McCarthy, A, Yogodzinski, GM, Bizimis, M et al. (4 more authors) (2021) Volcaniclastic sandstones record the influence of subducted Pacific MORB on magmatism at the early Izu-Bonin arc. Geochimica et Cosmochimica Acta, 296. pp. 170-188. ISSN 0016-7037
Abstract
The remnant rear-arc segment of the early Izu-Bonin arc, known as the Kyushu-Palau Ridge (KPR), is a key location where magmatic outputs can be constrained during the lifetime of an island arc. We present new geochemical data for coarse-grained basaltic to andesitic volcaniclastic sandstones derived from the KPR and deposited in the Amami Sankaku Basin (IODP Site U1438, Unit III rocks) in the time period 40–30 Ma. Bulk disaggregated and cleaned volcaniclastic sandstones of Unit III at Site U1438 retain primary magmatic signatures and can be used to infer the evolution of magmatic sources of the juvenile Izu-Bonin island arc through time. A sharp increase of slab-derived components to the source of KPR magmatism developed at about 35 Ma, indicated by increasing Th/La and decreasing Sm/La, Yb/Hf and Nb/Nd. Systematic variations in trace element ratios and increasing trace element abundances in younger samples through the 40–30 Ma time window are decoupled from Hf-Nd isotope ratios, which are measurably more depleted (εHf = 16.5–15, εNd = 9.6–8.2) than boninites produced during the preceding magmatic phase and sampled in the modern Izu-Bonin forearc. Hafnium isotopic compositions in the Unit III sandstones remain little-changed and similar to the subducting Pacific Plate after 40 Ma and do not revert to highly radiogenic compositions of the Indian-type MORB mantle wedge which is reflected in highly-depleted basalts produced at Site U1438 and in the forearc (commonly εHf ≥ 18.0). The overall pattern recorded in Unit III sandstones indicates that the Pacific-type MORB slab-melt component, which was present in the preceding boninite phase of magmatism, persisted after 40 Ma, while the subducted sediment component in the boninite source was lost or significantly reduced. Variations in trace element ratios (at constant εNd and near-constant and radiogenic εHf) and in high field strength element abundances of the early Izu Bonin arc are controlled by the addition of a subducted Pacific MORB melt or supercritical fluid to the mantle wedge. A subducted MORB (slab melt) component is thus sampled throughout the early life of the Izu-Bonin arc and in the currently active Izu-Bonin arc-backarc system.
Metadata
Item Type: | Article |
---|---|
Authors/Creators: |
|
Copyright, Publisher and Additional Information: | © 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). |
Keywords: | IODP Exp. 351; Izu-Bonin arc; Slab melt; Radiogenic isotopes, Kyushu-Palau Ridge |
Dates: |
|
Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Funding Information: | Funder Grant number NERC (Natural Environment Research Council) NE/M007782/1 |
Depositing User: | Symplectic Publications |
Date Deposited: | 17 Feb 2021 14:18 |
Last Modified: | 17 Feb 2021 14:18 |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.gca.2021.01.006 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:171117 |