This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
This research group will give one of the first detailed accounts of the sedimentary basin response to oceanic spreading-ridge subduction, a common tectonic process that fundamentally reshapes and reorganizes convergent continental margins. Forearc basins, one of the most common along convergent margins, are large sediment repositories that have the potential to preserve a detailed record of spreading-ridge subduction processes. Preliminary work indicates that the Matanuska Valley region of southern Alaska is a fertile area, perhaps the best on Earth, to examine the long term sedimentary record of spreading-ridge subduction in a forearc basin. The proposed research also has direct implications for US citizens. The Paleocene?Eocene strata to be studied are economically important for coal and methane reserves. Understanding ridge subduction will also be important for hydrocarbon exploration in the forearc basin in the Cook Inlet. In addition, a major objective of the research is better characterization of the Castle Mountain fault system, activity along which presents a serious hazard for >300,000 people that live in the Anchorage-Palmer-Wasilla region. The scientific outreach plan involves a two-day field trip with K?12 Native American students from rural Alaskan communities, as well as undergraduate students from the University of Alaska, where they will learn about one of the best exposed convergent margins on Earth. The PIs will help students understand the impact of tectonic processes that shape their local environment and communities. The Native American students have grown up around geological issues (gold and coal mining, petroleum exploration, earthquakes, etc.), but many probably have not made connections between these issues and tectonic processes along convergent margins.
Forearc basin strata in south-central Alaska provide a superb opportunity to study sedimentary basin response to spreading ridge subduction. Well-exposed strata over 2800 m thick crop out in the Matanuska Valley region between Cretaceous-Paleocene arc plutons to the north and Cretaceous accretionary prism strata to the south. The proposed interdisciplinary study will evaluate three hypotheses: (1) That the main phase of Paleocene-Eocene basin development and sediment accumulation was synchronous with spreading ridge subduction and slab window magmatism in southern Alaska; (2) That spreading ridge subduction modified the depositional and structural configuration of the basin, resulting in subaerial uplift of the formerly marine forearc basin followed by rapid subsidence and nonmarine deposition; and (3) That spreading ridge subduction triggered exhumation of arc plutons and metamorphic rocks, and that this process is recorded in the detrital composition of the forearc basin strata. A new approach in the proposed research is that strata of the forearc basin will be used to not only determine the types of magmatic and sedimentary processes that occur in forearc basins during ridge subduction but also to serve as a bridge for understanding the timing of related processes across both the accretionary prism and the magmatic arc parts of convergent margins.
