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Abstract Age-progressive seamount tracks generated by lithospheric motion over a stationary mantle plume have long been used to reconstruct absolute plate motion (APM) models. However, the basis of these models requires the plumes to move significantly slower than the overriding lithosphere. When a plume interacts with a convergent or divergent plate boundary, it is often deflected within the strong local mantle flow fields associated with such regimes. Here, we examined the age progression and geometry of the Samoa hotspot track, focusing on lava flow samples dredged from the deep flanks of seamounts in order to best reconstruct when a given seamount was overlying the mantle plume (i.e., during the shield-building stage). The Samoan seamounts display an apparent local plate velocity of 7.8 cm/yr from 0 to 9 Ma, 11.1 cm/yr from 9 to 14 Ma, and 5.6 cm/yr from 14 to 24 Ma. Current fixed and mobile hotspot Pacific APM models cannot reproduce the geometry of the Samoa seamount track if a long-term fixed hotspot location, currently beneath the active Vailulu’u Seamount, is assumed. Rather, reconstruction of the eruptive locations of the Samoan seamounts using APM models indicates that the surface expression of the plume migrated ~2° northward in the Pliocene. Large-scale mantle flow beneath the Pacific Ocean Basin cannot explain this plume migration. Instead, the best explanation is that toroidal flow fields—generated by westward migration of the Tonga Trench and associated slab rollback—have deflected the conduit northward over the past 2–3 m.y. These observations provide novel constraints on the ways in which plume-trench interactions can alter hotspot track geometries.
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Seismic Evidence for Plume‐Slab Interaction by High‐Resolution Imaging of the 410‐km Discontinuity Under Tonga
Abstract The Tonga‐Samoa system provides a unique tectonic context to study how a cold subducting slab interacts with a hot rising mantle plume. Here we present a 3‐D high‐resolution image of the 410‐km mantle discontinuity (the410) using seismic signals excited by deep‐focus earthquakes. The410is found to be ~30 km shallower inside the Tonga slab relative to the ambient mantle and ~20 km deeper further to the northwest under Fiji Islands. The downward deflection of the410under Fiji supports the hypothesis of a plume migration around the northern edge of the Tonga slab from Samoan hot spot to under Fiji due to fast trench rollback. The 50‐km topography difference in the410between the plume and the slab corresponds to a temperature difference of ~500 ± 100 K. The Samoan plume is inferred to be 200 ± 50 K hotter than the ambient mantle and supports a thermal origin for the plume.
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- Award ID(s):
- 1848327
- PAR ID:
- 10373078
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 46
- Issue:
- 23
- ISSN:
- 0094-8276
- Page Range / eLocation ID:
- p. 13687-13694
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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