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Strategic IODP Planning Workshop for Ultra-Deep Drilling into Arc Crust
Two U.S. Geological Survey (USGS) geologists—Amy Draut of the Pacific Coastal and Marine Science Center in Santa Cruz, California, and Erin Todd of the Alaska Science Center in Anchorage—were among 58 international scientists who gathered in Kona, Hawai'i, from September 17 to 21, 2012, for a planning workshop on "Ultra-Deep Drilling into Arc Crust" by the International Ocean Discovery Program (IODP; formerly the Integrated Ocean Drilling Program).
The participants were geophysicists, geologists, geochemists, and petrologists interested in the nature of oceanic-arc crust, how it is modified by collisions at subduction zones, and how it is incorporated and preserved in continental crust. These research problems are fundamental to the next decade of IODP science, one goal of which is to address "how… subduction zones initiate, cycle volatiles, and generate continental crust." (See Challenge 11 of the program's Science Plan for 2013–2023.)
Oceanic arcs are volcanic chains, such as the Mariana Islands, that form above subduction zones where one slab of thin oceanic crust is sliding beneath another. (In contrast, other subduction zones occur where thin, dense oceanic crust slides beneath thicker, less dense continental crust, forming a continental volcanic chain, such as the Andes Mountains.) Scientists have known for decades that oceanic crust is produced at seafloor-spreading ridges, but the production of continental crust—generally considered to begin in subduction zones—is not well understood. IODP investigation of oceanic-arc subduction zones will help elucidate the process of continental-crust formation.
The planning workshop included 3 days of talks and discussions; for a change of pace, the participants also took a 1-day field trip to nearby Kilauea Volcano, Hawai'i's most active volcano. Draut presented an invited talk at the workshop, summarizing the role of arc-continent collisions in producing and modifying continental crust.
Workshop scientists discussed the merits, methods, and implications of drilling more than 6 kilometers (4 miles) below the seafloor in the Izu-Bonin-Mariana arc offshore of Japan with the riser-equipped deep-sea drilling vessel (D/V) Chikyu. The proposed drilling is a unique opportunity to sample young continental-type crust, to observe the mid-crustal processes that produce the nuclei of new continental crust, and to examine the nature of juvenile continental crust as first generated at oceanic arcs.
As noted in the workshop report, "For the first time in human history, ultra-deep drilling can reach juvenile continental crust that has never been re-processed" and thus shed new light on continental-crust formation. Scientists also hope that ultra-deep drilling will help them link processes active at specific levels in the arc crust with geophysical signals, and so enable the use of such signals to infer processes in other active arcs.
The IODP ultra-deep-drilling leg, which could take place as early as 2014, is sponsored jointly by JAMSTEC (Japan Agency for Marine-Earth Science and Technology) and the National Science Foundation.
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