PALEOGEOGRAPHY AND BASIN DEVELOPMENT IN THE CIRCUM-ARCTIC REGION: SINGLE-GRAIN U-PB DATING OF DETRITAL ZIRCON POPULATIONS FROM TRIASSIC SANDSTONES IN NE RUSSIA AND COMPARISON TO ALASKA AND CANADA

In order to test and explore alternatives to existing models for the formation of the Amerasian Basin of the Arctic, detrital zircon suites from 12 samples of Triassic sandstone from the Circum Arctic region (100 grains each) were dated by LA-ICPMS.

The Triassic represents the last major phase of deposition in the Arctic region prior to the onset of Jurassic deformation and the beginning of Cretaceous rifting and sea-floor spreading which formed the Amerasian Basin and disrupted the original paleogeography of the region. The samples dated provide key evidence for the reconstruction of continental fragments dispersed during this rifting.

Samples from the Verkhoyansk thrust belt of Eastern Siberia are characterized by strong Permo-Carboniferous (280-320 Ma), and Cambro-Ordovician (439-540 Ma) peaks in the cumulative probability plots. These match ages of granitoid batholiths in the Baikal Mountains along the southern edge of the North Asia craton, and suggest that the immense Carboniferous-Jurassic passive margin sedimentary prism of the Verkhoyansk margin was sourced from the Baikal region with sediments transported by a major river system flowing along the Vilyui rift graben.

Samples from Chukotka, NE Arctic Russia, also show Permo-Carboniferous peaks, as well as younger Permo-Triassic peaks (about 250 Ma). The younger zircons could be derived from silicic magmas erupted during the outpouring of basalt related to Siberian Trap LIP volcanism. Triassic sandstones from Wrangel Island and westernmost Alaska (Lisburne Hills) share both of these zircon age peaks. Samples from further east in Alaska and Canada (Saddlerochit Mountains and Sverdrup Basin) do not.

The current most popular reconstruction of the Arctic Amerasian Basin involves counter-clockwise rotation of Arctic Alaska and Chukotka away from the Canadian Arctic margin. Although this satisfies many constraints for the Alaska portion of the reconstruction, it places Chukotka a great distance away from Siberia, with which is more clearly linked depositionally based on both stratigraphic and detrital zircon data. This discrepancy supports alternative models that involve right-lateral slip of Chukotka from the northern Verkhoyansk along the South Anyui suture and a more complex model for the internal deformation of this part of the Arctic Alaska-Chukotka microplate.