Pacific Section AAPG Convention

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Early Subduction And Depositional History Of The Izu-Bonin Mariana Arc Back-Arc System, Western Pacific Ocean


Subduction zones are a vital component of plate tectonics; slab pull at subduction zones is a major driver of plate movement. However, we have incomplete understanding of how the subduction process begins. In particular, records are lacking for intraoceanic arc subduction systems. The International Ocean Discovery Program recently sampled sediments at several locations in one such arc, the Izu-Bonin Mariana Arc south of Japan. These sediments will provide a previously lacking window into the early development of this subduction zone. I propose that subduction in the Izu-Bonin Mariana Arc System initiated spontaneously along a transform plate boundary. This mode of subduction initiation leaves a characteristic stratigraphic sequence associated with pre subduction-initiation localized extension and subsidence followed by volcanism and volcanic uplift as subduction begins. I am testing this hypothesis by examining sediment cores from two sites in the IBM arc system; one at the northern end of the arc, and one at the southern end. A detailed macroscopic study of the cores is being conducted to identify depositional features and trends, and microscopic analysis of selected intervals to identify mineralogy and microstructures. This will facilitate creating a detailed stratigraphic record of the arc, giving us a much better understanding of its earliest depositional history, and allow the changes in environment over time to be correlated with the predicted model of spontaneous subduction initiation.