ABSTRACT The Wa-Lawra Belt which is situated in the northern part of Ghana consists of Paleoproterozoic Birimian fine metasedimentary rocks metamorphosed to greenschist facies, particularly, in the western part. A whole-rock geochemical study of these metasedimentary rocks was undertaken to unravel their source area weathering, provenance and tectonic setting. Geochemical characteristics of the studied shales show that they are immature in nature and first cycle in origin, with little or no recycled component. Compared to Post-Archaean Australian Shales (PAAS), the studied shales indicate reduction in Zr, Hf, La, Nb, Th and Ta being the high field strength elements and evidences of transition metal enrichments in V, Ni, Sc, Co, and Cr. Major element geochemistry indicates that the shales were subjected to slight potassium metasomatism after deposition. Pre-metasomatized Chemical Index of Alteration calculations indicates that weak to moderate degree of chemical weathering took place at the sediment source area. Co-Th-La-Sc systematics reveals a combination of mafic and felsic provenances for the shales. Eu/Eu* together with values of Th/U and some abundances of trace elements show that the shales were mainly derived from juvenile rocks. Average REE model calculations suggest that the source materials are composed of about 49% basalt, 16% TTG and 35% granite.

中文翻译：

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西非克拉通东南缘古元古代 (~2.1 Ga) Wa-Lawra 带变质沉积岩物源和源区风化的地球化学约束

摘要 位于加纳北部的 Wa-Lawra 带由变质为绿片岩相的古元古代 Birimian 细变沉积岩组成，特别是在西部。对这些变沉积岩进行了全岩地球化学研究，以揭示其源区风化、来源和构造环境。所研究页岩的地球化学特征表明，其性质不成熟，成因第一次循环，很少或没有回收成分。与后太古代澳大利亚页岩 (PAAS) 相比，研究的页岩表明 Zr、Hf、La、Nb、Th 和 Ta 的减少是高场强元素和过渡金属富集 V、Ni、Sc、Co 和铬。主要元素地球化学表明，沉积后页岩经历了轻微的钾交代作用。Pre-metasomatized Chemical Index of Alteration 计算表明在沉积物源区发生了弱到中等程度的化学风化。Co-Th-La-Sc 系统学揭示了页岩的镁铁质和长英质来源的组合。Eu/Eu* 以及 Th/U 值和一些微量元素的丰度表明页岩主要来自幼年岩。平均 REE 模型计算表明，源材料由大约 49% 的玄武岩、16% 的 TTG 和 35% 的花岗岩组成。Co-Th-La-Sc 系统学揭示了页岩的镁铁质和长英质来源的组合。Eu/Eu* 以及 Th/U 值和一些微量元素的丰度表明页岩主要来自幼年岩。平均 REE 模型计算表明，源材料由大约 49% 的玄武岩、16% 的 TTG 和 35% 的花岗岩组成。Co-Th-La-Sc 系统学揭示了页岩的镁铁质和长英质来源的组合。Eu/Eu* 以及 Th/U 值和一些微量元素的丰度表明页岩主要来自幼年岩。平均 REE 模型计算表明，源材料由大约 49% 的玄武岩、16% 的 TTG 和 35% 的花岗岩组成。