Chemostratigraphy of subduction initiation; boninite and forearc basalt from IODP Expedition 352

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Author(s): Shervais, John; Haugen, Emily; Godard, Marguerite; Ryan, Jeffrey G.; Prytulak, Julie; Li Hongyan; Chapman, Timothy; Nelson, Wendy R.; Heaton, Daniel E.; Kirchenbaur, Maria; Shimizu, Kenji; Li Yibing; Whattam, Scott A.; Almeev, Renat; Sakuyama, Tetsuya; Reagan, Mark K.; Pearce, Julian A.
Author Affiliation(s): Primary:
Utah State University, Department of Geology, Logan, UT, United States
Other:
Université Montpellier II, Geosciences Montpellier UMR 5243, France
University of South Florida, Department of Geology, United States
Imperial College London, Department of Earth Science & Engineering, United Kingdom
Chinese Academy of Sciences, Guangzhou Institute of Geochemistry, China
University of Sydney, School of Geosciences, Australia
Towson University, Department of Physics, Astronomy, and Geosciences, United States
Oregon State University, United States
Universität Köln, Geologisches Institut, Germany
Japan Agency for Marine-Earth Science and Technology, Japan
Chinese Academy of Geological Science, Institute of Geology, China
Korea University, South Korea
Institut für Mineralogie, Germany
University of Iowa, United States
Cardiff University, United Kingdom
Volume Title: European Geosciences Union general assembly 2017
Source: Geophysical Research Abstracts, Vol.19; European Geosciences Union general assembly 2017, Vienna, Austria, April 23-28, 2017. Publisher: Copernicus GmbH on behalf of the European Geosciences Union (EGU), Katlenburg-Lindau, Germany. ISSN: 1029-7006
Note: In English
Summary: The Izu-Bonin forearc has been the focus of several recent IODP (International Ocean Discovery Program) expeditions studying the geophysical, petrologic, and chemical response to subduction initiation and its potential relationship to ophiolite genesis. IODP Expedition 352 cored four holes in the Izu-Bonin forearc near Chichi Jima in order to document the petrologic and chemical evolution of nascent subduction zones. Holes U1440 and U1441, drilled closest to the trench, sampled forearc basalt (FAB). U1439 and U1442, drilled stratigraphically up-section and farther from the trench, sampled boninite, high-Mg andesite, and basalt. FAB are characterized by MORB-like compositions, with relatively constant Ti, Zr, and Ti/Zr. In general, more primitive FAB are found in the lower part of the section. In detail, FAB have lower Na, Ti, P, and Zr, lower Ti/V ratios, and are LREE-depleted relative to MORB. Best fit models for the least evolved FAB and a depleted MORB mantle (DMM) source require extraction of ∼1% melt in the garnet lherzolite field and 19% melt extraction in the spinel lherzolite field (relative to 8-10% melt of DMM to produce MORB). Three types of boninite were found: high silica boninite (HSB), low silica boninite (LSB), and basaltic boninite (BB), as well as high Mg andesites (HMA). HSB, the youngest unit in both U1439 and U1442, is underlain by LSB-BB-HMA lavas, which often occur in mixed magma zones with evolved boninite and basalt. Boninites are distinguished by co-variations in SiO2-MgO and TiO2-MgO, and by Ti/Zr ratios, which increase from HSB through LSB to BB. HSB, LSB and BB define parallel trends in TiO2-MgO space: a low Ti trend represented by LSB and BB, and a lower Ti trend represented by HSB. All of the boninite suite rocks are slightly LREE-rich relative to MORB. LSB and BB have flat REE patterns relative to primitive mantle, whereas HSB are slightly LREE-rich. These trends require distinct source compositions in HSB relative to LSB/BB. The decrease in Ti/Zr from BB to HSB suggests a slab melt component. Melting models (non-modal, fractional) for boninites require additional partial melting of a residual source more depleted than DMM, and mixing with less depleted melts. The data require a heterogeneous source during subduction initiation, tapping progressively more refractory mantle through time, and showing progressive enrichment in slab components. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 02 Geochemistry; Andesites; Basalts; Boninite; Chemostratigraphy; Expedition 352; IODP Site U1439; IODP Site U1440; IODP Site U1441; IODP Site U1442; Igneous rocks; International Ocean Discovery Program; North Pacific; Northwest Pacific; Pacific Ocean; Volcanic rocks; West Pacific
Coordinates: N282427 N282427 E1424633 E1423631
N282659 N282700 E1424513 E1424513
N282538 N282538 E1424332 E1423332
Record ID: 2018023582
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from European Geosciences Union, Munich, Germany