International Ocean Discovery Program Expedition 352 Preliminary Report; Izu-Bonin-Mariana fore arc; testing subduction initiation and ophiolite models by drilling the outer Izu-Bonin-Mariana fore arc; 30 July-29 September 2014

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doi: 10.14379/
Author(s): Pearce, Julian A.; Reagan, Mark K.; Petronotis, Katerina; Morgan, Sally; Almeev, Renat; Avery, Aaron J.; Carvallo, Claire; Chapman, Timothy; Christeson, Gail L.; Ferré, Eric C.; Godard, Marguerite; Heaton, Daniel E.; Kirchenbaur, Maria; Kurz, Walter; Kutterolf, Steffen; Li Hongyan; Li Yibing; Michibayashi, Katsuyoshi; Nelson, Wendy R.; Prytulak, Julie; Python, Marie; Robertson, Alastair H. F.; Ryan, Jeffrey G.; Sager, William W.; Sakuyama, Tetsuya; Shervais, John W.; Shimizu, Kenji; Whattam, Scott A.
International Ocean Discovery Program, Expedition 352 Scientists, College Station, TX
Author Affiliation(s): Primary:
Cardiff University, School of Earth and Ocean Sciences, Cardiff, United Kingdom
University of Iowa, United States
International Ocean Discovery Program, United States
University of Leicester, United Kingdom
Leibniz University of Hanover, Germany
Florida State University, United States
Université Pierre et Marie Curie, France
University of Sydney, Australia
University of Texas-Austin, United States
Southern Illinois University-Carbondale, United States
Université de Montpellier II, France
Oregon State University, United States
Universität Kõln, Germany
University of Graz, Austria
Helmholtz Centre for Ocean Research, Germany
Chinese Academy of Sciences, Guangzhou Institute of Geochemistry, China
Chinese Academy of Geological Science, China
Shizuoka University, Japan
University of Houston, United States
Imperial College London, United Kingdom
Hokkaido University, Japan
University of Edinburgh, United Kingdom
University of South Florida-Tampa, United States
Japan Agency for Marine-Earth Science and Technology, Japan
Utah State University, United States
Korea University, South Korea
Source: Preliminary Reports (International Ocean Discovery Program), Vol.352, 86p. Publisher: IODP Management International, College Station, TX, United States. ISSN: 2372-9562
Note: In English. 45 refs.
Summary: The objectives for Expedition 352 were to drill through the entire volcanic sequence of the Bonin fore arc to 1. Obtain a high-fidelity record of magmatic evolution during subduction initiation and early arc development, 2. Test the hypothesis that fore-arc basalt lies beneath boninite and understand chemical gradients within these units and across the transition, 3. Use drilling results to understand how mantle melting processes evolve during and after subduction initiation, and 4. Test the hypothesis that the fore-arc lithosphere created during subduction initiation is the birthplace of suprasubduction zone (SSZ) ophiolites. Expedition 352 successfully cored 1.22 km of igneous basement and 0.46 km of overlying sediment, providing diverse, stratigraphically controlled suites of fore-arc basalts (FAB) and boninite related to seafloor spreading and earliest arc development. FAB were recovered at the two deeper water sites (U1440 and U1441) and boninites at the two sites (U1439 and U1442) drilled up slope to the west. FAB lavas and dikes are depleted in high-field strength trace elements such as Ti and Zr relative to mid-ocean-ridge basalt but have relatively diverse concentrations of trace elements because of variation in degrees of melting and amount of subducted fluids involved in their genesis. All FAB magmas underwent significant crystal fractionation in a persistent magma chamber system. Holes U1439C and U1442A yielded entirely boninitic lavas. We defined three boninite differentiation series based on variations in MgO, SiO2, and TiO2 concentrations of the parental magmas. Lavas in both pairs of holes have compositions that generally become more primitive and have lower TiO2 concentrations upward. The presence of dikes at the base of the sections at Sites U1439 and U1440 provides evidence that boninitic and FAB lavas are both underlain by their own conduit systems and that FAB and boninite group lavas are likely offset more horizontally than vertically. We thus propose that seafloor spreading related to subduction initiation migrated from east to west after subduction initiation and during early arc development. Initial spreading was likely rapid, and an axial magma chamber was present. Melting was largely decompressional during this period, but subducted fluids affected some melting. As subduction continued and spreading migrated to the west, the embryonic mantle wedge became more depleted, and the influence of subducted constituents dramatically increased, causing the oceanic crust to be built of boninitic rather than tholeiitic magma. The general decrease in fractionation upward reflects the eventual disappearance of persistent magma chambers, either because spreading rate was decreasing with distance from the trench or because spreading was succeeded by off-axis magmatism trenchward of the ridge. The extreme depletion of the sources for all boninitic lavas was likely related to the incorporation of mantle residues from FAB generation. This mantle depletion continued during generation of lower silica boninitic magmas, exhausting clinopyroxene from the mantle such that the capping high-Si, low-Ti boninites were generated from harzburgite. Additional results of the cruise include recovery of Eocene to recent deep-sea sediment that records variation in sedimentation rates with time resulting from variations in climate, the position of the carbonate compensation depth, and local structural control. Three phases of highly explosive volcanism (latest Pliocene to Pleistocene, late Miocene to earliest Pliocene, and Oligocene) were identified, represented by 132 graded air fall tephra layers. Structures found in the cores and reflected in seismic profiles show that this area had periods of normal, reverse, and strike-slip faulting. Finally, basement rock P-wave velocities were shown to be slower than those observed during logging of normal ocean crust sites.
Year of Publication: 2014
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 05 Petrology, Igneous and Metamorphic; 18 Geophysics, Solid-Earth; Algae; Andesites; Basalts; Basins; Biostratigraphy; Boninite; Boreholes; Cenozoic; Cores; Crust; Expedition 352; Fore-arc basins; Geochemistry; IODP Site U1440; IODP Site U1441; IODP Site U1442; IODP Site U1493; Igneous rocks; International Ocean Discovery Program; Invertebrata; Island arcs; Izu-Bonin Arc; Lava; Lithostratigraphy; Magmas; Magmatism; Magnetostratigraphy; Major elements; Mantle; Marine sediments; Microfossils; Nannofossils; North Pacific; Northwest Pacific; Oceanic crust; Ophiolite complexes; Pacific Ocean; Parent materials; Petrology; Physical properties; Plantae; Plate tectonics; Protista; Quaternary; Radiolaria; Sea-floor spreading; Sedimentary rocks; Sediments; Subduction; Subduction zones; Tertiary; Tholeiite; Trace elements; Volcanic rocks; Volcanism; Well logs; West Pacific; Whole rock
Coordinates: N382427 N382427 E1423631 E1423631
N282659 N282659 E1424513 E1424513
N282538 N282538 E1424332 E1424332
N282435 N282435 E1423720 E1423720
Record ID: 2015017331
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