The magmatic complex along the Marsa Alam-Idfu transect, Central-Eastern Desert of Egypt, represents the northern segment of the Arabian–Nubian Shield (ANS), which developed within the framework of the East African Orogen. The basement rocks of the Arabian-Nubian Shield have been developed through three distinct phases of magmatic activity: the island-arc, the syn-orogenic, and the post-orogenic phases. Transitioning of the magmatic phases from the syn-orogenic to the post-orogenic, identifies changing the tectonic regime from a compressional to an extensional setting. The scarcity of comprehensive regional geochronological data that rely on precise isochron methods, such as the zircon U-Pb technique, could limit the comprehensive understanding of this region’s geological and tectonic history. That would raise a number of uncertainties ranging from the timing of the different magmatic activities and timing of changes in the tectonic regime to the existence of the pre-Pan-African crust in the CED. Our study provides new insights into the aforementioned uncertainties through zircon U-Pb dating of different rock units along the Marsa Alam-Idfu transect, CED, Egypt. The resulting ages ranged from 729 ± 3 Ma to 570 ± 2 Ma, constraining the temporal evolution of the ANS in the studied region into (1) the island-arc phase, represented by a metamorphic sample with an age of 729 ± 3 Ma. (2) the syn-orogenic phase, represented by calc-alkaline and alkaline granitic samples with ages ranging from 699 ± 4 Ma to 646 ± 2 Ma. These two phases indicate initiation of the compressional subduction regime in the CED since 729 ± 3 Ma and being dominated till 646 ± 2 Ma. (3) the post-orogenic phase, represented by metavolcanics, volcanic rocks, and alkaline plutonic samples with ages ranging from 623 ± 3 Ma to 570 ± 2 Ma. This phase suggests dominance of the compressional-to-extensional tectonic transition setting from 623 ± 3 Ma to 600 ± 1 Ma along with the Dokhan volcanism and activation of post-collision tensional regime activated at 582 ± 3 Ma. Our findings discourage the proposed dominance of the island-arc and syn-orogenic phases in the CED and the classical restriction of older magmatic activity to calc-alkaline granitic rocks and younger magmatic activity to alkaline granitic rocks. Additionally, we identified evidence of local magmatic sources by dating five grains with Mesoproterozoic (pre-Arabian–Nubian Shield) xenocrysts with ages ranging from 1549 ± 4 to 1095 ± 25 Ma.

中文翻译：

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埃及中东沙漠 Marsa Alam-Idfu 样带沿阿拉伯-努比亚地盾的开发：锆石 U-Pb 地质年代学的地球化学实施


埃及中东部沙漠沿 Marsa Alam-Idfu 横断面的岩浆复合体代表了阿拉伯-努比亚地盾 （ANS） 的北段，该地盾是在东非造山带的框架内发展起来的。阿拉伯-努比亚地盾的基岩经历了岩浆活动的三个不同阶段：岛弧、同造山阶段和造山后阶段。岩浆相从同造山期过渡到后造山期，确定了构造状态从压缩到伸展环境的变化。依赖于精确等时方法（例如锆石 U-Pb 技术）的综合区域地质年代学数据的稀缺可能会限制对该地区地质和构造历史的全面理解。这将带来许多不确定性，从不同岩浆活动的时间和构造状况变化的时间，到 CED 中泛非前地壳的存在。我们的研究通过对埃及 CED Marsa Alam-Idfu 样带沿线不同岩石单元的锆石 U-Pb 测年为上述不确定性提供了新的见解。由此产生的年龄范围从 729 ± 3 马到 570 ± 2 马，将研究区域中 ANS 的时间演变限制为 （1） 岛弧期，由年龄为 729 ± 3 马的变质样本表示。（2） 同造山阶段，以钙碱性和碱性花岗岩样品为代表，年龄从 699 ± 4 马 到 646 ± 2 马不等。这两个阶段表明自 729 ± 3 马 开始在 CED 中开始压缩俯冲状态，并一直主导到 646 ± 2 马。 （3） 后造山阶段，以变质火山岩、火山岩和碱性深成岩样品为代表，年龄从 623 ± 3 马 到 570 ± 2 马 不等。这个阶段表明，从 623 ± 3 马到 600 ± 1 马的压缩到伸展构造过渡设置占主导地位，同时 Dokhan 火山活动和碰撞后张力机制的激活在 582 ± 3 马激活。我们的研究结果不鼓励 CED 中岛弧和同造山相的主导地位，以及将较旧的岩浆活动限制在钙碱性花岗岩和较年轻的岩浆活动限制在碱性花岗岩的传统限制。此外，我们还通过用年龄从 1549 ± 4 到 1095 ± 25 马的中元古代（前阿拉伯-努比亚盾）异晶测定五粒矿物，确定了当地岩浆来源的证据。