BALTICA IN THE CORDILLERA?

U-Pb ages of detrital zircon suites from Paleozoic strata in Arctic Alaska-Arctic Russia and the Alexander, northern Sierra Nevada and Klamath Mountain terranes of the Cordillera suggest an exotic Gondwana or Baltic origin for these terranes. We test these hypotheses with U-Pb ages obtained on detrital zircon suites from Cambrian to Devonian strata that overlie Precambrian rocks of the northern Baltic Shield. Seven samples were analyzed from two stratigraphic sections, one along the western flank of the Polar Urals (Ordovician and Devonian quartzite and sandstone) and the other near Saint Petersburg (Cambrian, Ordovician and Devonian sandstone). The Ural section overlies Neoproterozoic rocks deformed and accreted in the early Cambrian Timanide orogeny and the St. Petersburg section overlies older Precambrian rocks of the Baltic Shield. All samples contain at least some Precambrian Baltic Shield zircons ( greater than 1 Ga), variable amounts of Neoproterozoic-Cambrian zircons (~ 490 - 800 Ma) and only rare younger grains. The two Devonian samples have the least amount of Neoproterozoic zircons and the most older Precambrian zircons. In comparing these data to similar data from the allochthonous terranes of the Cordillera, our results indicate that the Precambrian zircon populations (~ .8- 3 Ga) in northern Baltica strata compare well with similar age detritus in the Cordilleran terranes, but that the percentage and age of younger components are more variable. Paleozoic strata of Arctic Alaska-Arctic Russia are most similar to Baltica based on both their lithostratigraphy and detrital zircon populations, in strong support of continental reconstructions that place Arctic Alaska-Arctic Russia near the Barents Shelf of Russia- to the east, not west, of the Caledonides. This reconstruction, which is also supported by previously published detrital zircon data on younger rocks, opens the possibility that the along-strike continuation of the Cordilleran margin during part of the Paleozoic might have been the eastern (Uralian) margin of Baltica.