SIBERIAN CONNECTION OF PRECAMBRIAN THROUGH TRIASSIC ROCKS OF ARCTIC ALASKA

CLOUGH, James G., Alaska Div. of Geological & Geophysical Surveys, 3354 College Road, Fairbanks, AK 99709-3707, [email protected] and BLODGETT, Robert B., U.S. Geological Survey - Contractor, 4200 University Drive, Anchorage, AK 99508

The tectonic model for opening of the Canada Basin by counterclockwise rotation of the Arctic Alaska Plate (AAP) from the Canadian Arctic Islands is not supported by paleobiogeographic and sedimentologic evidence collected from Precambrian- through Triassic-age rocks of Arctic Alaska. We favor a model that involves rifting of the AAP from Siberia beginning in Early Cretaceous time, possibly along a sinistral transform system adjacent to the Canadian Arctic Islands.

Paleobiogeographic affinities of the AAP suggest that it was probably derived as a rift block from the Siberian paleocontinent, rather than from Laurentia (Canada Basin). Strong paleobiogeographic affinities of Late Ordovician (Ashgillian) faunas in the Nanook Limestone (northeast Brooks Range) indicate that the easternmost AAP was closely associated with Siberia (Kolyma and Taimyr) and holds little connection to the North American craton. Further evidence for affinities to Siberia (as well as Eurasia) is noted among Cambrian trilobites, Ordovician conodonts, Mississippian brachiopods (gigantoproductids in upper part of the Alapah Limestone) and plants, as well as by Late Triassic brachiopods from the Otuk Formation.

Paleocurrent directions for the Neoproterozoic Katakturuk Dolomite (northeast Brooks Range) and the similar-age Shaler Supergroup in the adjacent Victoria Island and Amundsen Basin are in ~100 degree opposition for a rotational-restored Arctic Alaska plate. When the Arctic Alaska plate is restored in the rotational model, Upper Devonian clastics of northern Alaska are in 180 degree opposition to coeval units in the Canadian Arctic Islands.

A Late Proterozoic rifting event at ~780 Ma (recorded in the lower Katakturuk Dolomite) created a thermally subsiding passive margin that existed for nearly 400 million years of predominantly carbonate deposition. The AAP remained attached to Siberia through at least Middle Devonian time. Initial breakup of the AAP from Siberia occurred in the mid-Early Cretaceous, possibly followed by sinistral translation along a transform fault adjacent to the Canadian Arctic Islands. Collision of the AAP with terranes situated to the south (Angayucham and other terranes) during the Mesozoic resulted in compressional tectonics that formed the Brooks Range orogenic belt.