Abstract Among many Paleoproterozoic Orogens, the Birimian-Eburnean Orogeny is of a particular importance due to its vital role in connecting the African and South American blocks during the Columbia supercontinent assembly. Although, several tectonic models are proposed for the Birimian-Eburnean Orogen of West Africa, more and more studies demonstrate that the Birimian-Eburnean Orogen was dominated by arc-related accretion/collision. We present geochemical characteristics, Lu-Hf-O isotopes composition and zircon U-Pb ages of metagranites from the Dahomeyide basement of Ghana to constrain crustal thickness during the Birimian-Eburnean Orogeny. The metagranites intrude into the dominant Dahomeyide orthogneisses but are not documented. They are mainly high-K calc-alkaline, weakly peraluminous with A/CNK of 1.0–1.07. They have very high Sr/Y and (La/Yb)N, and are strongly depleted in HREE and HFSE. They exhibit potassic TTGs-like geochemical characteristics and yield zircon U-Pb ages of 2100±6–2118±30 Ma. They show subchondritic Lu-Hf isotope compositions with eHf(t) values of -11.1 to -1.6, and preserve typical I-type granitoids oxygen isotope composition with zircon δ18O of 6.4–6.7‰, quartz δ18O of 9.3–9.7‰, plagioclase δ18O of 7.4–7.8‰, K-feldspar δ18O of 7.0–7.3‰, biotite δ18O of 3.5–4.3‰, and whole-rock δ18O of 8.3–8.5‰. Comparison of data for the metagranites with data previously reported for the host orthogneisses indicate that metagranites are relatively younger but preserve Lu-Hf-O signatures similar to the orthogneisses. This suggests that both rock suites were derived from melting of common Archaean igneous rocks. However, theoretical modelling of partial melting indicates that the metagranites formed in a thickened lower crust with rutile-eclogites residue in a depth ≥50km, whereas the host orthogneisses formed in the lower crust with garnet-amphibolite residue in a depth of ≤ 35 km. This marks gradual crustal thickening as a result of arc-continent collision during the Birimian-Eburnean Orogeny. This supports modern-style plate tectonics controlled by subduction-collision as the main geodynamic mechanism operated during the Birimian-Eburnean Orogen in the background of the Columbia supercontinent assembly.

中文翻译：

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来自加纳达荷美德带的古元古代过渡型 TTG 变花岗岩：对比里米亚-埃本造山带演化的限制

摘要 在众多古元古代造山带中，Birimian-Eburnean造山带因其在哥伦比亚超大陆组装期间连接非洲和南美地块的重要作用而具有特别重要的意义。尽管西非的比里米安-埃本造山带提出了几种构造模型，但越来越多的研究表明，比里米安-埃本尼造山带以弧相关的吸积/碰撞为主。我们介绍了来自加纳达荷美德基底的变花岗岩的地球化学特征、Lu-Hf-O 同位素组成和锆石 U-Pb 年龄，以限制 Birimian-Eburnean 造山运动期间的地壳厚度。变花岗岩侵入占主导地位的达荷美德正片麻岩，但没有记录。它们主要是高钾钙碱性，弱过铝，A/CNK 为 1.0-1.07。它们具有非常高的 Sr/Y 和 (La/Yb)N，并且严重耗尽 HREE 和 HFSE。它们表现出类似钾 TTG 的地球化学特征，锆石 U-Pb 年龄为 2100±6–2118±30 Ma。它们显示了球粒下 Lu-Hf 同位素组成，eHf(t) 值为 -11.1 至 -1.6，并保留了典型的 I 型花岗岩氧同位素组成，其中锆石 δ18O 为 6.4-6.7‰，石英 δ18O 为 9.3-9.7‰，斜长石为 δ18O 7.4-7.8‰，钾长石δ18O 7.0-7.3‰，黑云母δ18O 3.5-4.3‰，全岩δ18O 8.3-8.5‰。变花岗岩数据与先前报道的寄主正片麻岩数据的比较表明，变花岗岩相对较年轻，但保留了类似于正片麻岩的 Lu-Hf-O 特征。这表明这两个岩石套件都来自普通太古代火成岩的熔化。然而，部分熔融的理论模型表明变花岗岩形成于加厚的下地壳，金红石-榴辉岩残留深度≥50km，而寄主正片麻岩形成于下地壳，石榴石-角闪岩残留深度≤35km。这标志着由于比里米安-埃本尼造山运动期间弧-大陆碰撞导致地壳逐渐增厚。这支持了由俯冲碰撞控制的现代板块构造，作为在哥伦比亚超大陆组装背景下的比里米安-埃本造山带期间运行的主要地球动力学机制。这标志着由于比里米安-埃本尼造山运动期间弧-大陆碰撞导致地壳逐渐增厚。这支持了由俯冲碰撞控制的现代板块构造，作为在哥伦比亚超大陆组装背景下的比里米安-埃本造山带期间运行的主要地球动力学机制。这标志着由于比里米安-埃本尼造山运动期间弧-大陆碰撞导致地壳逐渐增厚。这支持了由俯冲碰撞控制的现代板块构造，作为在哥伦比亚超大陆组装背景下的比里米安-埃本造山带期间运行的主要地球动力学机制。