Developing a tephra database to document the evolution of explosive volcanism along the Gulf of Alaska margin for the past six million years

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Explosive volcanism can be influenced by a range of geologic and climatic processes. In areas like the Gulf of Alaska, both the rate and angle of convergence of tectonic plates are understood to influence the rate of explosive volcanism. Less well understood is the influence of glaciers and whether climate fluctuations resulting in the ebb and flow of glaciers indirectly impact eruption frequency through increased erosion rates. Gaining a better understanding of how these factors contribute to explosive volcanic frequency can inform us on the nature of particular tectonic subduction zones like the Gulf of Alaska, helping mitigate the impact of potential volcanic hazards on vulnerable populations. The Gulf of Alaska margin is one of the most volcanically active regions in the world, making it a good area for study. However, continuous records of past volcanism in this region are rare due to extensive glaciation and erosion during over the past 2.5 million years. The high-quality deep-sea cores collected during the Integrated Ocean Drilling Program (IODP) Expedition 341 to the southern Alaskan margin provide new and rare material to examine volcanism in this region during key tectonic and climatic events. The proposed work seeks to develop a database of volcanic material from these cores to quantify the development and evolution of Gulf of Alaska volcanism during key tectonic and climate events over the past six million years.Technical Description: The proposed work will identify and develop a geochemical and geochronological database for tephras from IODP sites U1417 & U1418. A combination of data will be collected to (i) determine tephra sources from the region?s three major volcanic provinces; (ii) reconstruct the late Miocene-to-present evolution of eruptive volcanism along the Gulf of Alaska Margin; (iii) design a marine tephra database for use in terrestrial paleoclimatic studies. Methods will include microscope and magnetic susceptibility identification of tephra, grain-specific major and trace element geochemical fingerprinting, and 40Ar/39Ar radiometric dating of glass, hornblende, biotite, and/or sanidine. Results will be integrated with paleomagnetic, oxygen-18 isotope and microfossil chronostratigraphies of Sites U1417 & U1418, as well as with existing terrestrial Alaskan and Canadian Yukon tephra data. The overall results of this research will provide new constraints on (i) the effect of different tectonic-climate boundary forces on eruptive volcanic frequency, (ii) the genetic relationships between variations in eruption rate and the initiation of the Northern Hemisphere glaciations, and (iii) create a public database of well-dated geochemically fingerprinted marine tephras to provide an improved framework for reconstructing the paleoclimatic history of Alaska and the Yukon.