Journal article
Radiogenic isotopes document the start of subduction in the Western Pacific
Earth and Planetary Science Letters, Vol.518, pp.197-210
07/15/2019
DOI: 10.1016/j.epsl.2019.04.041
Abstract
•IODP Exp. 352 (Bonin Forearc) cored 52–50 Ma subduction initiation lavas and dikes.•Hf–Nd–Sr–Pb isotopes reveal that magma genesis changed rapidly over this 2 m.y. period.•First, forearc basalts tapped an ambient, depleted, ‘Indian-domain’ mantle reservoir.•Then boninites tapped residual mantle fluxed by shallow ‘Pacific domain’ slab melt.•Finally subducted Pacific pelagic sediments generated further boninite magmatism. Subduction initiation is one of the least understood aspects of plate tectonics. In an effort to obtain the first in situ magmatic record of subduction initiation, the International Ocean Discovery Program Expedition 352 drilled at four sites in the inner trench wall of the Bonin Trench to recover 1.22 km of oceanic upper crust accreted within a few m.y. of subduction initiation. The two sites nearer to the trench (U1440 and U1441) yielded axial and off-axis fore-arc basalts (FAB), while those c. 15 km further from the trench (U1439 and U1442) yielded axial low-silica boninites and high-Mg andesites overlain by off-axis high-silica boninites. This study uses Hf–Nd–Sr–Pb isotope analyses from c. 50 stratigraphically representative core samples to trace the evolution of the mantle source during the brief period of FAB-through-boninite magmatism immediately following subduction initiation. Results show that: 1) the FAB have high εHf relative to εNd and were derived from variably depleted mantle of ‘Indian’ provenance with no detectable subduction input; 2) the axial boninites follow mixing trends between a residual FAB mantle source and a subduction component derived from shallow (amphibolite facies) melting of oceanic crust of ‘Pacific’ provenance; and 3) the off-axis boninites define mixing trends between a hybrid mantle wedge (residual mantle + slab melt) and an additional subduction component with lower εNd and higher 207Pb/204Pb that requires a significant contribution from pelagic sediment. This incoming of pelagic sediments may signify a change from an accretionary to non-accretionary margin as subduction evolves. The results thus indicate a rapidly evolving system in terms of geodynamics, magma genesis and crustal accretion immediately following subduction initiation.
Details
- Title: Subtitle
- Radiogenic isotopes document the start of subduction in the Western Pacific
- Creators
- Hong-Yan Li - State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, PR ChinaRex N Taylor - School of Ocean and Earth Science, University of Southampton, NOC, Southampton, SO14 3ZH, UKJulie Prytulak - Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, UKMaria Kirchenbaur - Institut für Mineralogie, Universität zu Köln, GermanyJohn W Shervais - Department of Geology, Utah State University, Logan, UT, USAJeffrey G Ryan - School of Geosciences, University of South Florida, Tampa, FL, USAMarguerite Godard - Géosciences Montpellier, CNRS, Université de Montpellier, Montpellier, FranceMark K Reagan - Department of Earth and Environmental Sciences, University of Iowa, Iowa City, IA, USAJulian A Pearce - School of Earth and Ocean Sciences, Cardiff University, Cardiff CF10 3AT, UK
- Resource Type
- Journal article
- Publication Details
- Earth and Planetary Science Letters, Vol.518, pp.197-210
- Publisher
- Elsevier B.V
- DOI
- 10.1016/j.epsl.2019.04.041
- ISSN
- 0012-821X
- eISSN
- 1385-013X
- Grant note
- DOI: 10.13039/501100004872, name: State Oceanic Administration; DOI: 10.13039/501100008982, name: National Science Foundation; DOI: 10.13039/501100000270, name: Natural Environment Research Council; DOI: 10.13039/501100002367, name: Chinese Academy of Sciences
- Language
- English
- Date published
- 07/15/2019
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9983983653402771
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