Geology, U‐Pb Geochronology, and Hf Isotope Geochemistry Across the Mesozoic Alaska Range Suture Zone (South‐Central Alaska): Implications for Cordilleran Collisional Processes and Tectonic Growth of North America. Issue 3 (5th March 2020) - Romero, Mariah C.
Abstract: The Mesozoic Alaska Range suture zone is defined by a transition from oceanic to continental terranes and is part of a 2000‐km‐long tectonic boundary throughout the northern Cordillera. Surface geologic mapping of the rock types across this suture zone provides critical information about the upper crustal configuration but provides little insight into the sedimentary, igneous, and metamorphic processes that occurred in deeper levels of the collisional zone. To better constrain the timing and mantle‐crust sources of collision‐related magmatism, we combine U‐Pb ages and Hf isotope compositions of detrital zircons from the three main components of the suture zone. U‐Pb/Hf data sets from inboard, continental margin samples have Precambrian‐Paleozoic ages with epsilon Hf(t) values ranging between +10 and −20. U‐Pb/Hf data sets from the outboard, oceanic terrane samples have Pennsylvanian‐Permian detrital zircon ages with epsilon Hf(t) values between +16 and +10. The U‐Pb/Hf data set of detrital zircons from Mesozoic strata that represent intervening sedimentary basin(s) that formed between the continental margin and oceanic terranes record Precambrian‐Mesozoic detrital zircon ages with epsilon Hf(t) values between +14 and −20. Results of the study document four Archean and Proterozoic global crustal magmatic events that are correlated to the tectonic growth of Laurentia. Also, three Phanerozoic magmatic events have been identified that represent more regional tectonic events. This study demonstrates that the combination of U‐Pb geochronology and Hf isotope geochemistry applied to detrital zircons is a powerful tool to define sediment provenance in collisional zones and delineate episodes of global and regional magmatism along convergent plate boundaries. Key Points: The Alaska Range suture zone (ARSZ) represents part of a 2000‐km‐long crustal boundary that records the tectonic growth of North America Detrital zircon U‐Pb ages and Hf isotope compositions from the ARSZ record magmatic events associated with global and regional tectonics Integration of multiple data sets from detrital zircons provides new insights into sediment provenance in collisional zones