U-Pb and oxygen isotope characteristics of Timanian- and Caledonian-age detrital zircons from the Brooks Range, Arctic Alaska, USA

The Devonian connection between the Brooks Range of Alaska, USA, with the continental margin of Arctic Canada and its subsequent Jurassic-Cretaceous counterclockwise rotation to form the Amerasian Basin, is a highly debated topic in Arctic tectonics. This resource-rich region was assembled from terranes that formed part of Laurentia or Baltica, or were juvenile oceanic arcs in the early Paleozoic that were brought together during Caledonian Orogenesis and the subsequent collision that formed Pangea (Uralide Orogeny). Elements of these orogens, as well as older ones, are predicted to occur in the Brooks Range of Arctic Alaska. This study presents the first combined zircon U-Pb and oxygen data from six Brooks Range metasedimentary units with assumed Neoproterozoic to Devonian ages. Three distinct detrital zircon patterns are identified in these units: (1) those with Neoproterozoic maximum depositional ages characteristic of the Timanide Orogen of northern Baltica and adjacent parts of Siberia, (2) an almost unimodal Siluro-Ordovician (443.5 +/- 2.3 Ma) detrital zircon population consistent with the oceanic Apoon arc believed to have existed off shore of northern Laurentia and to have accreted to the North Slope subterrane during the Caledonian event, and (3) those with Middle Devonian maximum depositional ages consistent with postaccretion extension during the final (Scandian) phase of Caledonian Orogenesis. Oxygen isotopes from the same zircons reveal minor to significant crustal contamination with approximately two thirds (n = 255/405) having delta O-18 values >5.9 parts per thousand (above the mantle field of 5.3 +/- 0.6 parts per thousand). Pattern 1 units exhibit a progressive increase in delta O-18 values throughout the Proterozoic (5.99 to 9.29 parts per thousand indicative of increasing crustal growth and Timanide age zircons yield average delta O-18 values of 7.18 +/- 0.64 parts per thousand (n = 26) suggestive of more crustal influence than Caledonian age zircons, possibly reflecting northern Baltica signatures. The unimodal population in Pattern 2 yields average delta O-18 values of 5.49 +/- 0.66 parts per thousand (n = 17) and 6.02 +/- 0.27 parts per thousand (n = 23) prior to and during, respectively, the main Caledonian event and suggest derivation from Devonian juvenile arc sources possibly representing the initiation of the collision between Laurentia and Baltica. Similar to Pattern 1, the delta O-18 values associated with Pattern 3 show a progressive increase in delta O-18 values throughout the Proterozoic (5.00 to 9.39 parts per thousand. However, Pattern 3 also exhibits a distinct juvenile fingerprint (6.13 +/- 0.24 parts per thousand, n = 51) during the main Caledonian event and a slight increase to 7.12 +/- 1 parts per thousand (n = 7) in post-Caledonian zircons possibly suggest correlating with a postaccretion phase in which proximally sourced zircon-bearing detritus was deposited in extension-related basins marking the joining of Laurentia and Baltica.