Abstract This study presents petrography, geochemistry, geochronology, and Lu-Hf isotope compositions of Paleoproterozoic orthogneisses from the Dahomeyide Belt, southeastern Ghana. Previous studies indicated that these rocks represent part of the Birimian of the West African Craton, remobilized during the Pan-African Orogen. The results obtained from this study indicate that the Dahomeyide basement are mainly amphibole and biotite orthogneisses of medium-K, tonalitic composition, and biotite and muscovite bearing orthogneisses of high-K granodioritic composition. Both suites are mainly magnesian, calc-alkaline, metaluminous to weak peraluminous with A/CNK values of 0.86 – 1.03. They are rich in LREEs, LILEs and heat-producing elements (Ba, K, Pb, and Sr). They are moderately rich in V and Zn and show variable (La/Yb)N and Sr/Y ratios with geochemical characteristics akin to the Neoarchaean sanukitoids. However, they are depleted in Ni and Cr relative to the sanukitoids. Zircon U-Pb ages determined on two amphibole-biotite and four biotite-muscovite orthogneisses yield 2145 ± 12 Ma – 2122 ± 27 Ma and 2105 ± 18 – 2125 ± 25 Ma respectively. The amphibole-biotite orthogneisses show eHf(∼2.1Ga) values of -9.5 to -3.7, pointing to mean model ages of (TDM1) of 2721 ± 24 – 2761 ± 14 Ma and T(DM2) of 3053 ± 26 – 3125 ± 25 Ma. Similarly, the biotite and muscovite orthogneisses present eHf(∼2.1Ga) values of -10.6 to -1.7, corresponding to mean T(DM1) of 2743 ± 14 – 2733 ± 20 Ma and mean T(DM2) of 2949 ± 26 – 3111 ± 36 Ma. The data suggest that the Dahomeyide basement rocks are derived mainly from partial melting of Neoarchaean lower crust and sediments with little or no mantle contribution. A collision between Birimian arc and an unknown Archaean crust (possibly, now the Dahomeyide Belt) accounted for the formation of these rocks. This study provides first data on the evidence of reworked Archaean crust in the Pan-African Dahomeyide Belt along the eastern border of the West African Craton. Our data serves as comprehensive evidence supporting older crustal contribution in the geodynamic evolution of the juvenile Eburnean/Birimian crust of the West African Craton.

中文翻译：

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对西非加纳东南部达荷美德带的新见解：弧-大陆碰撞和新太古代地壳改造的证据

摘要 本研究介绍了加纳东南部达荷伊德带古元古代正片麻岩的岩石学、地球化学、年代学和 Lu-Hf 同位素组成。先前的研究表明，这些岩石代表了西非克拉通比里米亚层的一部分，在泛非造山带期间重新活动。本次研究结果表明，达荷美德基底主要为中K、斜长岩组成的角闪石和黑云母正方麻岩，以及含高K花岗闪长岩的黑云母和白云母正方麻岩。两个套件主要是镁质、钙碱性、金属铝至弱过铝质，A/CNK 值为 0.86 – 1.03。它们富含 LREE、LILE 和发热元素（Ba、K、Pb 和 Sr）。它们富含 V 和 Zn，并显示出可变的 (La/Yb)N 和 Sr/Y 比率，具有类似于新太古代 sanukitoids 的地球化学特征。然而，它们相对于 sanukitoids 缺乏 Ni 和 Cr。在两个角闪石-黑云母和四个黑云母-白云母正片麻岩上确定的锆石 U-Pb 年龄分别为 2145 ± 12 Ma – 2122 ± 27 Ma 和 2105 ± 18 – 2125 ± 25 Ma。角闪石-黑云母正方麻岩显示 eHf(∼2.1Ga) 值为 -9.5 至 -3.7，表明 (TDM1) 的平均模型年龄为 2721 ± 24 – 2761 ± 14 Ma 和 T(DM2) 为 3053 ± 26 – 3125 ± 25 马。同样，黑云母和白云母正片麻岩的 eHf(∼2.1Ga) 值为 -10.6 至 -1.7，对应于 2743 ± 14 – 2733 ± 20 Ma 的平均 T(DM1) 和 2949 ± 26 – 3111 的平均 T(DM2) ± 36 毫安。资料表明，达荷美德基岩主要来源于新太古代下地壳和沉积物的部分熔融，地幔贡献很小或没有。Birimian 弧与未知的太古代地壳（可能是现在的达荷美德带）之间的碰撞导致了这些岩石的形成。这项研究提供了关于沿西非克拉通东部边界的泛非达荷美德带中再造太古代地壳证据的第一个数据。我们的数据作为综合证据支持旧地壳对西非克拉通幼年埃本/比里米亚地壳地球动力学演化的贡献。现在达荷伊德带）解释了这些岩石的形成。这项研究提供了关于沿西非克拉通东部边界的泛非达荷美德带中再造太古代地壳证据的第一个数据。我们的数据作为综合证据支持旧地壳对西非克拉通幼年埃本/比里米亚地壳地球动力学演化的贡献。现在达荷伊德带）解释了这些岩石的形成。这项研究提供了关于沿西非克拉通东部边界的泛非达荷美德带中再造太古代地壳证据的第一个数据。我们的数据作为综合证据支持旧地壳对西非克拉通幼年埃本/比里米亚地壳地球动力学演化的贡献。