Geochemistry of Metavolcanic Rocks from Northern Ethiopia: Insights for Neoproterozoic Tectonic Setting of Arabian–Nubian Shield

IF 1.1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
Misgan Molla, Mulugeta Alene, Takashi Sano, Daniel Meshesha, Hayelom Mengesha, Gebremariam Mesele
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Abstract

Major and trace element data were presented for the Mai Kenetal–Werii metavolcanic rocks within the Arabian–Nubian Shield to examine the petrogenesis and the tectonic setting of the area. Based on field observations and geochemical data, the metavolcanic rocks were classified into basalts, andesites, and dacite-rhyolites. The rocks are dominantly subalkaline (tholeiite to calc-alkaline) in composition. The low contents of Ni (0.1–78 ppm), Co (2–53 ppm), Cr (10–351 ppm), TiO2 (0.18–1.59 wt %), MgO (0.62–9.16 wt %) and relatively with high contents of Al2O3 (10.39–18.51 wt %) indicate that the rocks were formed from more evolved magmas. The chondrite-normalized REE patterns also showed moderate fractionation, with (La/Yb)N values ranging from 2.28 to 9.22, slightly negative to positive Eu anomalies (Eu/Eu*, 0.50–1.16), and relatively flat heavy REEs ((Gd/Yb)N = 0.12–1.79). The rocks display slight enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) relative to high field strength elements (HFSEs), representing rocks that were derived from more evolved magmas in a mature island arc setting. Whereas, the low ratios of Nb/La (0.17–1.66) and Nb/Yb (0.61–2.23), combined with low total REE content (ΣREE = 49.58–151.3 ppm), low Nb content (0.6–6.5 ppm), and high Zr/Nb ratios (20.7–96.67) indicate depleted mantle source. In addition, trace element ratios (Y/Nb = 4.11–15.44, Nb/Y = 0.06–0.24, La/Sc = 0.1–2.67, La/Y = 0.32–1.51 and La/Nb = 2.68–6.23) and discrimination diagrams (Zr/4–2Nb–Y, Th–Hf/3–Ta, and Th–Zr/117–Nb/16), indicate that the metavolcanic rocks have a calc-alkaline affinity that was formed in an island arc tectonic setting from subduction-related magmas within Arabian-Nubian Shield.

Abstract Image

埃塞俄比亚北部变质火山岩地球化学:对阿拉伯-努比亚盾新元古代构造背景的认识
本文对阿拉伯-努比亚地盾内的Mai Kenetal-Werii变质火山岩进行了主量元素和微量元素数据分析,探讨了该地区的岩石成因和构造背景。根据野外观测和地球化学资料,将变质火山岩划分为玄武岩、安山岩和英安岩流纹岩。岩石成分主要为亚碱性(拉斑岩-钙碱性)。Ni (0.1 ~ 78 ppm)、Co (2 ~ 53 ppm)、Cr (10 ~ 351 ppm)、TiO2 (0.18 ~ 1.59 wt %)、MgO (0.62 ~ 9.16 wt %)含量较低,Al2O3 (10.39 ~ 18.51 wt %)含量相对较高,表明岩石形成于较演化的岩浆。球粒陨石归一化稀土模式也表现出中等分异,(La/Yb)N值在2.28 ~ 9.22之间,Eu/Eu*值为0.50 ~ 1.16,Eu/Eu*值为负~正,重稀土元素(Gd/Yb)N = 0.12 ~ 1.79)相对平坦。轻稀土元素(lree)和大离子亲石元素(LILEs)相对于高场强元素(hfse)有轻微的富集,表明岩石来源于成熟岛弧环境中较演化的岩浆。低Nb/La(0.17 ~ 1.66)、低Nb/Yb(0.61 ~ 2.23)、低REE含量(ΣREE = 49.58 ~ 151.3 ppm)、低Nb含量(0.6 ~ 6.5 ppm)、高Zr/Nb含量(20.7 ~ 96.67)表明地幔源枯竭。微量元素比值(Y/Nb = 4.11 ~ 15.44, Nb/Y = 0.06 ~ 0.24, La/Sc = 0.1 ~ 2.67, La/Y = 0.32 ~ 1.51, La/Nb = 2.68 ~ 6.23)和鉴别图(Zr/4 ~ 2nb - Y, Th-Hf / 3-Ta, Th-Zr /117 ~ Nb/16)表明,该变质火山岩具有钙碱性亲和力,形成于岛弧构造背景下,由阿拉伯-努比盾内俯冲相关岩浆形成。
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来源期刊
Petrology
Petrology 地学-地球科学综合
CiteScore
2.40
自引率
20.00%
发文量
27
审稿时长
>12 weeks
期刊介绍: Petrology is a journal of magmatic, metamorphic, and experimental petrology, mineralogy, and geochemistry. The journal offers comprehensive information on all multidisciplinary aspects of theoretical, experimental, and applied petrology. By giving special consideration to studies on the petrography of different regions of the former Soviet Union, Petrology provides readers with a unique opportunity to refine their understanding of the geology of the vast territory of the Eurasian continent. The journal welcomes manuscripts from all countries in the English or Russian language.
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