Accretionary prisms form as sediments are collected (i.e., accreted) and complexly deformed at the down-going edge of a subducting oceanic plate. Accretionary prisms provide evidence of convergence in the geologic record and are a significant mechanism for the growth of continental crust. Some accretionary prisms in subduction zones experience long periods of erosion, rather than accretion, which has led the PIs to propose investigating the triggers for accretion vs. erosion. The Chugach terrane in Alaska has long been considered as a type example of an accretionary prism. The PIs will relate rock-type variations in the accretionary prism to major tectonic events in North America. Structural geology and detrital zircon ages will be used to determine if these variations represent distinct accretionary episodes or a continuum of accretion. They will study the flysch to constrain its accretionary history using regional geology as a proxy for sediment supply. This project will elucidate processes of subduction erosion that impact general models of geochemical cycling in the Earths interior.
Geologists have long realized that many of the features of the Earth, as well as the causes of natural hazards, are related to the processes by which the large tectonic plates move into the interior of the Earth during subduction. Subduction leads to volcanism, such as that seen in the Cascades, and subduction caused the largest earthquakes ever recorded, such as in Alaska in 1964. Studying the sediment accreted above the subducting plate will help us understand this subduction process. In addition, accretionary prisms have the potential to host mineral deposits and could provide a source of methane that would enhance global warming. This project will also help us to understand the history of Alaska and provide for the education of undergraduate and graduate students at minority-serving institutions in the southwest U.S.
