Deep seismic structure across the southernmost Mariana trench: Implications for arc rifting and plate hydration

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Wan, Kuiyuan
Lin, Jian
Xia, Shaohong
Sun, Jinlong
Xu, Min
Yang, Hongfeng
Zhou, Zhiyuan
Zeng, Xin
Cao, Jinghe
Xu, Huilong
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Arc rifting
Plate hydration
Southernmost Mariana Trench
Seismic tomography
The southernmost Mariana margin lacks a mature island arc and thus differs significantly from the central‐north Mariana and Izu‐Bonin margins. This paper presents a new P wave velocity model of the crust and uppermost mantle structure based on a 349‐km‐long profile of wide‐angle reflection/refraction data. The active source seismic experiment was conducted from the subducting Pacific plate to the overriding Philippine plate, passing through the Challenger Deep. The subducting plate has an average crustal thickness of ~6.0 km with Vp of 7.0 ± 0.2 km/s at the base of the crust and low values of only 5.5–6.9 km/s near the trench axis. The uppermost mantle of the subducting plate is characterized by low velocities of 7.0–7.3 km/s. The overriding plate has a maximum crustal thickness of ~18 km beneath the forearc with Vp of ~7.4 km/s at the crustal bottom and 7.5–7.8 km/s in the uppermost mantle. A zone of slight velocity reduction is imaged beneath the Southwest Mariana Rift that is undergoing active rifting. The observed significant velocity reduction in a near‐trench crustal zone of ~20–30 km in the subducting plate is interpreted as a result of faulting‐induced porosity changes and fracture‐filling fluids. The velocity reduction in the uppermost mantle of both subducting and overriding plates is interpreted as mantle serpentinization with fluid sources from dehydration of the subducting plate and/or fluid penetration along faults.
Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Solid Earth 124(5), (2019): 4710-4727, doi:10.1029/2018JB017080.
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Wan, K., Lin, J., Xia, S., Sun, J., Xu, M., Yang, H., Zhou, Z., Zeng, X., Cao, J., & Xu, H. (2019). Deep seismic structure across the southernmost Mariana trench: Implications for arc rifting and plate hydration. Journal of Geophysical Research-Solid Earth, 124(5), 4710-4727.
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