ARCTIC PALEOGEOGRAPHY AND PLATE TECTONIC EVOLUTION OF THE AMERASIAN BASIN

MILLER, Elizabeth L., Geological and Environmental Sciences, Stanford University, Stanford, CA 94305, [email protected], TORO, Jaime, Depart. of Geology & Geography, West Virginia Univ, 425 White Hall, Morgantown, WV 26506, and GEHRELS, George, Department of Geosciences, University of Arizona, Tucson, AZ 85721

U-Pb ages of detrital zircon suites from Triassic sandstones from the circum-Arctic region can be used to help evaluate plate tectonic models for the origin of the Amerasian Basin of the Arctic Ocean. The current most popular plate tectonic model involves rifting and counter-clockwise rotation of the Arctic Alaska-Chukotka microplate away from the Canadian Arctic margin to its present position. Although this satisfies many stratigraphic and geophysical constraints for the Alaska part of the reconstruction, it restores Chukotka and Wrangel Island to a position adjacent to the Canadian Arctic, which is at odds with existing detrital zircon age data. Northward-derived Triassic sandstones of the Sverdrup Basin, Arctic Canada (characterized by 500-600 Ma and 445-490 Ma zircons) have sources that are distinct from sources that fed the Triassic basinal turbidite sequences of Chukotka and Wrangel Island (characterized by 235-265, 280-330, 340-390, 420-580 and 1000-1300 Ma zircons). The Triassic of Chukotka and Wrangel Island likely occupied an initial pre-rift location near source areas in Siberia, the Taimyr and/or the Polar Urals and are similar to detrital zircon suites of the northern Verkhoyansk fold and thrust belt. Permo-Triassic zircons in Chukotka and Wrangel samples may indicate derivation from the general region of the Siberian Traps or the Taimyr. A revised paleogeographic reconstruction of the Arctic places the Chukotka part of the Arctic Alaska plate closer to Russia and northern Alaska against Arctic Canada. Implications of this new reconstruction suggest a rift origin of the Makarov Basin (opening perpendicular to the Lomonosov Ridge), strike-slip motion along the South Anyui suture, significant internal deformation of Chukotka and the offshore Siberian Shelf, and a possibly slightly younger rotation of Arctic Alaska. Formation of the Amerasian Basin may have been localized by hotspot magmatism in the mid-Cretaceous but was ultimately driven by subduction-zone rollback towards the Pacific.