COMPARATIVE PROVENANCE APPROACHES FOR CONSTRAINING TRENDS IN EXHUMATION, SEDIMENT DISPERSAL, AND PALEOGEOGRAPHY FROM UPPER PALEOZOIC STRATA OF THE FAREWELL TERRANE, SW ALASKA
U-Pb detrital zircon age spectra from Silurian-Devonian strata of the Dillinger subterrane show primary peak ages between 425-450 Ma and secondary peak ages between 550-700 Ma. Paleozoic-Neoproterozoic detrital zircons exhibit both enriched (-1 to -15) and depleted (+2 to +14) epsilon Hf values. Modal composition trends reveal pervasive occurrences of mono- and polycrystalline quartz (~46%) and subordinate occurrences of chert, plagioclase, and lithic metamorphic and volcanic fragments. Overall, provenance trends reflect strong contributions from recycled orogen source areas that likely included both enriched and depleted mantle reservoirs.
U-Pb detrital age spectra from Devonian-Permian strata of the Mystic subterrane show primary peak ages between 280-310, 330-375, and 415-460 Ma and secondary peak ages between 1820-1980 Ma. Pennsylvanian-Permian detrital zircons exhibit depleted epsilon Hf values (+2 to +14) whereas Devonian-Mississippian zircons have enriched signatures (epsilon Hf values between -5 and -35). Ordovician-Silurian zircons exhibit both enriched (-5 to -25) and depleted (+5 to +14) epsilon Hf values. Compositional trends show a relative abundance of lithic volcanic fragments (~65%) and subordinate occurrences of chert and lithic sedimentary fragments. Overall, provenance trends reflect contributions from arc source areas that included enriched and depleted mantle reservoirs.