美国拉斯维加斯大学Kevin Konrad团队的一项最新研究发现，上新世期间，汤加板块周围的环形流移动了萨摩亚地幔柱。2024年1月3日出版的《地质学》杂志发表了这项成果。

研究人员对萨摩亚热点轨迹的年龄变化和几何形状进行了探究，以从海山的深层侧翼挖掘的熔岩流样本为重点，以便最好地重建给定海山何时覆盖地幔柱(即在地盾建造阶段)。萨摩亚海山在0-9百万年的表观局部板块速度为7.8 cm/yr，9-14百万年为11.1 cm/yr，14-24百万年为5.6 cm/yr。如果假定热点位置长期固定，目前位于活跃的Vailulu’u海山之下，则目前的固定和移动热点太平洋APM模型无法再现萨摩亚海山轨迹的几何形状。

利用APM模式对萨摩亚海山喷发位置的重建表明，在上新世，地幔柱的表明表现向北迁移了约2°。太平洋盆地下的大规模地幔流无法解释这种地幔柱迁移。相反，最好的解释是，环形流（由汤加海沟的向西迁移和相关板块的后退产生）在过去的2-3m.y.里使得通道向北偏转。这些观测结果提供为地幔柱—海沟相互作用改变热点轨迹的方式提供了新的约束方式。

据介绍，由静止地幔柱上岩石圈运动产生的年龄递增的海山轨迹，长期以来被用于重建绝对板块运动(APM)模型。然而，这些模型的基础要求为地幔柱的移动速度要明显慢于上覆的岩石圈。当地幔柱与汇聚或发散的板块边界相互作用时，通常会在与这些状态相关的强局部地幔流场中发生偏转。

附：英文原文

Title: Toroidal flow around the Tonga slab moved the Samoan plume during the Pliocene

Author: Kevin Konrad, Matthew Jackson, Bernhard Steinberger, Anthony Koppers, Andrea Balbas, Valerie Finlayson, Jasper Konter, Allison Price

Issue&Volume: 2024-01-03

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 23 m.y. These observations provide novel constraints on the ways in which plume-trench interactions can alter hotspot track geometries.

DOI: 10.1130/G51588.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G51588.1/632076/Toroidal-flow-around-the-Tonga-slab-moved-theredirectedFrom=fulltext