Geochemical characteristics of Precambrian Basement rocks from southeastern Nigeria: an approach to their petrogenesis and tectonic setting.

IF 1.3 4区 地球科学 Q2 GEOLOGY Geologica Acta Pub Date : 2020-12-07 DOI:10.1344/geologicaacta2020.18.19
C. U. Ibe
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Abstract

Trace and Rare-Earth element geochemical study of twenty samples of migmatitic banded gneisses, garnet biotite schists, dolerites, granites and rhyolites was carried out in a bid to determine their petrogenetic and tectonic significance in the evolution of the southeastern Basement complex of Nigeria. The data shows that partial melting (crustal anatexis) of migmatitic gneisses and schists played a significant role in the evolution of the granitic intrusions. This is supported by the high incompatible (Rb/Sr = 0.16 to 1.31 and Ba/Sr = 0.75 to 6.21) elements ratio in the granitic intrusions than that of the migmatitic gneisses and schists (Rb/Sr, 0.051 to 0.824; Ba/Sr, 0.7 to 5). High ratios of Ba/Sr and Rb/Sr and lesser values of Ba/Rb ratios in some granitic intrusions than in others suggests increasing fractionation during the anatexis. The role of partial melting is also evident in the smooth REE patterns shown by most of these rocks and the negative Eu anomaly as indicated by the values of Eu/Eu* (0.097 to 0.7). LREE enrichment is evident in the high values of Ce/Yb N (12.08-174.5), La/Yb N (15.2-228.4) and La/Sm N (2.6-7.2) in the granitic intrusions. Tectonic discrimination diagrams of the rocks indicate that the basement rocks were most probably formed in a post-collision orogenic setting while the dolerite and the rhyolite were formed in within-plate anorogenic setting.
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尼日利亚东南部前寒武纪基底岩石地球化学特征:成因与构造背景探讨
对尼日利亚东南部基底杂岩的混染带状片麻岩、石榴黑云母片岩、白云岩、花岗岩和流纹岩等20个样品进行了微量元素和稀土元素地球化学研究,以确定它们在尼日利亚东南部基底杂岩演化中的成因和构造意义。资料表明,混染片麻岩和片岩的部分熔融作用(地壳深熔作用)对花岗质侵入体的演化起了重要作用。这与花岗质侵入岩的不相容元素比(Rb/Sr = 0.16 ~ 1.31, Ba/Sr = 0.75 ~ 6.21)高于杂染岩片麻岩和片岩(Rb/Sr, 0.051 ~ 0.824;Ba/Sr, 0.7 ~ 5)。某些花岗岩岩体Ba/Sr和Rb/Sr比值较高,Ba/Rb比值较低,说明在深熔过程中分选作用增加。部分熔融的作用也体现在这些岩石的光滑REE模式和Eu/Eu*值(0.097 ~ 0.7)的负Eu异常中。花岗岩侵入体中Ce/Yb N(12.08 ~ 174.5)、La/Yb N(15.2 ~ 228.4)和La/Sm N(2.6 ~ 7.2)值较高,显示出明显的轻稀土富集。岩石的构造判别图表明,基底岩最可能形成于碰撞后造山环境,而白云岩和流纹岩则形成于板块内造山环境。
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来源期刊
Geologica Acta
Geologica Acta 地学-地质学
CiteScore
2.50
自引率
6.70%
发文量
13
审稿时长
>12 weeks
期刊介绍: - Relevant conceptual developments in any area of the Earth Sciences. - Studies presenting regional synthesis. - Thematic issues or monographic volumes presenting the results from one or more research groups. - Short papers reflecting interesting results or works in progress. - Contributions and results from Research Projects, Workshops, Symposiums, Congresses and any relevant scientific activity related to Earth Sciences. - Geologica Acta aims to stimulate rapid diffusion of results and efficient exchange of ideas between the widespread communities of Earth Science researchers (with special emphasis on Latinamerica, the Caribbean, Europe, the Mediterranean
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