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Evidence from the rare-earthelement record of mantle melting for cooling of the Tertiary Iceland plume

机译：来自罕见的地幔融化作用以冷却冰岛第三纪羽流的证据

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Widespread flood basalt volcanism and continental rifting in the northeast Atlantic in the early Tertiary period (～55 Myr ago) have been linked to the mantle plume now residing beneath Iceland. Although much is known about the present-day Iceland plume, its thermal structure, composition and position in the early Tertiary period remain unresolved. Estimates of its temperature, for example, range from >1,600℃ in some plume models to ～1,500℃ based on the volume and composition of basaltic crust. Several recent studies have emphasized similarities in the thermal and chemical structure of the Tertiary and present-day plumes to argue for stability of the mantle anomaly, whereas others relate variations in basalt volumes and compositions to changes in plume flux. Moreover, some authors have assumed that the plume was rift-centred for its entire history, whereas others argue that it became ridge-centred only after plate separation. Here we report compositional data for ～6,000 metres of flood basalts erupted in east Greenland, close to the inferred plume axis, that we use to constrain the Tertiary plume structure. Rare-earth-element systematics place limits on the pressures and extents of mantle melting and show that the mantle was initially moderately hot (～ 1,500℃), but that its temperature declined during flood volcanism. These observations are difficult to reconcile with current plume-head models, and call for important lithospheric control on actively upwelling mantle along the rifted margin.
机译：第三纪初期（〜55 Myr以前）东北大西洋东北部广泛的洪水玄武岩火山作用和大陆裂谷与现在居住在冰岛之下的地幔柱有关。尽管对当今的冰岛羽流了解很多，但其热结构，成分和在第三纪初期的位置仍未解决。例如，根据玄武岩壳的体积和成分，对某些羽状模型的温度估算范围从1600℃到1500℃不等。最近的几项研究强调了第三纪和当今羽状体的热和化学结构的相似性，以证明地幔异常的稳定性，而另一些研究则将玄武岩体积和成分的变化与羽状流的变化联系起来。此外，一些作者认为羽状流在整个历史过程中都是以裂谷为中心的，而另一些人则认为，仅在板块分离后才变为脊状中心。在这里，我们报告了在格陵兰岛东部靠近推断烟羽轴的大约6,000米洪水玄武岩的组成数据，这些数据被用来限制第三纪烟羽结构。稀土元素系统限制了地幔融化的压力和程度，表明地幔起初为中等高温（〜1,500℃），但在洪水火山爆发期间其温度下降了。这些观测值很难与当前的羽状头模型相吻合，并要求对沿裂谷边缘主动上升的地幔进行重要的岩石圈控制。

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