Highly heterogeneous depleted mantle recorded in the lower oceanic crust
Highly heterogeneous depleted mantle recorded in the lower oceanic crust
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DOI：
10.1038/s41561-019-0368-9
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发表时间：
2019-05
影响因子：
18.3
通讯作者：
S. Lambart;J. Koornneef;M. Millet;G. Davies;M. Cook;C. Lissenberg
中科院分区：
文献类型：
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作者：
S. Lambart;J. Koornneef;M. Millet;G. Davies;M. Cook;C. Lissenberg
地球的地幔是不均匀的，这是早期行星分异和随后板块构造期间地壳再循环的结果。几十年来，洋中脊玄武岩的放射性同位素特征一直被用来绘制地幔成分图，确定亏损的地幔端元。然而，这些熔岩通过岩浆混合而均匀化，可能无法捕获其地幔源的全部化学变化。在这里，我们表明，亏损地幔是显着的异质性比以前推断的熔岩在表面的组合物，延伸到高度富集的组合物。我们进行高空间分辨率的单斜辉石和斜长石的同位素分析，从下地壳辉长岩钻孔上耗尽脊段的北方大西洋中脊。这些原始堆积矿物几乎记录了沿北方中大西洋海岭（包括热点）沿着观察到的全部不均匀性。我们的研究结果表明，大量的地幔不均匀性隐藏在下洋壳和熔融来自不同的地幔成分可以传递到下地壳厘米尺度。这些发现为重新评价板块再循环、地幔对流以及地幔和地壳中的熔体输运模型提供了一个起点。
The Earth’s mantle is heterogeneous as a result of early planetary differentiation and subsequent crustal recycling during plate tectonics. Radiogenic isotope signatures of mid-ocean ridge basalts have been used for decades to map mantle composition, defining the depleted mantle endmember. These lavas, however, homogenize via magma mixing and may not capture the full chemical variability of their mantle source. Here, we show that the depleted mantle is significantly more heterogeneous than previously inferred from the compositions of lavas at the surface, extending to highly enriched compositions. We perform high-spatial-resolution isotopic analyses on clinopyroxene and plagioclase from lower crustal gabbros drilled on a depleted ridge segment of the northern Mid-Atlantic Ridge. These primitive cumulate minerals record nearly the full heterogeneity observed along the northern Mid-Atlantic Ridge, including hotspots. Our results demonstrate that substantial mantle heterogeneity is concealed in the lower oceanic crust and that melts derived from distinct mantle components can be delivered to the lower crust on a centimetre scale. These findings provide a starting point for re-evaluation of models of plate recycling, mantle convection and melt transport in the mantle and the crust.