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Processes controlling along-arc isotopic variation of the southern Izu-Bonin arc

Processes controlling along-arc isotopic variation of the southern Izu-Bonin arc
Processes controlling along-arc isotopic variation of the southern Izu-Bonin arc
The southern Izu-Bonin arc is the volcanic representation of Pacific Ocean lithosphere subduction beneath the oceanic crust of the Philippine Sea plate. We present new geochemical data including high-precision Pb isotopic measurements from the 700 km length of this intraoceanic arc. An aim of this study is to link the along-arc characteristics with variations in the subducting Pacific crust. Chemical variations have been previously recognized along the northern section of the arc as a southward decrease in 87Sr/86Sr and increase in 206Pb/204Pb. This trend continues into the southern arc as far as 27.5°N. An overall correlation between 87Sr/86Sr and fluid-mobile element enrichment between 35 and 27.5°N implies a contribution of a slab-derived fluid, mainly from altered oceanic crust and pelagic sediment. However, the observation that volcanoes plot systematically closer to the Northern Hemisphere Reference Line (NHRL) with increasing 206Pb/204Pb indicates that a component other than pelagic sediment and ocean crust plays a key role toward the south. South of 27.5°N, the along-arc isotopic trend changes dramatically, with 87Sr/86Sr increasing southward from 27.5°N and the 206Pb/204Pb becoming highly radiogenic (?19.6). This isotopic signature requires involvement of a component with high 206Pb/204Pb and low ?8/4. Volcaniclastic sediments originating from HIMU oceanic islands on the subducting Pacific Plate are possible candidates to introduce such a component into the mantle wedge. This is consistent with the sedimentary section of ODP Site 801, located outboard of the Mariana arc which has >40% mass of HIMU volcaniclastics. An aqueous fluid, not melt, has played a major role in the source magma compositions in the 27.5–25°N segment. South of 25°N the isotopic characteristics again change significantly. 143Nd/144Nd decreases down to 0.51280, but the high 206Pb/204Pb and low ?8/4 signatures are retained. The remarkable Th enrichment associated with low 143Nd/144Nd, ?8/4, and ?7/4 suggests that melting a mixture of HIMU volcaniclastics and pelagic sediment is responsible for the geochemical characteristics of this most southerly section.

Izu-Bonin arc, slab component, HIMU, double-spike Pb
1525-2027
Q06008
Ishizuka, O.
8fe117e5-b0da-41ef-83ec-9e0bd6658747
Taylor, R.N.
094be7fd-ef61-4acd-a795-7daba2bc6183
Yuasa, M.
5a607459-19a9-42ea-b5cc-9e268eebb5a4
Milton, J.A.
9e183221-d0d4-4ddb-aeba-0fdde9d31230
Nesbitt, R.W.
6a124ad1-4e6d-4407-b92f-592f7fd682e4
Uto, K.
0970f5e1-2e96-40dc-9474-c6d3ba223a7e
Sakamoto, I.
56e895d0-e6d8-439b-8f64-02b82827eda3
Ishizuka, O.
8fe117e5-b0da-41ef-83ec-9e0bd6658747
Taylor, R.N.
094be7fd-ef61-4acd-a795-7daba2bc6183
Yuasa, M.
5a607459-19a9-42ea-b5cc-9e268eebb5a4
Milton, J.A.
9e183221-d0d4-4ddb-aeba-0fdde9d31230
Nesbitt, R.W.
6a124ad1-4e6d-4407-b92f-592f7fd682e4
Uto, K.
0970f5e1-2e96-40dc-9474-c6d3ba223a7e
Sakamoto, I.
56e895d0-e6d8-439b-8f64-02b82827eda3

Ishizuka, O., Taylor, R.N., Yuasa, M., Milton, J.A., Nesbitt, R.W., Uto, K. and Sakamoto, I. (2007) Processes controlling along-arc isotopic variation of the southern Izu-Bonin arc. Geochemistry, Geophysics, Geosystems, 8, Q06008. (doi:10.1029/2006GC001475).

Record type: Article

Abstract

The southern Izu-Bonin arc is the volcanic representation of Pacific Ocean lithosphere subduction beneath the oceanic crust of the Philippine Sea plate. We present new geochemical data including high-precision Pb isotopic measurements from the 700 km length of this intraoceanic arc. An aim of this study is to link the along-arc characteristics with variations in the subducting Pacific crust. Chemical variations have been previously recognized along the northern section of the arc as a southward decrease in 87Sr/86Sr and increase in 206Pb/204Pb. This trend continues into the southern arc as far as 27.5°N. An overall correlation between 87Sr/86Sr and fluid-mobile element enrichment between 35 and 27.5°N implies a contribution of a slab-derived fluid, mainly from altered oceanic crust and pelagic sediment. However, the observation that volcanoes plot systematically closer to the Northern Hemisphere Reference Line (NHRL) with increasing 206Pb/204Pb indicates that a component other than pelagic sediment and ocean crust plays a key role toward the south. South of 27.5°N, the along-arc isotopic trend changes dramatically, with 87Sr/86Sr increasing southward from 27.5°N and the 206Pb/204Pb becoming highly radiogenic (?19.6). This isotopic signature requires involvement of a component with high 206Pb/204Pb and low ?8/4. Volcaniclastic sediments originating from HIMU oceanic islands on the subducting Pacific Plate are possible candidates to introduce such a component into the mantle wedge. This is consistent with the sedimentary section of ODP Site 801, located outboard of the Mariana arc which has >40% mass of HIMU volcaniclastics. An aqueous fluid, not melt, has played a major role in the source magma compositions in the 27.5–25°N segment. South of 25°N the isotopic characteristics again change significantly. 143Nd/144Nd decreases down to 0.51280, but the high 206Pb/204Pb and low ?8/4 signatures are retained. The remarkable Th enrichment associated with low 143Nd/144Nd, ?8/4, and ?7/4 suggests that melting a mixture of HIMU volcaniclastics and pelagic sediment is responsible for the geochemical characteristics of this most southerly section.

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More information

Published date: 12 June 2007
Keywords: Izu-Bonin arc, slab component, HIMU, double-spike Pb

Identifiers

Local EPrints ID: 49711
URI: http://eprints.soton.ac.uk/id/eprint/49711
ISSN: 1525-2027
PURE UUID: bf08c49f-c711-45ac-a514-96d00d5de72b
ORCID for R.N. Taylor: ORCID iD orcid.org/0000-0002-9367-0294
ORCID for J.A. Milton: ORCID iD orcid.org/0000-0003-4245-5532

Catalogue record

Date deposited: 23 Nov 2007
Last modified: 16 Mar 2024 02:51

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Contributors

Author: O. Ishizuka
Author: R.N. Taylor ORCID iD
Author: M. Yuasa
Author: J.A. Milton ORCID iD
Author: R.W. Nesbitt
Author: K. Uto
Author: I. Sakamoto

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