PALEOGEOGRAPHIC RECONSTRUCTION OF THE ARCTIC ALASKA-CHUKOTKA TERRANE BASED ON ZIRCON AND PALEONTOLOGIC DATA FROM SEWARD PENINSULA

The Arctic Alaska-Chukotka terrane (AAC) is a Neoproterozoic to early Paleozoic continental fragment that accreted to northwest Laurentia sometime during the Paleozoic. Combined geologic, detrital zircon, and paleontologic data from Seward Peninsula—one part of the terrane—restrict options for paleogeographic reconstructions.

Seward Peninsula (SP) is underlain by relicts of Neoproterozoic crystalline basement and a latest Neoproterozoic to Middle Devonian carbonate platform; the platform is overlain by Devonian or younger siliciclastic rocks.

An incipient rift formed within the platform sequence between the latest Neoproterozoic and Middle Devonian, probably during the Ordovician. Rift deposits contain detrital zircons dominated by 700-570 Ma ages. Younger siliciclastic rocks contain dominant populations at 440-420 Ma and lack the Neoproterozoic populations that characterize the rift deposits.

Basement ages from SP (Amato et al., 2009) overlap with those of detrital zircons from the rift deposits and with igneous and detrital zircon ages from parts of the Uralian orogen (Polar Urals, Novaya Zemlya, Taimyr) that are thought to represent the Timanide margin of Baltica (Pease and Scott, 2009). Early Ordovician trilobites from SP are most like those in Novaya Zemlya; Late Ordovician trilobites are similar to those in Taimyr, the Siberian platform, and several peri-Siberian terranes. Ordovician conodont assemblages from the SP contain both Laurentian and Siberian endemic forms. The rift basin on SP likely formed on the margin of Baltica during the Ordovician opening of the Uralian ocean; the AAC was close to Siberia and Laurentia in Late Ordovician time.

The 440-420 Ma detrital zircon population in the siliciclastic rocks of SP is known in other parts of the AAC (e.g., Brooks Range) and parts of northwest Laurentia (Gehrels and Howell, 1999; Lemieux et al., in press). The depositional age of rocks that contain the population, where known, is Devonian. By Late Devonian, the AAC was adjacent to northwest Laurentia and both were receiving a significant supply of 440-420 Ma zircons.

Movement of the AAC from its “birth” in the vicinity of the Uralian ocean to a position adjacent to northwest Laurentia may have occurred by processes similar to the Northwest Passage model of Colpron and Nelson (2009).