安哥拉地盾Quibala地区古元古代斑状花岗岩的年代学、地球化学特征及地质意义
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1.山东省第一地质矿产勘查院;2.中信建设有限责任公司

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Geochronology, geochemistry and geological significance of Paleoproterozoic porphyritic granites in Quibala area, Angola Shield
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1.No.1 Institute of Geology and Mineral Resources of Shandong Province;2.Citic Construction Co., Ltd;3.No.1 Institute of Geology and Mineral Resource Exploration of Shandong Province

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    摘要:

    安哥拉前寒武纪经历多次构造旋回,其中以古元古代Eburnean旋回最为重要,对认识其构造演化过程具有重要地质意义。精确的年代学和地球化学数据的缺失,使得中央Eburnean区岩浆岩的形成时代尚缺乏有效数据支撑,也是造成岩石成因和构造演化尚未明确的主要原因之一。本文以发育在安哥拉地盾中央Eburnean区的Quibala斑状花岗岩为研究对象,开展了岩石学、年代学和地球化学研究。LA-ICP-MS锆石U-Pb年代学研究表明,Quibala斑状花岗岩的形成时代为1987~1956Ma,代表了Eburnean运动在安哥拉地盾的主体活动时间。岩石地球化学研究表明,斑状花岗岩具有富硅富碱高全铁,Ba、Sr、P、Ti元素亏损和Rb、Th、K、Hf元素富集,稀土元素总含量高的特征,说明其为A型花岗岩。此外,片麻岩等古老基底的捕虏体、含钾长石斑晶的闪长质包体及Rb/Nb、Th/U、Nb/Ta等特征元素比值说明其可能为壳幔物质混染的结果。Nb-Y-3Ga、Rb-(Y+Nb)等图解显示斑状花岗岩形成于古元古代的后碰撞伸展环境。

    Abstract:

    Angola has experienced several tectonic cycles in the Precambrian period, among which the paleoproterozoic Eburnean cycle is the most important one, which has important geological significance for understanding its tectonic evolution process. Due to the lack of accurate chronological and geochemical data, the formation age of magmatic rocks in the central Eburnean area is still not supported by effective data, which is also one of the main reasons for the unclear genesis and tectonic evolution of rocks. In this paper, the Quibala porphyritic granites in Eburnean area in the central Angolan Shield are studied in petrology, chronology and geochemistry. LA-ICP-MS zircon U-Pb chronology shows that the Quibala porphyritic granite was formed from 1987 to 1956Ma, which represents the main activity time of Eburnean movement in the Angora Shield. The geochemical study shows that porphyritic granite has high silicon, alkali, iron content, Ba, Sr, P, Ti elements deficit and Rb, Th, K, Hf elements enrichment, the total content of rare earth elements is high, indicating that it is A-type granite. In addition, the xenoliths of ancient basement such as gneiss, diorite inclusions containing potassium feldspar phenocrysts, and the ratios of Rb/Nb, Th/U, Nb/Ta and other characteristic elements indicate that the xenoliths may be the result of the mixing of crust-mantle materials. The NB-Y-3Ga and Rb- (Y+Nb) diagrams show that the granite porphyry was formed in the paleoproterozoic post-collision extensional environment.

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  • 收稿日期:2023-04-14
  • 最后修改日期:2023-05-27
  • 录用日期:2023-05-27
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