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首页> 外文期刊>Chinese science bulletin >Old EMI-type enriched mantle under the middle North China Craton as indicated by Sr and Nd isotopes of mantle xenoliths from Yangyuan, Hebei Province
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Old EMI-type enriched mantle under the middle North China Craton as indicated by Sr and Nd isotopes of mantle xenoliths from Yangyuan, Hebei Province

机译：华北克拉通中部的旧EMI型富集地幔，如河北阳源地幔异岩的Sr和Nd同位素所示

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摘要

Mantle xenoliths hosted in Tertiary alkali basalts in Yangyuan, Hebei Province, located to the west of the Taihangshan gravity lineament, include Iherzolites, harzburgites and pyroxenite. In the plot of olivine mode vs Fo, most of the Yangyuan peridotites deviate from the oceanic trend, falling within the fields of Archean and Proterozoic mantles. Some LREE-enriched samples exhibit EMI-type isotopic signature with epsilon_(Nd) ranging from -6.9 to -10.6 and ~(87)Sr/~(86)Sr from 0.7044 to 0.7047. By contrast, another LREE-en-riched sample has a positive epsilon_(Nd) (+5.7) similar to that for LREE-depleted peridotites. This observation suggests that the upper mantle beneath Yangyuan underwent a multi-stage metasomatism. Given the fact that EMI-type isotopic signature is usually observed in the lithosphere mantle underneath ancient cratons, the isotopic composition of the Yangyuan xenoliths provides new evidence for the existence of the old lithosphere mantle beneath western North China.
机译：位于太行山重力线西侧的河北省阳原市的三级碱性玄武岩中的地幔异岩包括Iherzolites，harzburgite和pyrxenite。在橄榄石模式与Fo的情节中，大部分阳远橄榄岩都偏离了海洋趋势，属于太古代和元古代的地幔范围内。一些富含LREE的样品表现出EMI型同位素特征，ε（Nd）介于-6.9至-10.6，〜（87）Sr /〜（86）Sr从0.7044至0.7047。相比之下，另一个富含LREE的样品的正epsilon_（Nd）（+5.7）与耗尽LREE的橄榄岩类似。该观察结果表明阳原之下的上地幔经历了多阶段交代作用。鉴于通常在古代克拉通下面的岩石圈地幔中观察到EMI型同位素特征这一事实，阳源异岩的同位素组成提供了华北西部旧岩石圈地幔存在的新证据。

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