U-PB ANALYSIS OF DETRITAL ZIRCONS FROM MESOZOIC STRATA IN THE NORTHERN TALKEETNA MOUNTAINS, SOUTH-CENTRAL ALASKA

The Alaska Range suture zone is defined by a transition from outboard oceanic terranes to inboard continental margin terranes in south-central Alaska. The three fundamental geologic features of the Alaska Range suture zone include the accreted oceanic terranes, the interior Kahiltna assemblage, and the northern continental margin. Analyzed detrital zircons from each component of the Alaska Range suture zone provide information on the sedimentary provenance, the timing of collision, and the crustal evolution of the Mesozoic collisional zone. U-Pb and Hf isotopic analyses from detrital zircons of the oceanic Wrangellia terrane exhibit Mississippian-Pennsylvanian ages with Hf isotopic compositions that are entirely juvenile. U-Pb and Hf isotopic analyses for detrital zircons from the continental margin contain Paleozoic-Precambrian ages that show juvenile, intermediate, and evolved epsilon Hf_(t) values. U-Pb and Hf isotopic analyses from the interior sedimentary strata of Jurassic-Cretaceous Kahiltna assemblage display Precambrian-Mesozoic ages with an assortment of juvenile to evolved epsilon Hf_(t) values. To further delineate the tectonic development of the Mesozoic suture zone, we investigate the interior region between the accreted oceanic terranes and the continental margin. We report 2026 U-Pb detrital zircon analyses from Mesozoic sedimentary strata that represent pre- and postcollisonal stages associated with the suture zone in south-central Alaska. Detrital zircon samples obtained from the northern Talkeetna Mountains yields young detrital zircon peak ages that are (1) Early Jurassic with a peak age of 194 Ma and (2) late Early to early Late Cretaceous (Albian- Turonian) with young detrital zircon peak ages at 106, 105, 100, 95, and 90 Ma. The analyzed sample containing the young detrital zircon peak age of Early Jurassic is likely related to the base of the Kahiltna assemblage; representing precollisonal strata. Analyzed samples containing late Early to early Late Cretaceous detrital zircon ages are interpreted to be equivalent to the nonmarine strata of the Albian Caribou Pass formation in the northwestern Talkeetna Mountains; representing postcollisonal strata. The combined datasets presented herein allow for a revised tectonic model on the development of the Alaska Range suture zone.