A SYNTHESIS OF DETRITAL ZIRCON DATA ACROSS 250 KM OF THE CENTRAL AND SCHIST BELTS OF THE BROOKS RANGE, ALASKA: IMPLICATIONS FOR ARCTIC TECTONIC SUTURES

The provenance and tectonic affinity of the metasedimentary and metaigneous rocks making up parts of the Brooks Range, Alaska, can help constrain the pre-rifting configuration of the Amerasian basin, Arctic Ocean. Rocks now entrained in the Brooks Range may preserve remnants of their pre-rift configuration and earlier tectonic events, i.e.- the Caledonian and/or Timanian suture(s). Zircon U-Pb ages from Brooks Range metasedimentary rocks are used to determine sediment provenance and suggest tectonic linkages across the Arctic region.

The Brooks Range is a fold-and-thrust belt striking parallel to the Alaska Arctic margin and is cut by rivers flowing perpendicular to orogenic strike. Joint Swedish-American expeditions down four Alaskan rivers (North Fork of the Koyukuk, John, Alatna, and Ambler) allowed us to sample units across 250 km of strike. Results from the John River have been published (Hoiland et al., 2017), while results from the North Koyukuk are presented in a companion poster and in Robinson et al. (2019). We present the Alatna river results in this poster.

The five units sampled along the Alatna River include the Devonian Hunt Fork shale (Dhf?), Devonian Skajit limestone (Dssk), Paleozoic (?) wacke and limestone (Pzus), Paleozoic (?) undifferentiated schist (Pzmsu), and Paleozoic (?) quartz mica schist (Pzqms). The samples define two groups: Group 1 (the majority of our samples) has a Tonian maximum age of deposition (MAD) and significant Mesoproterozic (c. 900-1800 Ma) consistent with derivation from Baltica; Group 2 (Dhf?, Pzus) has Carboniferous (330 Ma, 300 Ma) MADs, younger than their supposed stratigraphic ages, with abundant Devonian and Neoproterozoic detritus - because the MADs are younger than the accretion of the southern Brooks Range terrane(s) to the northern margin of Laurentia, Group 2 is a post-accretion assemblage with detritus from Laurentia ± Caledonian orogen ± accreted terranes.

Results from the three rivers are remarkably similar and identify distinct provenance signatures that broadly correlate with Devonian (Caledonian) versus Neoproterozoic (Baltican) input at a regional scale. We link these signatures to the Paleozoic Caledonian suture between Laurentia and Baltica that was later disrupted by Brookian folding and faulting.