IODP Expedition 351 Izu-Bonin-Mariana arc origins; preliminary results

Author(s): Ishizuka, O.; Arculus, Richard J.; Bogus, K.
Author Affiliation(s): Primary:
Geological Survey of Japan, Ibaraki, Japan
Other:
Japan Agency for Marine-Earth Science and Technology, Japan
Australian National University, Australia
Integrated Ocean Drilling Program, United States
Volume Title: AGU 2014 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2014; American Geophysical Union 2014 fall meeting, San Francisco, CA, Dec. 15-19, 2014. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Understanding how subduction zones initiate and continental crust forms in intraoceanic arcs requires knowledge of the inception and evolution of a representative intraoceanic arc, such as the Izu-Bonin-Mariana (IBM) Arc system. This can be obtained by exploring regions adjacent to an arc, where unequivocal pre-arc crust overlain by undisturbed arc-derived materials exists. IODP Exp. 351 (June-July 2014) specifically targeted evidence for the earliest evolution of the IBM system following inception. Site U1438 (4711 m water depth) is located in the Amami Sankaku Basin (ASB), west of the Kyushu-Palau Ridge (KPR), a paleo-IBM arc. Primary objectives of Exp. 351 were: 1) determine the nature of the crust and mantle pre-existing the IBM arc; 2) identify and model the process of subduction initiation and initial arc crust formation; 3) determine the compositional evolution of the IBMarc during the Paleogene; 4) establish geophysical properties of the ASB. Seismic reflection profiles indicate a ∼1.3 km thick sediment layer overlying ∼5.5 km thick igneous crust, presumed to be oceanic. This igneous crust seemed likely to be the basement of the IBM arc. Four holes were cored at Site U1438 spanning the entire sediment section and into basement. The cored interval comprises 5 units: uppermost Unit I is hemipelagic sediment with intercalated ash layers, presumably recording explosive volcanism mainly from the Ryukyu and Kyushu arcs; Units II and III host a series of volcaniclastic gravity-flow deposits, likely recording the magmatic history of the IBM Arc from arc initiation until 25 Ma; Siliceous pelagic sediment (Unit IV) underlies these deposits with minimal coarse-grained sediment input and may pre-date arc initiation. Sediment-basement contact occurs at 1461 mbsf. A basaltic lava flow section dominantly composed of plagioclase and clinopyroxene with rare chilled margins continues to the bottom of the Site (1611 mbsf). The expedition successfully recovered pre-IBM Arc basement, a volcanic and geologic record spanning pre-Arc, Arc initiation to remnant Arc stages, which permits testing for subduction initiation and subsequent Arc evolution.
Year of Publication: 2014
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Cores; Expedition 351; IODP Site U1438; Integrated Ocean Drilling Program; Izu-Bonin Arc; Mariana Islands; Marine sediments; Micronesia; North Pacific; Northwest Pacific; Oceania; Pacific Ocean; Sediments; West Pacific
Record ID: 2015065219
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States

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