Late Cryogenian and Early Ediacaran rare metal-rich granites in the Eastern Desert of Egypt: constraints from zircon ages and whole-rock Sr- and Nd- and feldspar Pb- isotopic compositions

IF 2.6 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Journal of the Geological Society Pub Date : 2023-12-12 DOI:10.1144/jgs2023-068

R. Stern, M. Khedr, M. Whitehouse, Rolf L. Romer, Saif M. Abo Khashaba, N. H. El-Shibiny

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Abstract

Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to be found. In order to understand Neoproterozoic rare metal granites of the Arabian-Nubian Shield (ANS), six samples from five rare metal mineralized alkali feldspar granites, syenogranites and granodiorite from the Central and SE Desert of Egypt were studied for zircon U-Pb ages and O isotopic compositions as well as whole-rock Sr- and Nd- and alkali feldspar Pb- isotopic compositions. These are transitional between I-type and A-type granites, mostly high-K calc-alkaline, peraluminous granites with gullwing-shaped REE patterns and strongly negative Eu anomalies . Four granites gave mantle-like zircon δ 18 O V-SMOW between 4.2 and 5.96 ‰ and yielded ages of 628-633 Ma. This is about when subduction-related magmatism began to be replaced by collision-related magmatism. Igla Ahmr granites are older, formed at 691.7 - 678.9 Ma with δ 18 O V-SMOW ∼5.95 ‰ . All have positive initial ε Nd values (+3.3 to +6.9) typical for mantle and juvenile crust. Pb isotopic compositions are unusually radiogenic compared to unmineralized ANS granitic rocks. The data indicate similar magmatic sources for ANS mineralized and un-mineralized granites. Exploration for other rare-metal mineralized granites in the ANS should focus on bodies with similar characteristics. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6949402

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埃及东部沙漠晚冰期和早埃迪卡拉期富含稀有金属的花岗岩：锆石年龄和全岩Sr-、Nd-及长石Pb-同位素组成的制约因素

稀有金属（Nb、Ta、Y、Zr、Sn、U、W 和 REE）具有重要的经济价值，需要找到新的供应来源。为了了解阿拉伯-努比亚地盾（ANS）新元古代稀有金属花岗岩的情况，对埃及中部和东南部沙漠的五个稀有金属成矿碱长岩花岗岩、正长岩和花岗闪长岩的六个样本进行了研究，以了解锆石U-Pb年龄和O同位素组成，以及全岩Sr-、Nd-和碱长岩Pb-同位素组成。这些花岗岩介于 I 型和 A 型之间，大多为高 K 钙碱性过铝花岗岩，具有鸥翼形 REE 模式和强烈的负 Eu 异常。四块花岗岩的锆石δ 18 O V-SMOW介于4.2和5.96 ‰之间，年龄为628-633 Ma。这大约是与俯冲有关的岩浆活动开始被与碰撞有关的岩浆活动所取代的时间。Igla Ahmr 花岗岩的形成年代更早，为 691.7 - 678.9 Ma，δ 18 O V-SMOW ∼ 5.95 ‰。所有地幔和幼壳的初始ε钕值均为正值（+3.3 至 +6.9）。与未矿化的ANS花岗岩相比，Pb同位素组成具有异常的放射性。这些数据表明，ANS成矿花岗岩和未成矿花岗岩的岩浆来源相似。对ANS地区其他稀有金属矿化花岗岩的勘探应集中在具有类似特征的岩体上。补充材料：https://doi.org/10.6084/m9.figshare.c.6949402

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来源期刊

Journal of the Geological Society 地学-地球科学综合

CiteScore

6.00

自引率

3.70%

发文量

审稿时长

6-12 weeks

期刊介绍： Journal of the Geological Society (JGS) is owned and published by the Geological Society of London. JGS publishes topical, high-quality recent research across the full range of Earth Sciences. Papers are interdisciplinary in nature and emphasize the development of an understanding of fundamental geological processes. Broad interest articles that refer to regional studies, but which extend beyond their geographical context are also welcomed. Each year JGS presents the ‘JGS Early Career Award'' for papers published in the journal, which rewards the writing of well-written, exciting papers from early career geologists. The journal publishes research and invited review articles, discussion papers and thematic sets.