Ubiquitous ultra-depleted domains in Earth’s mantle
Ubiquitous ultra-depleted domains in Earth’s mantle
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DOI：
10.1038/s41561-019-0446-z
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发表时间：
2019-09
影响因子：
18.3
通讯作者：
A. Stracke;F. Genske;J. Berndt;J. Koornneef
中科院分区：
文献类型：
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作者：
A. Stracke;F. Genske;J. Berndt;J. Koornneef
地幔的部分熔融产生了海洋地壳，留下了化学物质耗尽的残余地幔。这种化学耗尽的地幔的时间积分组成通常是从大洋中脊产生的玄武岩中推断出来的。然而，海洋地幔岩和洋中脊玄武岩之间的同位素差异表明，地幔和玄武岩的组成可能不同。在这里，我们测量了亚速尔群岛地幔柱熔岩中含有橄榄石的熔融包裹体的钕同位素比率。我们发现在玄武岩中测量到的钕同位素比值最高，并表明来自超贫地幔的熔体有助于喷发熔岩的同位素多样性。在岩浆提取和演化过程中，超贫熔体与富含不相容元素的熔体不断混合，保存潜力极低。因此，亚速尔群岛地幔柱中超贫熔融体的显著贡献表明，变贫地幔在体积上是亚速尔群岛地幔柱的主要组成部分。我们认为，变贫地幔，有时范围到超贫成分，可能是大多数海洋岛屿和洋中脊玄武岩源的普遍组成部分。如果是这样，地幔可能比以前认为的更枯竭，这对地壳和地幔之间的物质交换速率、地幔的羽流动力学和地幔的成分分层具有重要意义。
Partial melting of Earth’s mantle generates oceanic crust and leaves behind a chemically depleted residual mantle. The time-integrated composition of this chemically depleted mantle is generally inferred from basalts produced at mid-ocean ridges. However, isotopic differences between oceanic mantle rocks and mid-ocean ridge basalts suggest that mantle and basalt composition could differ. Here we measure neodymium isotope ratios in olivine-hosted melt inclusions from lavas of the Azores mantle plume. We find neodymium isotope ratios that include the highest values measured in basalts, and suggest that melts from ultra-depleted mantle contribute to the isotopic diversity of the erupted lavas. Ultra-depleted melts have exceedingly low preservation potential during magma extraction and evolution due to progressive mixing with melts that are enriched in incompatible elements. A notable contribution of ultra-depleted melts to the Azores mantle plume therefore implies that variably depleted mantle is the volumetrically dominant component of the Azores plume. We argue that variably depleted mantle, sometimes ranging to ultra-depleted compositions, may be a ubiquitous part of most ocean island and mid-ocean ridge basalt sources. If so, Earth’s mantle may be more depleted than previously thought, which has important implications for the rate of mass exchange between crust and mantle, plume dynamics and compositional stratification of Earth’s mantle.