Onwualu-John J N
Department of Geology, University of Port Harcourt, Port Harcourt, Nigeria.
Environ Geochem Health. 2016 Aug;38(4):1029-35. doi: 10.1007/s10653-016-9817-1. Epub 2016 Mar 22.
Gabbroic rocks have intruded the sedimentary sequence at Ameta in Afikpo basin southeastern Nigeria. Petrographic and geochemical features of the rocks were studied in order to evaluate their genetic and geotectonic history. The petrographic results show that the rocks contain plagioclase, olivine, pyroxene, biotite, iron oxide, and traces of quartz in three samples. Major element characteristics show that the rocks are subalkaline. In addition, the rocks have geochemical characteristics similar to basaltic andesites. The trace elements results show inconsistent concentrations of high field strength elements (Zr, Nb, Th, Ta), moderate enrichment of large-ion lithophile elements (Rb, Sr, Ba) and low concentrations of Ni and Cr. Rare earth element results show that the rocks are characterized by enrichment of light rare earth elements, middle rare earth elements enrichment, and depletion of heavy rare earth elements with slight positive europium anomalies. Zinc concentrations are within the normal range in basaltic rocks. There are extremely high concentrations of Pb in three of the rock samples. The high Pb concentrations in some of these rocks could be as a result of last episodes of magmatic crystallization. The rocks intruded the Asu River Group; organic components in the sedimentary sequence probably contain Pb which has been assimilated into the magma at the evolutionary stage of the magma. Weathering of some rocks that contain galena could lead to an increase in the concentration of lead in the gabbroic rocks, especially when the migration and crystallization of magma take place in an aqueous environment. Nevertheless, high concentration of lead is hazardous to health and environment.
辉长岩侵入了尼日利亚东南部阿菲克波盆地阿梅塔的沉积层序。对这些岩石的岩相学和地球化学特征进行了研究，以评估它们的成因和大地构造历史。岩相学结果表明，这些岩石在三个样本中含有斜长石、橄榄石、辉石、黑云母、氧化铁和微量石英。主要元素特征表明这些岩石为亚碱性。此外，这些岩石具有与玄武安山岩相似的地球化学特征。微量元素结果显示，高场强元素（锆、铌、钍、钽）的浓度不一致，大离子亲石元素（铷、锶、钡）中等富集，镍和铬浓度较低。稀土元素结果表明，这些岩石的特征是轻稀土元素富集、中稀土元素富集、重稀土元素亏损且铕有轻微正异常。玄武岩中的锌浓度在正常范围内。在三个岩石样本中铅的浓度极高。这些岩石中部分铅浓度高可能是岩浆最后阶段结晶的结果。沉积层序中的有机成分可能含有铅，在岩浆演化阶段被岩浆同化。一些含方铅矿岩石的风化可能导致辉长岩中铅浓度增加，尤其是当岩浆在水环境中迁移和结晶时。然而，高浓度的铅对健康和环境有害。
