 1970's and 80's, the Naval Research Laboratory conducted three field seasons of modern aerogeophysical (gravity and magnetic) Investigations over the Amerasia Basin. Tracks were run obliquely to the older data at typical line spacings of 18 km which densified and allowed cross-over adjustment, gridding and contour presentation of the magnetic data. This, coupled with the new airborne gravity data, allows Insights Into the tectonic development of the region. From our results, we see a three or more stage opening of the Amerasian Basin. The first stage involved rifting of the Arctic Alaska/Chukokta block from the Canadian Arctic Islands. As this first stage rifting evolved, the Chukchi Borderland/Northwind Ridge complex rotated out of the North Chukchi Basin, similar to present motion in the Afar region with rotation of the Danakil block. The first stage was followed by a reorganization and a final stage that produced rotational opening about a pole northeast of Fairbanks, AK. Our final stage pole of rotation, 66N 138.5W, is supported by the aeromagnetic data collected by Sergei Maschenkov and others in the Makarov Basin. The Northwind Ridge was originally along the Sverdrup Basin margin of Canada. Timing of the stages is inexact due to a lack of correlatable magnetics but in schematic, we interpret the evolution of the region as: extension commenced by ∼150 Ma; rotation of the Chukchi Borderlands began by ∼135 Ma; and the final stage of opening of Amerasian basin ceased by the beginning of the Cretaceous Superchron (120-118 Ma) because the gravity anomaly that marks the abandoned spreading center in the Canada Basin is flanked by magnetic anomalies.
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