NSF Award
1728013
The North American Cordillera was assembled through the formation, accretion, and translation of a number of terranes and much of this assembly has occurred since the Cretaceous. Since this time, most of the terrane translation was northward due to the relative motion of Pacific plates with North America. Despite decades of investigations on terrane movement and translation much remains unknown about where these terranes originated and how far they traveled before becoming part of the amalgamation of terranes in Alaska. This project brings new analytical techniques to bear on this problem focusing on the Yakutat terrane, which is now colliding with southern Alaska driving the uplift of the Chugach Range. This research tests the idea that the Yakutat terrane originated far to the south in the Pacific Northwest and moved parallel to the continental margin before colliding with southern Alaska. The project would advance desired societal outcomes by participation of students from underrepresented minorities in STEM, increased public scientific literacy and public engagement with STEM through development of brochures for the National Parks and National Forests and development of a diverse, globally competitive STEM workforce through active participation of undergraduate students in research at primarily undergraduate institutions.<br/><br/>The development and translation history of the collage of terranes that make up most of Alaska are debated, including the Chugach and Prince William terranes, and Yakutat terrane. Some scenarios envision a setting for the Chugach and Prince William terranes that was more or less in place, while other scenarios (originally based on paleomagentic data) suggest long transport (>3000 km). The difference in these ideas is profound, but large-scale translation of terranes on strike-slip faults may be a fundamental and underappreciated process in the Cordillera. High-precision and high-volume U/Pb and fission track dating of detrital zircon has focused the lens with which the problem can be examined, and rigorous predictions can be made by making geological comparisons of units along the Cordilleran margin to better understand translation history and total offset. Preliminary data show a number of assumptions about the Chugach-Prince William terrane and Yakutat terrane collision zone need to be revised, including: (1) turbidites of the Yakutat terrane may not be part of the Chugach and Prince William terranes as previously assumed; and (2) the basaltic basement of the Yakutat terrane may have formed in a transtensional environment along the North American margin. The hypothesis tested here is that transport of the Yakutat terrane to Alaska resulted in a truncated margin in the Pacific Northwest, and slip on the Queen Charlotte-Fairweather fault system may have partly accommodated the 1800 km of dextral translation, which may be one of the longest offsets shown by geological relationships on faults in the Cordillera. The analytical approach of this research involves the analysis of detrital zircon using several techniques, some of which are new and innovative. These approaches include: (a) U/Pb of detrital zircon to determine maximum depositional age and provenance, including targeting Precambrian sources; (b) fission track on detrital zircons to provide cooling ages directly related to exhumation, including double dating grains (fission track and U/Pb); (c) Raman spectroscopy on detrital to provide radiation damage dates; (d) Hf isotopes in detrital zircon to provide crustal signature; and (e) core-rim dating to date igneous and metamorphic rims. Determining radiation damage ages on detrital zircon is a new approach that promises to provide deeper insight into detrital studies. Although zircon is central to this effort, student projects that use geochemistry and petrology will focus on better understanding the development of the igneous rocks associated with these terranes.
