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.

中文翻译：

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上新世期间，汤加板块周围的环形流移动了萨摩亚羽流

由静止地幔柱上的岩石圈运动产生的年龄渐进海山轨迹长期以来一直被用来重建绝对板块运动（APM）模型。然而，这些模型的基础要求羽流的移动速度明显慢于覆盖岩石圈的速度。当羽流与会聚或发散的板块边界相互作用时，它通常会在与此类区域相关的强局部地幔流场内发生偏转。在这里，我们研究了萨摩亚热点轨迹的年龄进程和几何形状，重点关注从海山深侧挖出的熔岩流样本，以便在给定海山覆盖地幔柱时（即在盾构建造阶段）进行最佳重建）。萨摩亚海山显示，0至9Ma期间的局部板块视速度为7.8厘米/年，9至14Ma期间为11.1厘米/年，14至24Ma期间为5.6厘米/年。如果假设长期固定热点位置目前位于活跃的瓦卢卢乌海山下方，则当前的固定和移动热点太平洋 APM 模型无法重现萨摩亚海山轨道的几何形状。相反，使用 APM 模型重建萨摩亚海山喷发位置表明，羽流的表面表达在上新世向北迁移了约 2°。太平洋盆地下方的大规模地幔流无法解释这种羽流迁移。相反，最好的解释是，由汤加海沟向西迁移和相关板片回滚产生的环形流场在过去 2-3 年内使管道向北偏转。这些观察结果为羽流与海沟相互作用的方式提供了新的限制。可以改变热点轨道的几何形状。