Eu is the most concerned variable valence rare earth element (Eu, Eu2+ and Eu3+) in the geological science. For a long time, "Eu anomaly" (δEu) has been widely used as an important geochemical parameter to finely characterize geological processes. It is generally believed that the existence and stability of Eu2+ in natural environments are the main causes of "Eu anomaly". However, recent literatures have shown that many explanations for the cause of "Eu anomaly" are vague and even contradictory. On the basis of the definition and calculation formula of "Eu anomaly", this article summarizes the application status of Eu anomaly and related experimental geochemical results in different geological processes, including magma evolution, hydrothermal action, sedimentation, metamorphism and weathering. Comprehensive research shows that the main factors causing "Eu anomaly" in different geological processes are summarized as follows: (1) Eu content in parent magma (melt/fluid); (2) crystallization chemistry effects (ionic radius) of different mineral phases; (3) temperature-pressure; (4) oxidation-reduction conditions (oxygen, sulfur fugacity); (5) water-rock interaction; (6) fluid acidity and alkalinity (pH value); (7) complexation; (8) adsorption; (9) weathering; and (10) nebular condensation and volatilization, etc. Quantitative expression and application of "Eu anomaly" involves the precise determination of Eu2+ and Eu3+ in magma, melt/fluid or minerals. However, looking at many testing methods currently applied in Earth science, there is still a lack of feasible methods for accurately determining the content of Eu2+ and Eu3+ in the research objects, except for X-ray absorption spectroscopy (XAS) which can determine the relative content of Eu2+ and Eu3+ in situ. Therefore, experimental geochemistry presents a new method to solve the problem of "Eu anomaly". Simulation of important geological processes using melt/fluid with known Eu2+ and Eu3+ contents can effectively reveal the key limiting factors of "Eu anomaly" changes.
铕异常在地质学中的应用<稀土元素的意义是什么>
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