New K-Ar ages, major and trace element concentrations, and Sr-Nd-Pb isotope data are presented for Oligocene to recent mafic volcanic rocks from the Ethiopian Plateau, the Main Ethiopian Rift (MER), and the Afar depression. Chronological and geochemical data from this study are combined with previously published datasets to reveal secular variations in magmatism throughout the entire Ethiopian volcanic region. The mafic lavas in these regions show variability in terms of silica-saturation (i.e. alkaline and sub-alkaline series) and extent of differentiation (mafic through intermediate to felsic). The P-T conditions of melting, estimated using the least differentiated basalts, reveal a secular decrease in the mantle potential temperature, from when the flood basalt magmas erupted (up to 1600 degrees C) to the time of the rift-related magmatism (<1500 degrees C). Variations in the Sr-Nd-Pb isotopic compositions of the mafic lavas can account for the involvement of multiple end-member components. The relative contributions of these end-member components vary in space and time owing to changes in the thermal condition of the asthenosphere and the thickness of the lithosphere. The evolution of the Ethiopian rift is caused by a transition from plume-driven to plate-driven mantle upwelling, although the present-day mantle beneath the MER and the Afar depression is still warmer than normal asthenosphere.

中文翻译：

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埃塞俄比亚主裂谷演化过程中从羽流驱动向板块驱动岩浆作用的转变

新的 K-Ar 年龄、主要和微量元素浓度以及 Sr-Nd-Pb 同位素数据提供了渐新世到最近来自埃塞俄比亚高原、埃塞俄比亚主裂谷 (MER) 和阿法尔洼地的基性火山岩。这项研究的年代学和地球化学数据与之前发布的数据集相结合，揭示了整个埃塞俄比亚火山区岩浆活动的长期变化。这些地区的镁铁质熔岩在二氧化硅饱和度（即碱性和亚碱性系列）和分化程度（镁铁质到中长英质到长英质）方面表现出变异性。使用差异最小的玄武岩估计的 PT 熔化条件表明，从泛滥玄武岩岩浆喷发时（高达 1600 摄氏度）到与裂谷相关的岩浆活动发生时（< 1500 摄氏度）。镁铁质熔岩的 Sr-Nd-Pb 同位素组成的变化可以解释多种端元组分的参与。由于软流圈热条件和岩石圈厚度的变化，这些端元组分的相对贡献在空间和时间上发生变化。埃塞俄比亚裂谷的演化是由从羽流驱动到板块驱动的地幔上涌的转变造成的，尽管现今 MER 和阿法尔坳陷下方的地幔仍然比正常软流圈温暖。由于软流圈热条件和岩石圈厚度的变化，这些端元组分的相对贡献在空间和时间上发生变化。埃塞俄比亚裂谷的演化是由从羽流驱动到板块驱动的地幔上涌的转变造成的，尽管现今 MER 和阿法尔坳陷下方的地幔仍然比正常软流圈温暖。由于软流圈热条件和岩石圈厚度的变化，这些端元组分的相对贡献在空间和时间上会发生变化。埃塞俄比亚裂谷的演化是由从羽流驱动到板块驱动的地幔上涌的转变造成的，尽管现今 MER 和阿法尔坳陷下方的地幔仍然比正常软流圈温暖。