| 滇东南长安金矿晚始新世正长斑岩岩石地球化学、成岩时代及其地质意义 |
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| 引用本文：张垚垚,陈宣华,张达,莫宣学,邵兆刚,赵泽南,李兴俭.2022.滇东南长安金矿晚始新世正长斑岩岩石地球化学、成岩时代及其地质意义[J].地球学报,43(6):817-831. |
| DOI：10.3975/cagsb.2022.053102 |
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| 基金项目:中国地质调查局地质调查项目(编号: DD20190011; DD20201165);中国地质科学院基本科研业务费专项(编号: JKY202011) |
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| 中文摘要:滇东南长安金矿位于哀牢山造山带的南段, 矿区内主要出露的岩浆岩为正长斑岩, 常与金矿体伴生, 其形成时代及岩浆演化对长安金矿研究具有重要指示意义。本文选取正长斑岩样品进行岩石学、地球化学、锆石U-Pb和Hf同位素研究。研究表明, 正长斑岩SiO2含量为68.00%~70.43%, 全碱含量(K2O+Na2O)8.15%~8.76%, 属于亚碱性系列强过铝质岩石, 具S型花岗岩特征, ΣREE为71.52×10–6~76.43×10–6, 含量较低, 轻重稀土分异程度较大, 稀土配分曲线具右倾特征, 具δEu弱负异常(0.81~0.86)和δCe弱正异常(1.15~1.33), 微量元素蛛网图具右倾特征, Rb、Ba、Th、K等大离子亲石元素相对富集、高场强元素相对亏损, 具Nb、Ta负异常特征。岩体锆石发育震荡环带, Th/U比值较高, 锆石206Pb/238U分析点呈点群分布, 加权平均值为(34.7±0.3) Ma, 表明岩体形成于始新世晚期。锆石εHf(t)为–2.65~2.02, Hf单阶段模式年龄(TDM)为629.95~821.54 Ma, 二阶段模式年龄(TDMC)为1 378.52~1 801.25 Ma, 表明岩体主要由古老地壳成分部分重融形成, 混杂有少量幔源物质。岩石具埃达克岩特征, 形成于后碰撞构造背景。 |
| 中文关键词:正长斑岩 成岩时代 Lu-Hf同位素 长安金矿 |
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| Lithogeochemistry, Rock-forming Age, and Geological Implications of Late Eocene Syenite Porphyries in the Chang'an Gold Deposit, Southeastern Yunnan |
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| Abstract:The Chang'an gold deposit in southeastern Yunnan is located in the southern section of the Ailaoshan orogenic belt. The main exposed magmatic rocks in the mining area are syenite porphyries, which are often associated with gold ore bodies. The formation age and magmatic evolution of the syenite porphyries have important indicative significance for the study of the Chang'an gold deposit. In this study, syenite porphyry samples were selected for petrology, geochemistry, zircon U-Pb, and Hf isotope studies. Studies have shown that syenite porphyries have a SiO2 content of 68.00%–70.43% and a total alkali content (K2O+Na2O) of 8.15%–8.76%. It belongs to the sub-alkaline series of strong peraluminous rocks with the characteristics of S-type granites. The ΣREE is in the range of 71.52×10–6–76.43×10–6, with a low content and large degree of differentiation between light and heavy rare earth elements. The rare earth elements distribution curve has right-leaning characteristics, with δEu (0.81–0.86) weak negative anomalies and δCe (1.15–1.33) weak positive anomalies. The spider plot of trace elements is right-leaning, with enrichment of large ion lithophile elements such as Rb, Ba, Th, K, and depletion of highfield-strength elements, along with negative anomalies of Nb and Ta. The zircons of the pluton developed oscillating belts with a high Th/U ratio. The zircon 206Pb/238U analysis points are distributed in point groups with a weighted average of (34.7±0.3) Ma, indicating that the pluton was formed in the late Eocene. The zircon εHf(t) ranges from –2.65 to 2.02, single-stage Hf model ages (TDM) range from 629.95 Ma to 821.54 Ma, and two-stage Hf model ages (TDMC) range from 1 378.52 Ma to 1 801.25 Ma, suggesting that the plutons were formed as a result of remelting of ancient crustal components with a small number of mantle-derived materials. The rocks have adakite characteristics and were formed in a post-collisional tectonic setting. |
| keywords:syenite porphyries rock-forming age Lu-Hf isotope Chang'an gold deposit |
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