埃塞俄比亚默克莱大学Gebremicale, Azeb团队的一项最新研究，报道了埃塞俄比亚北部Tigrai Logomiti地区新元古代变质火山岩的地球化学特征，研究揭示了其岩石成因和构造环境的含义。相关论文发表在2024年6月26日出版的《地球化学学报》杂志上。

研究人员利用新的地质、岩石学、主要元素和微量元素资料对该区的变质作用、岩石成因和古构造背景进行了评价。野外和岩相观察表明，该区经历了绿片岩相变质作用。研究人员根据矿物学和地球化学特征，将这些变质火山岩分为玄武岩、玄武岩—安山岩、安山岩和英安岩。轻稀土元素(LREE)富集程度适中，重稀土元素(HREE)格局平坦，Nb/Y比值较低，代表浅地幔成因。

此外，TiO₂/Yb对Nb/Yb图，高(La/Yb)N比(>3.44)，表明岩浆存在浅熔和亏损岩浆。然而，(Th/Ta)>3.8， (La/Ta)>(Th/La)<1, (Nb/La) ＜1，Pb含量高表明岩浆受到地壳的混染。判别图和微量元素比值(Nb/Y、La/Sc、La/Y和La/Th)表明，变质火山岩具有钙碱性亲和性。此外，Zr-Nb-Y和Th-Hf-Ta图显示岩石形成于火山弧环境下。Tigrai Logomiti变质火山岩的岩石学和地球化学特征表明，该地区与阿拉伯Nubian地盾俯冲相关的岛弧增生有关。

附：英文原文

Title: Geochemistry of Neoproterozoic metavolcanic rocks from the Tahtai Logomiti area, Tigrai, Northern Ethiopia: Implication for petrogenesis and tectonic settings

Author: Gebremicale, Azeb, Alene, Mulugeta, Gidey, Teklay

Issue&Volume: 2024-06-26

Abstract: The Tahtai Logomiti area is characterized by metavolcanic and metavolcaniclastic interbedded with clastic and carbonate metasedimentary rocks of Neoproterozoic age. New geological, petrographic, major, and trace elements data were used to evaluate the metamorphism, petrogenesis, and paleo-tectonic setting of the area. The field and petrographic observation indicate that the area has undergone greenschist facies metamorphism. Based on mineralogy and geochemical attributes, these metavolcanic rocks are classified as basalt, basaltic-andesite, andesite, and dacite. The moderate degrees of light rare earth element (LREE) enrichment, flat heavy rare earth element (HREE) pattern, and low Nb/Y ratio, represent shallow mantle sources. In addition to that, the TiO₂/Yb vs. Nb/Yb diagram, high (La/Yb)N ratio (>3.44), indicates shallow melting and depleted magma sources. However, the high ratios of (Th/Ta)>3.8, (La/Ta)>38, and low ratios of (Th/La)<1, (Nb/La)<1, and high Pb content would indicate crustal contamination of the magma. The discrimination diagram and trace element ratios (Nb/Y, La/Sc, La/Y, and La/Th) indicate that the metavolcanic rocks have a calc-alkaline affinity. In addition, the Zr-Nb-Y and Th-Hf-Ta plots show that the rocks formed under a volcanic-arc setting. The general petrological and geochemical characteristics of the Tahtai Logomiti metavolcanic rocks suggest that the area is associated with subduction-related arc accretion of the Arabian Nubian Shield.

DOI: 10.1007/s11631-024-00712-3

Source: https://link.springer.com/article/10.1007/s11631-024-00712-3