The Neoproterozoic charnockite–granite association of Okpella intrudes metasedimentary and migmatite-gneiss complex rocks in the eastern Igarra Schist Belt, southwestern Nigeria. In order to unravel the complex processes involved in the formation and tectonic evolution of the Igarra Schist Belt during the Neoproterozoic, detailed field, petrographic and whole-rock geochemical study of the charnockite–granite association and metasedimentary rocks around Okpella was conducted. Published data on the metasedimentary rocks and Pan-African granitoids in different sectors of the belt were also compiled for detailed interpretations. The charnockites and granites of Okpella show primary magmatic mineralogy and geochemical characteristics. They are silicic (> 63 wt% SiO₂), metaluminous to peraluminous, high-K calc-alkaline, ferroan, post-collisional granitoids. The garnet-biotite schist, calc-silicate gneiss and quartzite in the area are low–medium grade metasedimentary rocks. The mineralogy and geochemistry of the charnockites suggest that the charnockitic melt was derived from mafic lower continental crust through partial melting and assimilation-fractionation processes. The granites probably originated from mixed melts derived from lower- to mid-crustal tonalites-trondhjemites-granodiorites and/or subducted metagreywackes and mantle-derived magmas (probably the charnockitic melt and/or its progenitor). The granites and charnockites are coeval and were presumably emplaced during the post-collisional stages of the Pan-African Orogeny. The garnet-biotite schist, calc-silicate gneiss and quartzite represent metamorphosed immature to slightly mature sedimentary rocks, probably greywacke, marl and subarkose, respectively, that were sourced from intermediate–acid rocks which underwent low–moderate chemical weathering with minor contribution from recycled sediment sources and deposited in active continental environments. The Neoproterozoic evolution of the Igarra Schist Belt, therefore, involved deposition and infolding of sediments in active continental margin during the early Pan-African followed by upwelling of basaltic magma from the mantle which underplated and crystallized in the lower continental crust and was subsequently partially melted to generate the charnockitic and granitic melts through mantle-crust interaction during the late Pan-African.

中文翻译：

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尼日利亚西南部奥克佩拉附近的新元古代砂岩-花岗岩结合体和准沉积岩的岩石学和地球化学

Okpella的新元古代砂岩-花岗岩结合体侵入了尼日利亚西南部Igarra Schist带东部的准沉积和辉长岩-片麻岩复杂岩石。为了弄清新元古代的伊加拉史密斯带形成和构造演化的复杂过程，对俄克拉佩拉附近的炭黑岩-花岗岩结合体和准沉积岩进行了详细的现场，岩石学和全岩石地球化学研究。还对已发布的有关该带不同区域的沉积岩和泛非花岗岩的数据进行了汇编，以进行详细解释。奥克佩拉的炭黑岩和花岗岩显示出主要的岩浆矿物学和地球化学特征。它们是硅质的（> 63 wt％SiO ₂），金属至高铝，高K钙碱性盐，亚铁和碰撞后的类花岗岩。该地区的石榴石-黑云母片岩，钙硅酸盐片麻岩和石英岩是中低品位的沉积岩。菱锰矿的矿物学和地球化学表明，菱镁矿熔体是通过部分熔融和同化-分馏过程从镁铁质下部大陆壳中提取的。花岗岩可能起源于下地壳至中地的同色岩-特德赫米特斯-闪闪闪长岩和/或俯冲的变质灰泥岩和地幔衍生的岩浆（可能是菱形熔岩和/或其祖先）的混合熔体。花岗岩和霞石是同时代的，大概是在泛非造山运动的碰撞后阶段被安置的。石榴石-黑云母片岩，钙硅酸盐片麻岩和石英岩分别代表未成熟到稍成熟的沉积岩，可能分别是格雷瓦克，泥灰岩和次黑糖，它们来自中酸性岩石，这些岩石经历了中度化学风化作用，回收的沉积物来源贡献很小，并沉积在活性炭中。大陆环境。因此，Igarra Schist带的新元古代演化涉及到泛非早期活跃大陆边缘的沉积物沉积和褶皱，接着是来自地幔的玄武岩浆涌升，并在下部大陆壳中进行了下沉和结晶，随后被部分融化。在泛非晚期通过地幔-地壳相互作用生成炭化岩和花岗岩熔岩。可能分别是格雷沃克岩，泥灰岩和次黑糖，它们来自中酸性岩石，这些岩石经历了中度化学风化作用，回收的沉积物来源贡献很小，并沉积在活跃的大陆环境中。因此，Igarra Schist带的新元古代演化涉及到泛非早期活跃大陆边缘的沉积物沉积和褶皱，随后地幔中玄武岩浆上升，并在下部大陆壳中发生了沉积和结晶作用，随后被部分融化了。在泛非晚期通过地幔-地壳相互作用生成炭化岩和花岗岩熔岩。可能分别是格雷沃克岩，泥灰岩和次黑糖，它们来自中酸性岩石，这些岩石经历了中度化学风化作用，回收的沉积物来源贡献很小，并沉积在活跃的大陆环境中。因此，Igarra Schist带的新元古代演化涉及到泛非早期活跃大陆边缘的沉积物沉积和褶皱，接着是来自地幔的玄武岩浆涌升，并在下部大陆壳中进行了下沉和结晶，随后被部分融化。在泛非晚期通过地幔-地壳相互作用生成炭化岩和花岗岩熔岩。它们来自中酸性岩石，这些岩石经历了中度化学风化作用，回收的沉积物来源贡献很小，并沉积在活跃的大陆环境中。因此，Igarra Schist带的新元古代演化涉及到泛非早期活跃大陆边缘的沉积物沉积和褶皱，接着是来自地幔的玄武岩浆涌升，并在下部大陆壳中进行了下沉和结晶，随后被部分融化。在泛非晚期通过地幔-地壳相互作用生成炭化岩和花岗岩熔岩。它们来自中酸性岩石，这些岩石经历了中度化学风化作用，回收的沉积物来源贡献很小，并沉积在活跃的大陆环境中。因此，Igarra Schist带的新元古代演化涉及到泛非早期活跃大陆边缘的沉积物沉积和褶皱，接着是来自地幔的玄武岩浆涌升，并在下部大陆壳中进行了下沉和结晶，随后被部分融化。在泛非晚期通过地幔-地壳相互作用生成炭化岩和花岗岩熔岩。