GEOLOGY, U-PB GEOCHRONOLOGY, AND HAFNIUM ISOTOPE GEOCHEMISTRY ACROSS THE ALASKA RANGE SUTURE ZONE (SOUTH-CENTRAL ALASKA): INSIGHTS INTO COLLISIONAL PROCESSES AND CORDILLERAN TECTONICS

The development of the Alaska Range suture zone involves the amalgamation of the allochthonous Wrangellia composite terrane to the Mesozoic northwestern continental margin of North America. In south-central Alaska, the Alaska Range suture zone is defined by a transition from outboard oceanic terranes to inboard continental margin terranes. Mesozoic and Cenozoic sedimentary strata are exposed between the oceanic and continental terranes; these strata record the progressive development of the collisional zone. Along with a revised stratigraphy, we utilize the detrital zircon record to provide new insights into the paleogeographic setting, the timing of collision, and the deep crustal processes within this Mesozoic collisional zone. We present 3456 U-Pb analyses and 491 Hf isotopic compositions of detrital zircons from across the suture zone. New maximum depositional ages have been constrained from samples that have been obtained from the oceanic Wrangellia composite terrane, the intervening sedimentary strata, and the continental margin belt. Analyzed detrital zircons of the Wrangellia composite terrane primarily derive from magmatic sources associated with distinct Mesozoic stages of oceanic arc growth. The Paleozoic and abundant Precambrian ages of detrital zircons from the continental margin belt originate from igneous rocks and pericratonic crustal material of the North American Cordillera. Precambrian-Cenozoic magmatic sources of detrital zircons from the intervening sedimentary strata represent a mixture of detritus from various sources with increasing amounts of North American detritus in younger strata. This is the first study utilizing Hf isotopic analyses across the Alaska Range suture zone. Hf isotopic compositions are entirely juvenile with epsilon Hf_(t) values between +17 and +10 for the Wrangellia composite terrane. Hf analyses of the detrital zircons from the continental margin belt show juvenile, intermediate, and evolved epsilon Hf_(t) values; ranging between +10 and -20. There is an assortment of juvenile to evolved epsilon Hf_(t) values between +14 and -19 for the intervening sedimentary strata. Combining these new data sets, we present a revised model for the collisional processes associated with the growth of northwestern Cordillera during the Mesozoic.