The Neoproterozoic Bure adakitic rock in the western Ethiopia shield is a newly discovered magmatic rock type. However, the physicochemical conditions during its formation, and its source characteristics are still not clear, restricting a full understanding of its petrogenesis and geodynamic evolution. In this study, in order to shed light on the physicochemical conditions during rock formation and provide further constraints on the petrogenesis of the Bure adakitic rock, we conduct electron microprobe analysis on K-feldspar, plagioclase, and biotite. Additionally, we investigate the trace elements and Hf isotopes of zircon, and the Sr-Nd isotopes of the whole rock. The results show that the K-feldspar is orthoclase (Or = 89.08~96.37), the plagioclase is oligoclase (Ab = 74.63~85.99), and the biotite is magnesio-biotite. Based on the biotite analysis results, we calculate that the pressure during rock formation was 1.75~2.81 kbar (average value of 2.09 kbar), representing a depth of approximately 6.39~10.2 km (average value of 7.60 km). The zircon thermometer yields a crystallization temperature of 659~814 °C. Most of the (Ce/Ce*)D values in the zircons plotted above the Ni-NiO oxygen buffer pair, and the calculated magmatic oxygen fugacity (logfO2) values vary from −18.5 to −4.9, revealing a relatively high magma oxygen fugacity. The uniform contents of FeO, MgO, and K2O in the biotite suggest a crustal magma source for the Bure adakitic rock. The relatively low (87Sr/86Sr)i values of 0.70088 to 0.70275, positive εNd(t) values of 3.26 to 7.28, together with the positive εHf(t) values of 7.64~12.99, suggest that the magma was sourced from a Neoproterozoic juvenile crust, with no discernable involvement of a pre-Neoproterozoic continental crust, which is coeval with early magmatic stages in the Arabian Nubian Shield elsewhere. Additionally, the mean Nd model ages demonstrate an increasing trend from the northern parts (Egypt, Sudan, Afif terrane of Arabia, and Eritrea and northern Ethiopia; 0.87 Ga) to the central parts (Western Ethiopia shield; 1.03 Ga) and southern parts (Southern Ethiopia Shield, 1.13 Ga; Kenya, 1.2 Ga) of the East African Orogen, which indicate an increasing contribution of pre-Pan-African crust towards the southern part of the East African Orogen. Based on the negative correlation between MgO and Al2O3 in the biotite, together with the Lu/Hf-Y and Yb-Y results of the zircon, we infer that the Bure adakitic rock was formed in an arc–arc collision orogenic environment. Combining this inference with the whole rock geochemistry and U-Pb age of the Bure adakitic rock, we further propose that the rock is the product of thickened juvenile crust melting triggered by the Neoproterozoic Pan-African Orogeny.

中文翻译：

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埃塞俄比亚地盾西部布雷地区新发现的新元古代埃达克岩的岩石成因：对泛非构造演化的启示

埃塞俄比亚地盾西部新元古代布雷埃达克岩是新发现的岩浆岩类型。然而，其形成过程的物理化学条件和物源特征仍不清楚，限制了对其岩石成因和地球动力学演化的全面认识。在本研究中，为了揭示岩石形成过程中的物理化学条件，并为Bure埃达克岩的岩石成因提供进一步的约束，我们对钾长石、斜长石和黑云母进行了电子探针分析。此外，我们还研究了锆石的微量元素和Hf同位素，以及整个岩石的Sr-Nd同位素。结果表明，钾长石为正长石（Or = 89.08~96.37），斜长石为寡长石（Ab = 74.63~85.99），黑云母为镁黑云母。根据黑云母分析结果，我们计算出岩石形成时的压力为1.75~2.81 kbar（平均值为2.09 kbar），深度约为6.39~10.2 km（平均值为7.60 km）。锆石温度计测得结晶温度为659~814℃。锆石中的大多数 (Ce/Ce*)D 值绘制在 Ni-NiO 氧缓冲对上方，计算出的岩浆氧逸度 (logfO2) 值在 -18.5 至 -4.9 之间变化，揭示了相对较高的岩浆氧逸度。黑云母中 FeO、MgO 和 K2O 的均匀含量表明 Bure 埃达克岩的地壳岩浆来源。相对较低的 (87Sr/86Sr)i 值为 0.70088 至 0.70275，正 εNd(t) 值为 3.26 至 7.28，正 εHf(t) 值为 7.64~12.99，表明岩浆来自新元古代幼体。地壳，没有明显的前新元古代大陆地壳的参与，这与其他地方的阿拉伯努比亚地盾的早期岩浆阶段是同时期的。此外，平均 Nd 模型年龄表现出从北部（埃及、苏丹、阿拉伯阿菲夫地体、厄立特里亚和埃塞俄比亚北部；0.87 Ga）到中部（埃塞俄比亚西部地盾；1.03 Ga）和南部（东非造山带的埃塞俄比亚南部地盾，1.13 Ga；肯尼亚，1.2 Ga），这表明前泛非地壳对东非造山带南部的贡献不断增加。根据黑云母中MgO和Al2O3的负相关关系，结合锆石的Lu/Hf-Y和Yb-Y结果，我们推断布尔埃达克岩形成于弧-弧碰撞造山环境中。结合这一推论与整个岩石地球化学和Bure埃达克岩的U-Pb年龄，我们进一步提出该岩石是新元古代泛非造山运动引发的增厚的新生地壳熔融的产物。