HF ISOTOPE SIGNATURES OF DETRITAL PRECAMBRIAN ZIRCON SUGGEST A SOUTHERN LAURENTIAN SOURCE FOR THE UPPER CRETACEOUS FLYSCH OF THE CHUGACH-PRINCE WILLIAM TERRANE, ALASKA

An outstanding question in the construction of the North American Cordillera through the accretion of tectonstratigraphic terranes throughout the Phanerozoic is the amount of coastwise translation these terranes experienced since accretion. Plate reconstructions show that convergence between oceanic lithosphere and North America from mid-Cretaceous time to present had a significant dextral strike-slip component. However, there is considerable debate as to the number of oceanic plates and the amount of dextral strike-slip motion experienced by various terranes in the overriding plate.

In this contribution, we present combined U/Pb and Hf isotope analyses of 213 Precambrian detrital zircons from the Upper Cretaceous and Paleocene flysch of the Chugach-Prince William terrane (CPW) in southern Alaska. Precambrian zircons from western units of the CPW have a wide range of grain ages with modes at 1810-1870 Ma and 2520-2680 Ma with εHf(t) from -21.1 to +13.9. Zircon from the eastern units of the CPW (basement of the Yakutat terrane) have modes at 1380-1450 Ma and 1710-1740 Ma with εHf(t) from -3.4 to +11.7. Mesoproterozoic and late Paleoproterozoic (<1750 Ma) zircons from the CPW have εHf(t) > -5 and all zircons between 1436 and 1716 Ma have positive εHf(t) values. The dominance of Mesoproterozoic and late Paleoproterozoic ages with mostly positive Hf isotope signatures from the eastern part of the CPW suggests that these rocks were derived from a source terrane dominated by younger, juvenile Precambrian crust typical of southern Laurentia (i.e. Yavapai-Mazatzal crust). This result requires substantial northward transport of sediment, terranes, or both.