ARCTIC PALEOGEOGRAPHY AND TECTONICS: IMPLICATIONS FOR CORDILLERAN TERRANES

Years of data acquisition in the Arctic, primarily focused on its pre-Cretaceous reconstruction, reveal aspects of Arctic paleogeography during the Paleozoic and Mesozoic that are relevant for Cordilleran tectonics. Basement ages together with more than 60 detrital zircon age distributions from fossil-dated Paleozoic and Mesozoic strata confirm that Arctic Alaska, NE Russia and parts of adjacent shelves share common basement ages and a stratigraphic history that place them close to the Barents Shelf prior to opening of the Amerasian Basin.

The Caledonian orogeny stitched Baltica and Laurentia together during the Silurian to Early Devonian, a suture that extends north across the Arctic. These two cratons remained linked until the opening of the Atlantic, but their suture was truncated by Late Devonian-Early Mississipian rifting across what is now the Alaska. Rift basins and extension (?) related magmatism at ~ 380-390 Ma mark this event. The truncated margin was partly underlain by crust of Baltica affinity, including the 750-550 Ma Timanides as well as by the Caledonides- represented in Alaska by an Early Devonian deformational belt. Stable platform carbonate deposition lasting ~ 80 Ma characterized the (now) Arctic portion of the paleo-Pacific margin from the Carboniferous to the Permian. Clastic detritus in this sequence was derived from the erosion of the Baltic Shield (abundant 1-2 Ga detrital zircons) as well as the Timanide and/or Caledonian orogens (represented by ~ 550-750 and 400-490 Ma zircons). North American sources are represented along the Laurentian part of the margin.

Late Devonian and Early Mississippian rifting significantly restructured Laurentian paleogeography by extending the older passive margin of western Laurentia along the (now) south-facing, younger margin of Arctic Alaska. Rift fragments bearing Caledonian Ordovician-Devonian magmatic rocks that formed atop Timanide basement and/or adjacent to Baltica may have been displaced southward along the Cordilleran margin of Laurentia during this rifting (i.e., Alexander, Klamath and N. Sierra terranes). Comparison of Arctic detrital zircon populations with those from “Baltic” affinity terranes in the Cordillera reveal remarkable similarities that are most likely explained by the above described series of events in the Arctic.