PROVENANCE CONSTRAINTS ON EROSION, EXHUMATION, AND SEDIMENT DISPERSAL FROM UPPER PALEOZOIC STRATA OF THE FAREWELL TERRANE, SW ALASKA

The Farewell terrane of southwestern Alaska is located at the northernmost endpoint of the North American Cordillera and is defined by a three-part succession that consist of (1) Neoproterozoic–Devonian carbonate rocks and subordinate clastic strata of the Nixon Fork subterrane, (2) Cambrian–Devonian clastic and carbonate units of the Dillinger subterrane, and (3) Devonian–Permian(?) siliciclastic strata of the Mystic subterrane. Although previous studies have suggested a Siberian origin for the oldest parts of the Farewell, it has yet to be determined if the Dillinger and Mystic subterranes share links with regions to the north (e.g. Siberia, Baltica, Greenland) or with the northern and western regions of Laurentia. Presented here are U-Pb ages and Hf isotopic compositions from detrital zircon as well as modal composition trends from Paleozoic strata of the Dillinger and Mystic subterranes that reflect an upsection transition in detrital contribution from the Farewell terrane.

U-Pb detrital zircon age spectra from Silurian–Devonian strata of the Dillinger subterrane reveal a range of Precambrian and Paleozoic ages with primary peak ages between 425–450 and 900–975 Ma at 1400 and 1700 Ma. Isolated ages occur at 1000, 1800, 2700, and 3000 Ma. Overlying strata of the Mystic subterrane have primary peak ages between 275–300 and 425–450 Ma with isolated occurrences at 650, 950, 1300, 1500, 1700, and 2600 Ma. Detrital zircons from Dillinger and Mystic subterranes exhibit a range of positive and negative εHf values and that may imply exhumation of both juvenile and crustally-contaminated magmatic source areas. Modal composition trends reveal pervasive occurrences of mono- and polycrystalline quartz, plagioclase, as well as a strong lithic volcanic component reflective of arc and recycled origin source areas.

Preliminary provenance trends from the Dillinger subterrane potentially reflect an initial stage of exhumation and detrital contributions from sources areas along the eastern and central Uralian Seaway (e.g. Baltica, Siberia, and Taimyr regions). Provenance trends from the Mystic subterrane may reflect and introduction of detritus from the northern or western margins of Laurentia potentially reflecting a paleogeographic location in the central to western Uralian seaway by Late Paleozoic time.