THE ROLE OF CHUKOTKA DURING OPENING OF THE AMERASIAN BASIN: A NEW PALEOGEOGRAPHIC MODEL FOR THE ARCTIC DURING THE MESOZOIC

The most widely accepted model for the opening of the Amerasian Basin of the Arctic proposes that Arctic Alaska rifted from the Canadian Arctic margin and rotated anti-clockwise to its present position about an Euler pole located in the Mackenzie Delta area of Canada (e.g., Grantz et al., 1979). Persuasive geological and geophysical data support the Arctic Alaska-Canada connection, but the role of Chukotka (NE Russia) remains problematic. Many workers consider NE Arctic Russia to be part of the Arctic Alaska-Chukotka Microplate (AACM), which was displaced during Arctic opening. However, rotating the entire AACM back to the Canadian Arctic creates a severe overlap of continental crust. This overlap is made worse by the existence of several submerged blocks of continental crust that also must be restored (Chukchi Cap and Northwind Ridge). Some have dealt with the overlap of continental crust by including in the AACM only the part of Chukotka that is adjacent to Alaska. However, this is not supported by the geology of Chukotka. Another model requires internal deformation of the AACM and a double-hinge geometry, with Chukotka rotated clockwise about a pole in the lower Lena region of Russia while Arctic Alaska rotates anti-clockwise (Miller et al., 2006; Kuzmichev, 2008). The problem with this model is that it conflicts with the history of accretion of displaced terranes along the Verkhoyansk margin of NE Russia and it requires improbably complicated kinematics for the Amerasia Basin. Here we propose an alternative model, developed using the GPlates software, in which Chukotka remains attached to Siberia in approximately its current position and only joins Arctic Alaska after the Canada Basin is open. Advantages of this model are: 1) it avoids overlap of continental crust; 2) it has relatively simple kinematics for the movements of Arctic Alaska; 3) it allows for the accretion of the terranes of NE Russia; and 4) it honors the provenance links for Triassic and Jurassic deposits of Chukotka and Alaska. One element that has been previously used to justify the unity of the AACM is the correlation of the Angayucham ophiolites of Alaska with the South Anyui zone of Chukotka. In our model, these are two convergent margins that face two separate sub-basins of the paleo-Pacific realm.