| 龙首山中段芨岭花岗岩体Sr-Nd-Pb同位素特征及意义 |
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| 引用本文： | 赵亚云,张树明,汤琳,尧宏福,杨春四.龙首山中段芨岭花岗岩体Sr-Nd-Pb同位素特征及意义[J].地球科学,2016,41(6):1016-1030. |
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| 作者姓名： | 赵亚云 张树明 汤琳 尧宏福 杨春四 |
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| 作者单位： | 1.东华理工大学省部共建核资源与环境国家重点实验室培育基地，江西南昌 330013 |
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| 基金项目： | 国家自然科学基金项目41172079 |
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| 摘 要： | 龙首山中段芨岭早古生代花岗岩体与碱交代型铀矿化关系密切，是龙首山花岗质岩浆活动带重要组成部分，但人们对芨岭岩体的成因、岩浆源区性质以及与铀成矿之间的关系还了解得不多.花岗岩体Sr-Nd-Pb同位素研究结果表明，不同期次花岗岩(早古生代第一次灰白色二长花岗岩、第二次肉红色二长花岗岩、晚古生代肉红色细粒(钾长)花岗岩)的(87Sr/86Sr)i值均介于大陆地壳范围内(0.706~0.718)，同时有(87Sr/86Sr)i均值先升后降(0.707 12→0.710 00→0.707 89)、εNd(t)均值先降后增(-7.00→-8.09→-4.65) 的特征.不同期次花岗岩体tDM2均值分别为1 735.50 Ma、1 814.66 Ma、1 737.50 Ma，接近残留地壳年龄，表明岩体的主要物质来源为古元古代龙首山群地层，并有部分幔源组分或年轻地壳物质的加入.岩体的Pb同位素比值较高，灰白色二长花岗岩的206Pb/204Pb=18.328~19.240，207Pb/204Pb=15.549~15.619，208Pb/204Pb=38.390~39.075，μ=9.37~9.43(平均为9.40)；肉红色二长花岗岩的206Pb/204Pb=30.209~43.529，207Pb/204Pb=16.097~25.076，208Pb/204Pb=39.107~39.420，μ=18.47~30.24(平均为24.355)；肉红色细粒(钾长)花岗岩的206Pb/204Pb=19.071~19.767，207Pb/204Pb=15.577~25.438，208Pb/204Pb=38.682~42.593，μ=9.36~9.49(平均为9.41)，显示为高放射性成因铅同位素特征，表明岩体的铅为混合来源但以壳源为主.Sr-Nd-Pb同位素对比研究表明，钠交代岩(矿石)的(87Sr/86Sr)i、εNd(t)与早古生代第二次侵入的肉红色斑状二长花岗岩极为相似，在(87Sr/86Sr)i-εNd(t)图解投影点也吻合，表明研究区碱交代型铀成矿主要与早古生代第二次侵入有关.其他期次花岗岩体同样具有高铀背景值，表明其可能也提供了一定的铀源.
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| 关 键 词： | 早古生代 芨岭岩体 Sr-Nd-Pb同位素 岩浆源区 铀成矿 龙首山 地球化学 |
| 收稿时间： | 2015-12-25 |
Sr-Nd-Pb Isotopic Characteristics and Its Geological Significance of the Jiling Grantic Pluton in the Middle Longshou Mountains |
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| Abstract: | The Early Paleozoic granitic pluton has a closely genetic relationship with the Alkali metasomatism type uranium mineralization in the middle Longshou Moutains area, which is an important activity zone of Longshoushan granitic magma. However, people do not know more about the cause of Jiling rock mass, properties of magma source area and the relationship between Jiling rock mass and uranium mineralization. The Sr-Nd-Pb isotopic composition characteristics of granitic pluton show that the initial Sr isotope ratios (87Sr/86Sr)i of granite in different periods (with first intrusion of gray monzonitic granites in the Early Paleozoic, the pink monzonitic granites of the second intrusion, and pink fine-grained (potassium) granites of the intrusion in Late Paleozoic) fall in the range of that of the continental crust (from 0.706 to 0.718); at the same time, the average initial Sr isotope ratios (87Sr/86Sr)i has a trend of falling after rising (0.707 12→0.710 00→0.707 89), and the average of εNd(t) shows the trend of rising after falling (-7.00→-8.09→-4.65). tDM2 average of granites in different periods is 1 735.50 Ma, 1 814.66 Ma and 1 737.50 Ma respectively, which is very close to the age of residual crust, indicating that the main material source of the granitic pluton should be the group strata of paleoproterozoic Longshou mountains, with the addition of mantle or young crustal materials. Its Pb Isotope ratios are high: 206Pb/204Pb range from 18.328 to 19.240, 207Pb/204Pb range from 15.549 to 15.619, 208Pb/204Pb range from 38.390 to 39.075, μ values range from 9.37 to 9.43, with an average of 9.40, 206Pb/204Pb range from 30.209 to 43.529, 207Pb/204Pb range from 16.097 to 25.076, 208Pb/204Pb range from 39.107 to 39.42, μ values range from 18.47 to 30.24, with an average of 9.40;206Pb/204Pb range from 19.071 to 19.767, 207Pb/204Pb range from 15.577 to 25.438, 208Pb/204Pb range from 38.682 to 42.593, μ values range from 9.36 to 9.49, with an average of 9.41. All samples show high radioactive Pb isotopic characteristics with a mixed source, but the crust is the main source. The comparison of Sr-Nd-Pb Isotope shows that the initial Sr isotope ratios (87Sr/86Sr)i and εNd(t) of sodium metasomatic rock (ore) are very similar to those of pink monzonitic granites of the second intrusion in the Early Paleozoic, and the subpoint of (87Sr/86Sr)i-εNd(t) diagram is also consistent, which indicates that alkali metasomatism type uranium mineralization of the study area is mainly related to the second invasion in Early Paleozoic. The high uranium background values of granitic pluton in other periods show that it may also provide a source of uranium. |
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