An Nd‐isotopic study was carried out on Palaeoproterozoic Birimian shales from the Wa‐Lawra volcanic belt, located in the southeastern margin of the West African Craton. The objective of this study was to assess the nature and average crustal residence ages of the source areas, and deduce the provenance of these shales. Nd‐model ages range from 2.12 to 2.58 Ga, which are within the range of Nd‐model ages reported for the Birimian volcanic rocks, suggesting that the Birimian volcanic rocks are the main sources of detritus for the Birimian shales. The ε_Nd values of the Birimian shales, calculated at an age of 2.1 Ga, which represents the time of the deposition of the Birimian shales, ranges from −1.65 to +3.01. The range of observed ε_Nd values (i.e., −1.65 to +3.01) suggest that the Birimian shales were predominantly derived from the juvenile Palaeoproterozoic crust, with minor contribution of older crustal material. ε_Nd(T) versus Th/Sc, and ƒ^Sm/Nd versus ε_Nd(T) systematics indicate that the provenance can be explained by mixing between Palaeoproterozoic volcanic arc rocks and variable amounts of Archean continental crustal rocks. Provenance modelling shows that the Birimian shales received at least 80% detritus from a juvenile Birimian volcanic arc. The mean Archean component is 8%, suggesting that the continental crust of the Wa‐Lawra Belt is clearly dominated by material derived directly from the mantle.

中文翻译：

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加纳西北部Wa-Lawra带古元古代双栖页岩的钕同位素组成：物源限制

对位于西非克拉通东南缘的Wa-Lawra火山带的古元古代Birimian页岩进行了Nd同位素研究。这项研究的目的是评估源区的性质和平均地壳停留年龄，并推论这些页岩的物源。Nd模式年龄范围为2.12至2.58 Ga，处于报道的Birimian火山岩Nd模式年龄范围内，这表明Birimian火山岩是Birimian页岩碎屑的主要来源。的ε_的Nd的Birimian页岩的值，在2.1镓，其表示Birimian页岩的沉积时的年龄计算，范围从-1.65到3.01。观测到的ε的范围内_的Nd值（即-1.65至+3.01）表明Birimian页岩主要来源于幼年古元古代地壳，旧地壳物质的贡献较小。ε_钕（Ť）对的Th / Sc和ƒ ^{SM /钕}与ε_钕（Ť）系统学表明出处可通过火山古元弧岩石和不同量的太古代大陆地壳岩石之间的混合来解释。种源建模显示，Birimian页岩至少有80％来自幼年Birimian火山弧碎屑。太古代的平均分量为8％，这表明Wa-Lawra带的大陆壳显然是由直接来自地幔的物质主导的。