Sedimentary and volcanic record of the nascent Izu-Bonin-Mariana arc from IODP Site U1438.

Waldman, Ryan J., Marsaglia, Kathleen M., Hickey-Vargas, Rosemary, Ishizuka, Osamu, Johnson, Kyle E., McCarthy, Anders, Yogodzinski, Gene, Samajpati, Eshita, Li, He, Laxton, Kate, Savov, Ivan P., Meffre, Sebastien, Arculus, Richard J., Bandini, Alexandre N., Barth, Andrew P., Bogus, Kara, Brandl, Philipp A. , Gurnis, Michael and Jiang, Fuqing (2021) Sedimentary and volcanic record of the nascent Izu-Bonin-Mariana arc from IODP Site U1438. Geological Society of America Bulletin, 133 (7-8). pp. 1421-1440. DOI 10.1130/B35612.1.

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Abstract

The oldest known, intact sedimentary record of a nascent intraoceanic arc was recovered in a ∼100-m-thick unit (IV) above ca. 49 Ma basaltic basement at International Ocean Discovery Program Site U1438 in the Amami Sankaku Basin. During deposition of Unit IV the site was located ∼250 km from the plate edge, where Izu-Bonin-Mariana subduction initiated at 52 Ma. Basement basalts are overlain by a mudstone-dominated subunit (IVC) with a thin basal layer of dark brown metalliferous mudstone followed by mudstone with sparse, graded laminae of amphibole- and biotite-bearing tuffaceous sandstone and siltstone. Amphibole and zircon ages from these laminae suggest that the intermediate subduction-related magmatism that sourced them initiated at ca. 47 Ma soon after basement formation. Overlying volcaniclastic, sandy, gravity-flow deposits (subunit IVB) have a different provenance; shallow water fauna and tachylitic glass fragments indicate a source volcanic edifice that rose above the carbonate compensation depth and may have been emergent. Basaltic andesite intervals in upper subunit IVB have textures suggesting emplacement as intrusions into unconsolidated sediment on a volcanic center with geochemical and petrological characteristics of mafic, differentiated island arc magmatism. Distinctive Hf-Nd isotope characteristics similar to the least-radiogenic Izu-Bonin-Mariana boninites support a relatively old age for the basaltic andesites similar to detrital amphibole dated at 47 Ma. The absence of boninites at that time may have resulted from the position of Site U1438 at a greater distance from the plate edge. The upper interval of mudstone with tuffaceous beds (subunit IVA) progresses upsection into Unit III, part of a wedge of sediment fed by growing arc-axis volcanoes to the east. At Site U1438, in what was to become a reararc position, the succession of early extensional basaltic magmatism associated with spontaneous subduction initiation is followed by a rapid transition into potentially widespread subduction-related magmatism and sedimentation prior to the onset of focused magmatism and major arc building.

Document Type: Article
Keywords: Subduction Initiation, IODP, Island Arc, Izu-Bonin
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS > Marine Mineralische Rohstoffe
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS
Main POF Topic: PT8: Georesources
Refereed: Yes
Open Access Journal?: No
Publisher: GSA (Geological Society of America)
Projects: IODP
Expeditions/Models/Experiments:
Date Deposited: 30 Jul 2021 11:57
Last Modified: 07 Feb 2024 15:28
URI: https://oceanrep.geomar.de/id/eprint/53643

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